Book of Abstracts Book of Abstracts - Universität Konstanz
Book of Abstracts Book of Abstracts - Universität Konstanz
Book of Abstracts Book of Abstracts - Universität Konstanz
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Symposium on<br />
Size Selected Clusters<br />
<strong>Book</strong> <strong>of</strong><br />
<strong>Abstracts</strong><br />
28 February - 3 March 2005 in Brand / Austria<br />
http://www.s3c.uni-konstanz.de/
The S 3 C –<br />
Symposium on Size Selected<br />
Clusters<br />
was generously supported by:<br />
• German Science Foundation<br />
• Varian
Table <strong>of</strong> Contents<br />
FULL LENGTH TALKS AND HOT TOPICS......................................................................... 1<br />
POSTERS.................................................................................................................................. 33<br />
CARBON 35<br />
CHEMISTRY 43<br />
DYNAMICS 63<br />
MAGNETISM 77<br />
MATERIALS 83<br />
METHODS 91<br />
METALS 101<br />
MOLECULAR CLUSTERS 113<br />
PHASE TRANSITIONS 121<br />
RARE GASES 127<br />
SEMICONDUCTORS 135<br />
SOLVATIONS 141<br />
SURFACE 147<br />
AUTHOR INDEX.................................................................................................................... 167<br />
� Poster Session A (Monday evening): Metals, Molecular Clusters, Phase<br />
Transitions, Rare Gases, Semiconductors, Solvations, Surface<br />
� Poster Session B (Wednesday evening): Carbon, Chemistry, Dynamics,<br />
Magnetism, Materials, Methods<br />
� The poster numbers are given at the top <strong>of</strong> the abstracts which can be found in<br />
the author index at the end <strong>of</strong> this book.
Full Length Talks<br />
and Hot Topics<br />
1
Metallic clusters and oxygen<br />
Catherine Bréchignac<br />
Laboratoire Aimé Cotton, CNRS, Bâtiment 505, Université Paris Sud, 91405 Orsay cedex, France<br />
The interaction between metallic substance and oxygen is one <strong>of</strong> the most important<br />
chemical and biological process in nature. This talk will discuss two aspects <strong>of</strong> oxygen<br />
interaction with matter at nanometer-scale.<br />
The first part <strong>of</strong> the talk deals with the interaction between metallic clusters and oxygen. Here<br />
cluster acts as finite reservoir <strong>of</strong> electrons and it is shown how the reactivity strongly depends<br />
on cluster size.<br />
In a second part the cluster acts as a vehicle to bring oxide molecule locally on supported<br />
islands. Using fractal islands as a test case for non-equilibrium morphologies, we show evidence<br />
<strong>of</strong> oxide driven elongated pearled shapes similar to those observed in pearling instability <strong>of</strong><br />
membrane tubes with anchored polymers. Such a similarity indicates that the relaxation <strong>of</strong><br />
fractals shares the same universality as the shape transition in neurons and membrane tubes.<br />
3
4<br />
The Disapperarance <strong>of</strong> Nobility: Reactivity Studies on free Gold and<br />
Silver Clusters<br />
Ludger Wöste<br />
Freie <strong>Universität</strong> Berlin, Institut für Experimentalphysik, Arnimallee 14, D-14195 Berlin, Germany<br />
Contrary to the bulk metal the clusters <strong>of</strong> noble metals are very reactive. The process <strong>of</strong><br />
gold sensitisation in silver photography is a prominent example. Most exciting in this regard is<br />
the non-scalable size regime below about 100 atoms per particle [1], where the physical<br />
properties <strong>of</strong> noble metal clusters show very pronounced size and charge effects. Their<br />
comprehension requires a clear identification <strong>of</strong> their geometries and electronic structures. We<br />
investigated chemical reactions <strong>of</strong> mass-selected gold and silver clusters in a temperature<br />
controlled rf-ion trap setup. Product ion concentrations as a function <strong>of</strong> storage time enable the<br />
determination <strong>of</strong> reaction kinetics and reaction mechanisms on free clusters. As an example, the<br />
CO combustion reaction on small gold clusters is studied. It is known that supported gold<br />
clusters with few atoms up to nm size exhibit relevant catalytic properties. Our ion trap<br />
measurements reveal catalytic activity already for negatively charged gold dimers. When the<br />
reaction kinetics are investigated as a function <strong>of</strong> temperature, intermediate products with CO<br />
and O2 co-adsorbed can be isolated [2]. In contrast, small atomic silver clusters have not been<br />
found relevant for catalytic oxidation processes so far. Our investigations show for the first time<br />
evidence for a strongly size dependent catalytic activity <strong>of</strong> Agn- (n=1-13) [3]. In order to<br />
elucidate the details <strong>of</strong> their reaction dynamics, femtosecond pump-probe experiments were<br />
performed on the educts, products and intermediates.<br />
References<br />
[1] U. Landman, Int. J. Mod. Phys. B 6, 3623 (1992).<br />
[2] L. D. Socaciu, J. Hagen, T. M. Bernhardt, L. Wöste, U. Heiz, H. Häkkinen, U. Landman:<br />
“Catalytic CO oxidation by free Au2-: Experiment and theory”, J. Am. Chem. Soc. 125, 10437<br />
(2003).<br />
[3] L. D. Socaciu, J. Hagen, J. Le Roux, D. Popolan, T. M. Bernhardt, L. Wöste,<br />
S. Vajda: “Strongly cluster size dependent reaction behavior <strong>of</strong> CO with O2 on free silver cluster<br />
anions”, J. Chem. Phys. 120, 2078 (2004).
Infrared Spectroscopy <strong>of</strong> Metal Ion Complexes: Models for Metal<br />
Ligand Interactions and Solvation<br />
Michael A. Duncan<br />
Department <strong>of</strong> Chemistry, University <strong>of</strong> Georgia, Athens, GA 30602<br />
maduncan@uga.edu<br />
http://www.arches.uga.edu/~maduncan<br />
Weakly bound complexes <strong>of</strong> the form M + -Lx (M=Fe, Ni, Co, etc.; L=CO2, C2H2, H2O,<br />
benzene, N2) are prepared in supersonic molecular beams by laser vaporization in a pulsednozzle<br />
cluster source. These species are mass analyzed and size-selected in a reflectron time-<strong>of</strong>flight<br />
mass spectrometer. Clusters are photodissociated at infrared wavelengths with a Nd:YAG<br />
pumped infrared optical parametric oscillator/amplifier (OPO/OPA) laser or with a tunable<br />
infrared free-electron laser. M + -(CO2)x complexes absorb near the free CO2 asymmetric stretch<br />
near 2349 cm -1 but with an interesting size dependent variation in the resonances. Small clusters<br />
have blue-shifted resonances, while larger complexes have additional bands due to surface CO2<br />
molecules not attached to the metal. M + (C2H2)n complexes absorb near the C-H stretches in<br />
acetylene, but resonances in metal complexes are red-shifted with repect to the isolated<br />
molecule. Ni + and Co + complexes with acetylene undergo intracluster cyclization reactions to<br />
form cyclobutadiene. Transition metal water complexes are studied in the O-H stretch region,<br />
and partial rotational structure can be measured. M + (benzene) and M + (benzene)2 ions (M=V, Ti,<br />
Al) represent half-sandwich and sandwich species, whose spectra are measured near the free<br />
benzene modes. These new IR spectra and their assignments will be discussed as well as other<br />
new IR spectra for similar complexes.<br />
5
6<br />
Diffuse Electron States<br />
Kit H. Bowen, Jr.<br />
Department <strong>of</strong> Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, USA<br />
The extra electron in valence (conventional) anions resides in an orbital which is firmly<br />
grounded on the nuclear framework <strong>of</strong> the system, i.e., the extra electron is localized. Likewise,<br />
when such anions are solvated and become anion-molecule complexes, the extra electron<br />
usually remains localized with the anion. During photodetachment <strong>of</strong> the excess electron from<br />
such a cluster anion, this sub-anion acts as the chromophore, and the photoelectron spectrum<br />
reflects the characteristics <strong>of</strong> that anion, albeit stabilized and spectrally shifted to higher electron<br />
binding energy.<br />
In other cluster anions, however, the excess electrons are more delocalized, even though<br />
they remain closely associated with their nuclear frameworks. There is, however, still another<br />
class <strong>of</strong> molecular and cluster anions in which the excess electrons are neither localized nor<br />
closely associated with their nuclear frameworks, and these are anions with highly diffuse,<br />
excess electron distributions. Examples include dipole bound anions, quadrupole bound anions,<br />
double Rydberg anions, and some sizes <strong>of</strong> water cluster anions. While these species share the<br />
characteristic <strong>of</strong> having spatially diffuse excess electrons, they are otherwise bound by different,<br />
albeit idealized interactions. The excess electron in dipole bound anions is chiefly bound by the<br />
dipolar field <strong>of</strong> the corresponding neutral system, with the excess electron ballooning out into<br />
space at the positive end <strong>of</strong> the molecular or cluster system. Similarly, the excess electron in<br />
quadrupole bound anions is primarily bound by the quadrupolar field <strong>of</strong> the corresponding<br />
neutral system. Double Rydberg anions are the negative ions <strong>of</strong> Rydberg radicals. Each one can<br />
be thought <strong>of</strong> as a closed shell, cationic core which is enveloped by two Rydberg-like, highly<br />
diffuse electrons. Also, many water cluster anion systems appear to exhibit diffuse excess<br />
electron states <strong>of</strong> at least two types, with a third type being associated with internalizing<br />
electron states.<br />
In this talk, we will survey these different types <strong>of</strong> diffuse electron states, but we will focus<br />
on double Rydberg anions, in part because they are the least well-known diffuse, excess electron<br />
species. In particular, we will discuss the ammonia-based double Rydberg anions, (NnH3n+1) - ,<br />
where n = 1- 7. Using anion photoelectron spectroscopy, we have measured electron affinities<br />
<strong>of</strong> these species, found examples <strong>of</strong> solvated double Rydberg anions, and accessed the first<br />
electronic states <strong>of</strong> several neutral Rydberg radicals by photodetaching electrons from their<br />
corresponding double Rydberg anions. Insight into the nature <strong>of</strong> these species was further aided<br />
by comparisons with the absorption measurements <strong>of</strong> Fuke on neutral Rydberg cluster-like<br />
radicals and by several theoretical studies, especially those <strong>of</strong> Ortiz.
Model Gold Catalysts by Size-Selected Cluster Deposition<br />
Sungsik Lee, Chaoyang Fan, Tianpin Wu, and Scott L. Anderson<br />
Dept. <strong>of</strong> Chemistry, University <strong>of</strong> Utah, 315 S. 1400 E. Rm 2020, Salt Lake City UT 84112, USA<br />
Planar model gold catalysts were prepared by deposition <strong>of</strong> size- and energy-selected gold<br />
cluster cations, on well characterized supports in UHV. The CO oxidation reaction was used to<br />
characterize the chemical behavior <strong>of</strong> the resulting samples. As shown in the figure, strongly<br />
size-dependent activity is observed for room temperature CO oxidation on Aun/TiO2, with<br />
significant activity observed for n ≥ 3. No activity is observed for Au/Al2O3. Detailed studies<br />
over a wide temperature range, using x-ray photoelectron spectroscopy (XPS), ion scattering<br />
spectroscopy (ISS), and CO thermal adsorption and desorption were used to probe the nature <strong>of</strong><br />
the samples resulting from cluster deposition. It is found that on titania, the gold migrates to<br />
surface oxygen vacancy sites between 200 and 300K, and appears to be stably trapped at the<br />
vacancies at room temperature. XPS shows that binding at the vacancies injects electron density<br />
into the clusters, and absence <strong>of</strong> this effect on alumina is probably responsible for the observed<br />
lack <strong>of</strong> activity. At T ≥ 450 K, significant agglomeration occurs. Correlations <strong>of</strong> activity with<br />
the cluster morphology and ability to bind CO and O2, both on the clusters, and in adjacent<br />
substrate sites, will be discussed.<br />
C 16 O 18 O+ intensity (arb.)<br />
7e+5<br />
6e+5<br />
5e+5<br />
4e+5<br />
3e+5<br />
2e+5<br />
1e+5<br />
0<br />
CO oxidation<br />
TiO2 Au1 Au2 Au3 Au4 Au5 Au6 Au7<br />
7
8<br />
Structural Order in Metal Clusters: Dependence on Size and Charge<br />
State<br />
Joel H Parks<br />
Rowland Institute at Harvard, Cambridge, Massachusetts 02142<br />
Trapped ion electron diffraction (TIED) has been applied to Ag and Au cluster ions<br />
produced by a sputter discharge aggregation source. A specific cluster size is selectively stored<br />
in an rf ion trap in which the trapped ions are annealed and brought into thermal equilibrium<br />
with a background He gas. The stored ions are then exposed to a high energy electron beam and<br />
electron scattering is imaged by a multichannel plate detector onto a phosphor screen.<br />
Diffraction patterns are collected by a CCD camera and analyzed to extract the molecular<br />
interference directly related to the arrangement <strong>of</strong> atoms in the mass selected cluster.<br />
Following a brief introduction to TIED experiment and analysis, this talk will present recent<br />
measurements for Agn + cations, and Aun -/+ cation and anion clusters. Two principal results will<br />
be discussed: the transition from local to global five-point order in Agn + clusters over the size<br />
range 36≤n≤55, and the dependence <strong>of</strong> Aun -/+ structures on charge state for n=20,32,38 and 55.<br />
Diffraction data will be compared with isomer structures predicted by density functional<br />
calculations and molecular dynamic simulations. Experimental opportunities for diffraction<br />
measurements will be briefly considered.
Ultra-stable Hetero-nuclear Microclusters <strong>of</strong> (CdSe)33 and (CdSe)34<br />
Atsuo Kasuya 1 , Rajaratnam Sivamohan 1 , Yurii A. Barnakov 1 , Igor M. Dmitruk 1,6 , Takashi Nirasawa 2,3 ,<br />
Grzegorz Milczarek 1 , Sergiy V. Mamykin 1 , Volodymyr R. Romanyuk 1 , Kazuyuki Tohji 2 , Valachandran<br />
Jeyadevan 2 , Kozo Shinoda 2 , Toshiji Kudo 3 , Osamu Terasaki 4 , Zheng Liu 4 , Tetsu Ohsuna 5 , Rodion V.<br />
Belosludov 5 , Vijay Kumar 1,5 , Vijayaraghavan Sundararajan 1 , Yoshiyuki Kawazoe 5<br />
1 Center for Interdisciplinary Research, Tohoku University, Sendai, 980-8578, Japan<br />
2 Department <strong>of</strong> Geoscience and Technology, Tohoku University, Sendai, 980-8579, Japan<br />
3 Bruker Daltonics K.K., Kanagawa-ku, Yokohama, 221-0022, Japan<br />
4 Department <strong>of</strong> Physics, Tohoku University, Sendai, 980-8578, Japan<br />
5 Institute for Material Research, Tohoku University, Sendai, 980-8577, Japan<br />
6 Kyiv National Taras Shevchenko University, Kyiv, 03022, Ukraine<br />
Time-<strong>of</strong>-Flight mass spectra reveal that nanoparticles, (CdSe)n, grown in solution can be mass<br />
selected at atomic level by reverse micelle method. This method allows us to produce<br />
macroscopic quantity <strong>of</strong> (CdSe)33 and (CdSe)34 by making use <strong>of</strong> their highly selective<br />
stabilities in reverse micelles [1]. This preferential growth at particular n’s depicted by mass<br />
spectra suggests that the structure <strong>of</strong> these particles is quite different from a bulk fragment and<br />
is high-symmetric (CdSe)28 cage incorporating 5 or 6 CdSe pairs inside and forming sp 3<br />
network. Similar selective stabilities have been found in CdS and other A II B VI compounds,<br />
demonstrating that such highly stabilied clusters may be found in a variety <strong>of</strong> compound<br />
systems.<br />
Figure 1. Time-<strong>of</strong>-flight mass spectra <strong>of</strong> positive ions from (CdSe) n prepared in toluene (curve 1), and from powders<br />
<strong>of</strong> bulk CdSe (curve 2) and CdS (curve 3). Suggested structure <strong>of</strong> (CdSe) 34 cluster.<br />
References<br />
[1] Kasuya A., Sivamohan R., Barnakov Yu., Dmitruk I., et al, Nature Materials 3, 99 (2004).<br />
9
Dynamics and spectroscopy <strong>of</strong> anion clusters and helium nanodroplets<br />
10<br />
Daniel M. Neumark<br />
Department <strong>of</strong> Chemistry, University <strong>of</strong> California, Berkeley, CA. USA 94720, and Chemical Sciences<br />
Division, Lawrence Berkeley National Laboratory, Berkeley, CA USA 94720<br />
Recent results on the spectroscopy and dynamics <strong>of</strong> water cluster anions and helium<br />
nanodroplets will be presented. Mass-selected (H2O)n - and (D2O)n - anions were studied using<br />
one-photon and time-resolved photoelectron imaging. The one-photon studies established the<br />
existence <strong>of</strong> both internal and surface states <strong>of</strong> water clusters anions, and showed that one can<br />
switch between isomers by varying ion source conditions. The time-resolved studies yielded<br />
excited state lifetimes for both isomers, showing dramatically different dependence on cluster<br />
size. Extrapolation <strong>of</strong> the internal conversion rates for the internal states to the bulk limit<br />
strongly supports the “non-adiabatic” relaxation mechanism proposed for the hydrated electron<br />
in aqueous solution.<br />
The photoionization and photoelectron spectroscopy <strong>of</strong> He nanodroplets was investigated using<br />
synchrotron radiation at the Advanced Light Source at Lawrence Berkeley National Laboratory.<br />
Photoelectron images were obtained at photon energies below and above the ionization potential<br />
<strong>of</strong> atomic He (24.6 eV). The images below the IP were dominated by extremely slow electrons,<br />
with an average energy <strong>of</strong> < 1 meV, believed to originate from excitation and autoionization <strong>of</strong><br />
a Hen subunit within the cluster followed by thermalization <strong>of</strong> the electron before it leaves the<br />
cluster. The images above the IP are very different, showing photoelectron signal at higher<br />
energy than that seen from atomic He. This high energy signal is attributed to direct detachment<br />
to the attractive region <strong>of</strong> Hen+ potential energy surfaces.
Tailoring functionality <strong>of</strong> clusters by size, structures and lasers<br />
Vlasta Bonačić-Koutecký<br />
Humboldt <strong>Universität</strong> zu Berlin, Institut für Chemie, Brook-Taylor-Strasse 2,<br />
D-12489 Berlin, Germany, e-mail: vbk@chemie.hu-berlin.de<br />
Theoretical exploration <strong>of</strong> cluster properties for which each atom counts will be presented<br />
for the following topics:<br />
1. Chemical reactivity <strong>of</strong> nobel-metal oxides as foundation for design <strong>of</strong> nanoscale<br />
catalytic materials.<br />
2. Emissive properties <strong>of</strong> silver particles at silver oxide defects as attractive candidates for<br />
optical data storage.<br />
3. Ultrafast dynamics and its control by tailored laser fields in clusters and in their<br />
complexes with biomolecules for selection <strong>of</strong> reaction channels and <strong>of</strong> photochemical<br />
processes.<br />
4. Importance <strong>of</strong> mutual interaction between theory and experiment for all three subjects<br />
will be illustrated.<br />
11
A new infrared spectroscopy technique for structural studies <strong>of</strong> massselected<br />
neutral polar molecular species without chromophore<br />
12<br />
B. Lucas, F. Lecomte, G. Grégoire, Y. Bouteiller, J.-P. Schermann, C. Desfrançois<br />
Lab. de Physique des Lasers, CNRS-Univ. Paris-Nord, 93430 Villetaneuse, France<br />
We will present a new infrared spectroscopy technique for structural studies <strong>of</strong> massselected<br />
neutral polar molecules or complexes without chromophore [1]. In these experiments,<br />
we use dipole-bound anion formation, as a totally non-perturbative ionization method. Anion<br />
signal depletion allows us to monitor IR absorption, in between 2700 and 3800 cm -1 , on massselected<br />
neutral species. For weakly bound complexes, with typical H-bond dissociation<br />
energies about 1500 cm -1 , IR absorption indeed leads to fast vibrational predissociation prior to<br />
ionization. For both isolated molecules and complexes, the very weak excess electron binding<br />
energy (typically 100 cm -1 ) in dipole-bound anions also allows for vibrational autodetachment<br />
due to IR absorption. In both cases, the signature <strong>of</strong> IR absorption by the neutral species is a<br />
loss in the dipole-bound anion signal at the corresponding mass. This is an alternative technique<br />
to the IR-REMPI technique when the neutral species do not possess any chromophore.<br />
We will discuss results on small molecules and clusters containing water and formamide:<br />
water dimer, formamide-water complex, isolated formamide and formamide dimer. These four<br />
test-cases exemplify the capabilities and limitations <strong>of</strong> this technique and allow us to plan for<br />
future technical improvements in order to gain sensitivity for further experiments on molecules<br />
and complexes <strong>of</strong> biological interest. Experimental IR spectra will be interpreted with the help<br />
<strong>of</strong> quantum chemistry calculations. In particular, the use <strong>of</strong> anharmonic frequency calculations<br />
will be discussed.<br />
relative anion signal depletion<br />
0.4<br />
0.2<br />
0.0<br />
-0.2<br />
-0.4<br />
-0.6<br />
-0.8<br />
-1.0<br />
free CH<br />
2850 2900 2950<br />
bonded<br />
NH / OH<br />
free NH<br />
?<br />
3400 3450 3500 3550<br />
frequency (cm -1 )<br />
free OH<br />
3700 3750<br />
IR spectrum <strong>of</strong> mass-selected neutral formamide-water complexes obtained from dipole-bound anion signal<br />
depletion. Small squares correspond to relative depletion values averaged over 3 independent measurements while<br />
full thick lines correspond to a smooth over 3 adjacent points. Experimental line positions are indicated by thin dash<br />
lines and theoretical frequencies are located by full (anharmonic values) or dash (scaled harmonic values) bars. The<br />
question mark corresponds to a line that is not assigned.<br />
References<br />
[1] B. Lucas, F. Lecomte, B. Reimann, H.-D. Barth, Gilles Grégoire, Y. Bouteiller, J.-P. Schermann,<br />
C. Desfrançois, Phys. Chem. Chem. Phys. 6, 2600 (2004).
The hydrogen transfer reaction: from molecular clusters to proteins<br />
C. Jouvet 1 , H. Kang 1 , C. Dedonder-Lardeux 1 , G. Grégoire 2 , C. Desfrançois 2 , J-P. Schermann 2 , M. Barat 3<br />
and J. A. Fayeton 3<br />
1 Laboratoire de Photophysique Moléculaire du CNRS et Laboratoire ELYSE, Bat349, Université Paris-<br />
Sud, 91405 Orsay, France.<br />
2 Laboratoire de Physique des Lasers du CNRS, Institut Galilée, Université Paris-Nord, 93430<br />
Villetaneuse, France.<br />
3 Laboratoire des Collisions Atomiques et Moléculaires du CNRS, Université Paris-Sud, 91405 Orsay,<br />
France.<br />
Four years ago we have demonstrated that the excited state reaction <strong>of</strong> phenol-amonnia<br />
clusters is an H atom transfer leading to the formation <strong>of</strong> hypervalent NH4(NH3)n clusters 1, 2 , and<br />
not by a proton transfer as suggested by the liquid phase experiments. This first observation lead<br />
to the developement <strong>of</strong> a more general model 3 where a surprisingly simple and general<br />
mechanistic picture for the nonradiative decay <strong>of</strong> aromatic biomolecules such as nucleic bases<br />
and aromatic amino acids has been suggested.<br />
The key role in this model is played by an excited singlet state <strong>of</strong> πσ* character, which has<br />
a repulsive potential-energy function with respect to the stretching <strong>of</strong> OH or NH bonds. The<br />
1 πσ∗ potential-energy function intersects not only the bound potential-energy functions <strong>of</strong> the<br />
1 ππ∗ excited states, but also that <strong>of</strong> the electronic ground state 3 . Via predissociation <strong>of</strong> the 1 ππ∗<br />
states and a conical intersection with the ground state, the � πσ* state triggers an internalconversion<br />
(IC) process. The lifetime <strong>of</strong> the optically excited � ππ∗ state is governed by the first<br />
intersection which determines the barrier for IC process, and varies from one molecule to the<br />
other depending largely on the energy gap between the 1 πσ∗ and the 1 ππ* states.<br />
In clusters <strong>of</strong> phenol or indole 4 and ammonia, calculations predict that the H transfer leads<br />
to the formation <strong>of</strong> hydrogenated ammonia clusters NH4(NH3)n through an avoided crossing<br />
between the 1 ππ∗ and the 1 πσ∗ states 5 . In this system the reaction seems to proceed via<br />
tunneling, since the process is fast in the hydrogenated species and considerably slower for<br />
deuterated species 6-7 . We recently demonstrated that this model also applies in protonated<br />
aromatic amino acid (tryptophan, tyrosine) and explains why the excited state lifetime <strong>of</strong><br />
protonated Tryptophan (400fs) 8 is ten times shorter than the lifetime <strong>of</strong> protonated Tyrosine.<br />
References<br />
[1] G. Pino, G. Gregoire, C. Dedonder-Lardeux, C. Jouvet, S. Martrenchard and D. Solgadi, Physical<br />
Chemistry Chemical Physics, 2000, 2, 893-900.<br />
[2] G. A. Pino, C. Dedonder-Lardeux, G. Gregoire, C. Jouvet, S. Martrenchard and D. Solgadi, J.<br />
Chem. Phys., 1999, 111, 10747.<br />
[3] A. L. Sobolewski, W. Domcke, C. Dedonder-Lardeux and C. Jouvet, Phys. Chem. Chem. Phys.,<br />
2002, 4, 1093-1100.<br />
[4] C. Dedonder-Lardeux, D. Grosswasser, C. Jouvet and S. Martrenchard, Physchemcomm, 2001,<br />
1-3.<br />
[5] A. L. Sobolewski and W. Domcke, J. Phys. Chem. A, 2001, 105, 9275.<br />
[6] G. Gregoire, C. Dedonder-Lardeux, C. Jouvet, S. Martrenchard, A. Peremans and D. Solgadi,<br />
Journal <strong>of</strong> Physical Chemistry A, 2000, 104, 9087-9090.<br />
[7] S. Ishiuchi, K. Daigoku, M. Saeki, K. Hashimoto, M. Sakai and M. Fujii, J. Chem. Phys., 2002,<br />
117, 7077.<br />
[8] H. Kang, C. Jouvet, C. Dedonder-Lardeux, S. Martrenchard, G. Grégoire, C. Desfrançois, J.-P.<br />
Schermann, M. Barat and J. A. Fayeton, P.C.C.P., 2004, to be published.<br />
13
14<br />
Immobilisation <strong>of</strong> proteins by size-selected nanoclusters on surfaces<br />
Richard E. Palmer<br />
Nanoscale Physics Research Laboratory, School <strong>of</strong> Physics and Astronomy, The University <strong>of</strong><br />
Birmingham, Birmingham B15 2TT, UK<br />
r.e.palmer@bham.ac.u<br />
www.nprl.bham.ac.uk<br />
The controlled deposition <strong>of</strong> size-selected nanoclusters represents a novel route to the<br />
fabrication <strong>of</strong> nanostructured surfaces, generating lateral features <strong>of</strong> size 1-10 nm. This is<br />
precisely the size scale <strong>of</strong> biological molecules and provides a new method to immobilize<br />
individual proteins, with potential applications in structural biology, protein complex formation<br />
and high throughput medical diagnostics (microarrays).<br />
Scaling relations which describe both the implantation [1] and pinning [2] <strong>of</strong> the clusters<br />
enable the controlled preparation <strong>of</strong> 3D, nanoscale surface features, stable to temperatures as<br />
high as 400°C. In particular, we report the pinning <strong>of</strong> size-selected AuN clusters (N = 1 – 100) to<br />
the hydrophobic graphite surface to create films <strong>of</strong> arbitrary, sub-monolayer density. Gold<br />
presents an attractive binding site for sulphur and thus potentially for the cysteine amino acid<br />
residues in proteins (which contain a thiol, SH, group), suggesting the possibility <strong>of</strong> residuespecific<br />
immobilization <strong>of</strong> oriented protein molecules.<br />
AFM measurements in liquid (buffer) solution show that GroEL chaperonin molecules<br />
(ring-shaped molecules with diameter 15 nm), which contain free cysteine residues, bind to the<br />
clusters and are immobilised [3]. Both peroxidase molecules [4], in which the cysteine residues<br />
pair up to form disulphide bonds, and oncostatin molecules can similarly be immobilised. In<br />
both cases protein clusters are also formed. By contrast, green fluorescent protein (GFP) and<br />
luciferase molecules do not bind to the nanoclusters. The behaviour <strong>of</strong> the different protein<br />
molecules is predicted by a model, based on molecular surface area calculations, which<br />
considers the “accessibility” <strong>of</strong> cysteine (and other) residues at the outer surface <strong>of</strong> the folded<br />
protein. The results demonstrate the ground rules for, and generality <strong>of</strong>, protein immobilisation<br />
by metal cluster films.<br />
Finally, I will discuss ongoing experiments with human IgG molecules which seem to<br />
present the first evidence that protein immobilization depends on cluster size.<br />
References<br />
[1] S. Pratontep, P. Preece, C. Xirouchaki, R.E. Palmer, C.F. Sanz-Navarro, S.D. Kenny and R. Smith,<br />
Phys. Rev. Lett. 90 055503 (2003).<br />
[2] S.J. Carroll, S. Pratontep, M. Streun, R.E. Palmer, S. Hobday and R. Smith, J. Chem. Phys. 113<br />
7723 (2000); also Nature (News & Views) 408 531 (2000).<br />
[3] R.E. Palmer, S. Pratontep and H.-G. Boyen, Nature Materials 2 443 (2003).<br />
[4] C. Leung, C. Xirouchaki, N. Berovic and R.E. Palmer, Adv. Mater. 16 223 (2004).
Atomic and Molecular Architecture at Surfaces<br />
Klaus Kern<br />
Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart<br />
klaus.kern@fkf.mpg.de<br />
A promising route toward the realization <strong>of</strong> functional nanosystems is the exploitation <strong>of</strong><br />
nature’s inherent drive to generate complexity. The transcription <strong>of</strong> the corresponding<br />
organization principles to artificial compounds and environments comprises intriguing<br />
perspectives. We emphasize the conductance <strong>of</strong> self-organized growth processes at well-defined<br />
surfaces. The atomistic insight gained into the underlying mechanisms and interactions is used<br />
to control the formation <strong>of</strong> low-dimensional atomic and molecular architectures. This knowhow<br />
opens up new avenues in engineering nanomaterials <strong>of</strong> well-defined shape, composition<br />
and functionality to be harnessed for future technological applications.<br />
15
Size-Selected Aun and Agn Clusters on Rutile TiO2 (110) (1x1) Surfaces<br />
Probed by UHV-STM<br />
16<br />
Steven K. Buratto, Xiao Tong, Lauren Benz, Andrei Kolmakov, Paul Kemper, Steeve Chrétien, Horia<br />
Metiu, and Michael T. Bowers<br />
Department <strong>of</strong> Chemistry and Biochemistry, University <strong>of</strong> California, Santa Barbara<br />
Santa Barbara, CA 93106-9510, United States <strong>of</strong> America<br />
Catalysis <strong>of</strong> the oxidation <strong>of</strong> CO and small olefins by nanoclusters <strong>of</strong> Au and Ag on oxide<br />
supports is known to be strongly dependent on the size <strong>of</strong> the cluster and its interaction with the<br />
oxide support. In our group we have probed the size dependence by depositing size-selected<br />
clusters <strong>of</strong> Agn + and Aun + (n = 1-7) from the gas phase onto single crystal rutile TiO2 (110) (1x1)<br />
surfaces at room temperature under s<strong>of</strong>t-landing (< 2 eV/atom) conditions. We analyze the<br />
clusters on the surface using ultra-high vacuum scanning tunneling microscopy (UHV-STM)<br />
and compare the resulting structures with theory. In the case <strong>of</strong> Ag + and Ag2 + clusters deposited<br />
under s<strong>of</strong>t-landing conditions (Figure 1), we observe large, sintered clusters indicating high<br />
mobility for these species on the surface. For Agn + (n ≥ 3) clusters (also shown in Fig. 1)<br />
deposited under s<strong>of</strong>t-landing conditions, however, we observe a high density <strong>of</strong> intact clusters<br />
bound to the surface and no large, sintered clusters indicating that these species have very<br />
limited mobility on the surface.<br />
Figure 1. STM Images <strong>of</strong> the titania surface after the deposition <strong>of</strong> Ag 1, Ag 2, and Ag 3, respectively, from left to right.<br />
All images are 100 nm x 100 nm, insets are ~ 7 nm x 7 nm.<br />
In the case <strong>of</strong> Aun + clusters, we observe large, sintered clusters only from the deposition <strong>of</strong> Au +<br />
and a high density <strong>of</strong> intact clusters from the deposition <strong>of</strong> Aun + (n ≥ 2) as depicted in Figure 2.<br />
In cases where we observe intact clusters we can observe the binding site and geometry in the<br />
STM image and compare these with structures calculated using density functional theory (DFT)<br />
as well as structures observed in the gas phase.<br />
Figure 2. STM Images <strong>of</strong> the titania surface after the deposition <strong>of</strong> Au 1, Au 2, Au 3, Au 4 and Au 7, respectively, from<br />
left to right. All images are 100 nm x 100 nm, insets are ~ 7 nm x 7 nm.
Magnetic Properties <strong>of</strong> Deposited Transition Metal Atoms and<br />
Clusters<br />
Matthias Reif, Leif Glaser, Michael Martins, Wilfried Wurth<br />
Insitut für Experimentalphysik, <strong>Universität</strong> Hamburg, Luruper Chaussee 149,<br />
Hamburg, D-22761, Germany<br />
From a fundamental point <strong>of</strong> view size-selected transition metal clusters allow to study the<br />
transition from the magnetic properties <strong>of</strong> atoms to those <strong>of</strong> the respective solids as a function <strong>of</strong><br />
cluster size. For possible future applications these clusters have to be supported on a substrate <strong>of</strong><br />
embedded in a matrix where cluster-support interaction will influence theier physical properties<br />
as well. We have therefore started to investigate the magnetic properties <strong>of</strong> small transition<br />
metal clusters in contact with ferromagnetic substrates as a function <strong>of</strong> the number n <strong>of</strong> cluster<br />
atoms in the size region from n=2 to n=20.<br />
To achive thos goal we have developed a UHV-compatible cluster source, which enables us to<br />
investigate size selected transition metal clusters deposited in-situ under UHV conditions on<br />
solid surfaces using s<strong>of</strong>t X-ray spectroscopy at third generation synchrotron radiation sources.<br />
This contribution will discuss especailly x-ray magnetic circular dichroism (XMCD) studies <strong>of</strong><br />
size selected deposited clusters and recent experimental results <strong>of</strong> supported 3d and 4d transition<br />
metal clusters will be presented. For iron clusters [1,2] on nickel a strong size dependence <strong>of</strong> the<br />
spin- and orbital moment, which could be measured independently with the XMCD method, are<br />
found. In particular the orbital moment per iron atom is strongly enhanced as compared to the<br />
values <strong>of</strong> bulk solid or ultrathin films.<br />
Recent experimental and theoretical studies on chromium clusters in the size range from n=1 to<br />
n=13 deposited on ultrathin ferromagnetic nickel and iron surfaces demonstrate the importance<br />
<strong>of</strong> the substrate. Whereas for Cr clusters on Ni films no XMCD signal is found, for Cr clusters<br />
on Fe films a strong decrease <strong>of</strong> the magnetic moment by a factor <strong>of</strong> 4 is found with increasing<br />
cluster size. This effect can be interpreted in terms <strong>of</strong> a non-collinear coupling <strong>of</strong> the magnetic<br />
moments within the cluster and relative to the surface [3]. Finally, first results on the magnetic<br />
properties <strong>of</strong> deposited 4d transition metal atoms and dimers (Ru, Mo) will be given .<br />
References<br />
[1] J.T. Lau , A. Föhlisch, R. Nietubyc, M. Reif, and W. Wurth, Phys. Rev. Lettl. 89, 057202 (2002).<br />
[2] J.T. Lau , A. Föhlisch, M. Martins, R. Nietubyc, M. Reif, and W. Wurth, New J. Of Phys. 4, 98.1<br />
(2002)<br />
[3] M. Reif, L. Glaser, M. Martins, W. Wurth, S. Lounis, and S. Blügel, in preparation.<br />
17
Emergent physics and chemistry <strong>of</strong> clusters: Fermion/boson clusters in<br />
quantum dots/traps, and nanocatalysis<br />
18<br />
U. Landman<br />
University School <strong>of</strong> Physics, Georgia Institute <strong>of</strong> Technology, Atlanta, Georgia 30332-0430, USA<br />
We discuss several physical and chemical cluster phenomena that are emergent in nature.<br />
Focus is placed on emergent symmetry-breaking physical processes resulting in formation <strong>of</strong><br />
electron crystalline clusters in 2D quantum dots, and on the breaking <strong>of</strong> trapped Bose-Einstein<br />
condensates into Bose quantum crystallites, occurring as the inter-atomic repulsion is increased.<br />
Emergent chemical cluster phenomena are discussed in the context <strong>of</strong> nanocatalysis by gold<br />
nanoclusters, with an emphasis on clusters supported on metal-oxide surfaces (specifically<br />
MgO), and the role <strong>of</strong> surface defects and cluster charging effects.
Cluster ferroelectricity<br />
Walt de Heer<br />
Georgia Institute <strong>of</strong> Technology<br />
Experiments on beams <strong>of</strong> isolated Nb, Ta, V, Al clusters with up to 200 atoms, show that<br />
these particles attain relatively large electric dipole moments at cryogenic temperatures. This<br />
ferroelectric property cannot be reconciled with normal metallic behavior since the ferroelectric<br />
state implies large internal electric fields. However various aspects <strong>of</strong> this state <strong>of</strong> matter appear<br />
to be closely related to bulk superconductivity. For example, the effect only occurs in metals<br />
that are superconductors in the bulk and a strong dependence even-odd alternation is observed.<br />
The ferroelectric transition temperature is similar to the bulk Tc. A survey <strong>of</strong> the electronic<br />
properties <strong>of</strong> these and other metallic clusters reinforce the superconducting pairing hypotheses<br />
in these clusters.<br />
19
20<br />
Molecular Magnets in the Gas Phase: Stern-Gerlach Beam Deflection<br />
Studies <strong>of</strong> Metal Clusters<br />
Mark B. Knickelbein<br />
Chemistry Division, CHM 200, Argonne National Laboratory, Argonne, Illinois 60439, USA<br />
The study <strong>of</strong> transition metal clusters in the gas phase <strong>of</strong>fers the opportunity to study the<br />
emergence <strong>of</strong> novel magnetic behavior atom-by-atom, in the size range that bridges atomic and<br />
bulk behavior. In this contribution, the results <strong>of</strong> Stern-Gerlach molecular beam deflection<br />
studies <strong>of</strong> transition metal clusters will be presented. Bare manganese clusters (Mn5-99) exhibit<br />
spatial deflections or broadening <strong>of</strong> magnitudes far in excess <strong>of</strong> those expected based on the<br />
susceptibility <strong>of</strong> bulk manganese, indicating that clusters in this size range are magnetically<br />
ordered. The magnitude <strong>of</strong> the magnetic moments (Figure 1), interpreted in light <strong>of</strong> recent<br />
density functional theory calculations, suggest that Mn clusters in this size range are molecular<br />
ferrimagnets. Recent magnetic deflection results for clusters composed <strong>of</strong> the Group IIIB<br />
metals, Scn, Yn, and Lan, indicate that they are also molecular magnets. Several Group IIIB<br />
clusters stand out as bona fide high-moment molecular magnets: Sc13 (6.0±0.2µb), Y8<br />
(5.2±0.1 µb), Y13 (9.6±0.1 µb), and La6 (4.8±0.2 µb).<br />
References<br />
moment per atom (µ b )<br />
2.0<br />
1.5<br />
1.0<br />
0.5<br />
0.0<br />
12<br />
13<br />
10 20 30 40 50 60 70 80 90 100<br />
Figure 1. Magnetic moments per atom for manganese clusters produced at 68K.<br />
[1] M. Knickelbein, Phys. Rev. Lett. 86, 5255 (2001).<br />
[2] M. Knickelbein, Phys. Rev. B 70, 014424 (2004).<br />
19<br />
n<br />
57<br />
Mn n
Oxidation Effects <strong>of</strong> the Small Chromium and Manganese Cluster<br />
Ions<br />
K. Tono, 1,2 A. Terasaki, 2 T. Ohta, 1 and T. Kondow 2<br />
1 Department <strong>of</strong> Chemistry, University <strong>of</strong> Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan<br />
2 Cluster Research Laboratory, Toyota Technological Institute in East Tokyo Laboratory, Genesis<br />
Research Institute, Inc., 717-86 Futamata, Ichikawa, Chiba 272-0001, Japan<br />
Properties <strong>of</strong> transition-metal clusters are affected by reaction with foreign elements such as<br />
nitrogen and oxygen. For example, it has been predicted that the magnetic property <strong>of</strong> a<br />
chromium dimer is drastically changed by either nitridation or oxidation [1,2]. Motivated by<br />
these theoretical studies, we investigated the electronic structures <strong>of</strong> the chromium- and<br />
manganese-oxide cluster anions through measurements <strong>of</strong> photoelectron spectra and analyses<br />
with the aid <strong>of</strong> the density functional theory (DFT). It was found that the spin magnetic moment<br />
<strong>of</strong> Cr2O – is as large as 9 µB, while that <strong>of</strong> Cr2 – is 1 µB. This result shows that the spin coupling<br />
between the chromium sites becomes ferromagnetic upon oxidation <strong>of</strong> Cr2 – whose chromium<br />
sites are coupled antiferromagnetically [3,4]. The mechanism <strong>of</strong> the ferromagnetic spin coupling<br />
is explained on the basis <strong>of</strong> the geometric and electronic structures obtained by the DFT<br />
calculations. The oxygen atom at the bridge site weakens the strong bond between the<br />
chromium atoms, which is responsible for the antiferromagnetic coupling in Cr2 – . In addition,<br />
significant hybridization between chromium 3d and oxygen 2p orbitals allows electrons in the<br />
same spin state to be transferred from the two chromium atoms to the oxygen atom.<br />
Consequently the local spins on the chromium sites are bound to form a ferromagnetic coupling<br />
in a similar scheme <strong>of</strong> the superexchange interaction encountered in solids. An oxidation effect<br />
<strong>of</strong> a similar kind was found for Mn2O – , in which a ferromagnetic coupling between the local<br />
spins (about 5.5 µB) at the manganese sites stabilizes its electronic structure [5,6].<br />
Manganese clusters differ distinctly from chromium clusters; the manganese atoms are very<br />
weakly bound because <strong>of</strong> the closed shell <strong>of</strong> 4s electrons. This is also true to singly charged<br />
manganese cluster cations, MnN + (N=3–7), where the binding energy is found to be less than 1<br />
eV/atom as reported in Ref. [7] and as shown further by the present measurements. The<br />
structural specificity results from a weak van-der-Waals like interaction between the constituent<br />
atoms, and is likely to change greatly if one introduces an oxygen atom into MnN + , because the<br />
oxygen could glue manganese atoms in its vicinity. Actually we elucidated how the introduced<br />
oxygen changes the geometrical and electronic structures <strong>of</strong> MnN + in photodissociation<br />
experiments <strong>of</strong> MnNO + (N=3–5). In practice, the mass spectra <strong>of</strong> photodissociation products<br />
from MnNO + were measured as a function <strong>of</strong> the photon energy <strong>of</strong> an excitation laser. The<br />
results show that the oxygen atom and two manganese atoms form a Mn2O + core ion and the<br />
other manganese atoms are weakly bound to the core ion. Analyses <strong>of</strong> the photodissociation<br />
action spectra <strong>of</strong> MnNO + are now in progress in order to obtain detailed information on the<br />
electronic and geometric structures.<br />
References<br />
[1] S. E. Weber, B. V. Reddy, B. K. Rao, and P. Jena, Chem. Phys. Lett. 295, 175 (1998).<br />
[2] B. V. Reddy and S. N. Khanna, Phys. Rev. Lett. 83, 3170 (1999).<br />
[3] K. Tono, A. Terasaki, T. Ohta, and T. Kondow, Phys. Rev. Lett. 90, 133402 (2003).<br />
[4] K. Tono, A. Terasaki, T. Ohta, and T. Kondow, J. Chem. Phys. 119, 11221 (2003).<br />
[5] K. Tono, A. Terasaki, T. Ohta, and T. Kondow, Chem. Phys. Lett. 388, 374 (2004).<br />
[6] S. N. Khanna, P. Jena, W.-J. Zheng, J. M. Nilles, and K. H. Bowen, Phys. Rev. B 69, 144418<br />
(2004).<br />
[7] A. Terasaki, S. Minemoto, and T. Kondow, J. Chem. Phys. 117, 7520 (2002).<br />
21
22<br />
Electronic structure and spin polarization <strong>of</strong> dilute magnetic<br />
semiconducting nanocrystals: a first principles approach<br />
Xiangyang Huang 1 , Adi Makmal 2 , James R. Chelikowsky 1 , and Leeor Kronik 2<br />
1 Department <strong>of</strong> Chemical Engineering and Materials Science and the Institute for the Advanced Theory<br />
<strong>of</strong> Information Materials, University <strong>of</strong> Minnesota, Minneapolis 55455, USA<br />
2 Department <strong>of</strong> Materials and Interfaces, Weizmann Institute <strong>of</strong> Science, Rehovoth 76100, Israel.<br />
Bulk dilute magnetic semiconductors have attracted considerable attention in recent years<br />
because they exhibit semiconducting and magnetic properties at the same time, potentially<br />
enabling novel electronic devices that manipulate the electron spin in addition to its charge,<br />
commonly known as “spintronic” devices. 1 Novel spintronic effects are expected at<br />
nanocrystalline dilute magnetic semiconductors because the carrier confinement greatly<br />
enhances spin-spin interactions.<br />
Here, we present what we believe to be the first ab initio study <strong>of</strong> the electronic structure <strong>of</strong> Mncontaining<br />
Ge, GaAs, and ZnSe nanocrystals, using a real-space pseudopotential-density<br />
functional theory approach. We find that in all cases significant spin-polarization is formed and<br />
that the magnetic moment distribution around the Mn atom displays clear chemical trends,<br />
becoming more localized with increasing bond ionicity, as shown in Fig. 1. A detailed analysis<br />
<strong>of</strong> the electronic structure reveals different patterns <strong>of</strong> level filling and ferromagnetic or antiferromagnetic<br />
couplings. Importantly, the electronic structure exhibits considerable quantum<br />
size effects. The electronic and magnetic properties <strong>of</strong> the dilute magnetic nanocrystals are<br />
compared and contrasted with the properties <strong>of</strong> the corresponding bulk systems. Potential device<br />
implications are discussed.<br />
References<br />
Figure 1. Distribution <strong>of</strong> the net magnetic moment for (from left to right)<br />
passivated MnGe81,MnGa40As41, and MnZn40Se41 nanocrystals.<br />
[1] S. A. Wolf, D. D. Awschalom, R. A. Buhrman, J. M. Daughton, S. von Molnar, M. L. Roukes A.<br />
Y. Chtchelkanova, and D. M. Treger, Science 294, 1488 (2001).
Electronic structure and bonding in gold coated silica cluster: a nano<br />
bullet for tumor<br />
Q. Sun, Q. Wang, and P. Jena<br />
Physics Department, Virginia Commonwealth University, Richmond, VA 23284, USA.<br />
Recently an exciting application <strong>of</strong> gold coated silica nano-shells has been found in treating<br />
tumor and cancer. The nano-shell consists <strong>of</strong> silica (SiO2) core <strong>of</strong> order 100 nm coated with<br />
about 20 nm <strong>of</strong> gold. It absorbs near infrared light (NIR) and converts that light to heat, causing<br />
irreversible thermal cellular destruction. When the nano-shells were incorporated into human<br />
breast cancer cells in a test tube, and then exposed to NIR, 100 percent <strong>of</strong> the cancer cells were<br />
killed. Motivated by this experiment we have investigated the coating <strong>of</strong> a small silica cluster<br />
(<strong>of</strong> the order <strong>of</strong> a few nano-meters) with Au to understand (1) if such a small cluster can absorb<br />
infrared radiation and (2) if so, does the mechanism for such absorption have electronic origin?<br />
(3) How do Au atoms bind with silica core? We show for the first time that gold atoms bind to<br />
silicon atoms with dangling bonds and serve as seeds for the growth <strong>of</strong> Au islands (Fig. 1a). The<br />
large electron affinity <strong>of</strong> gold causes significant change in the electronic structure <strong>of</strong> silica<br />
resulting in a substantial reduction in the HOMO-LUMO gap (Fig. 1 b), thus allowing it to<br />
absorb near infrared radiation (Fig. 1 c). Our study suggests that a small cluster can have similar<br />
functionality in the treatment <strong>of</strong> cancer as the large size nano-shell, but for a different<br />
mechanism. The advantage <strong>of</strong> such small nano-bullet for targeting tumor and cancer is that it<br />
can easily penetrate the crowded environments such as the biological milieu <strong>of</strong> cells and live<br />
tissues for effective drug delivery.<br />
Au<br />
Au<br />
References<br />
Geometry<br />
O<br />
Si<br />
Au<br />
Energy (eV)<br />
(a) (b) (c)<br />
Figure 1. (a) Geometry, (b) HOMO-LUMO gap, and (c) optical spectra <strong>of</strong> Au 3-(SiO 2) 3.<br />
[1] L.R. Hirsch, et al. PNAS 100 , 13549 (2003).<br />
[2] Q. Sun, Q. Wang, B.K. Rao, and P. Jena, Phys. Rev. Lett. 93, 186803 (2004).<br />
1<br />
0<br />
-1<br />
-2<br />
-3<br />
-4<br />
-5<br />
-6<br />
-7<br />
-8<br />
-9<br />
-10<br />
-11<br />
(SiO 2 ) 3<br />
Au 3 -(SiO 2 ) 3<br />
Energy spectra<br />
Optical absorption (arb.units)<br />
7<br />
6<br />
5<br />
4<br />
3<br />
2<br />
1<br />
Optic spectra<br />
0<br />
0 100 200 300 400 500 600 700 800 900 1000<br />
Wave length (nm)<br />
23
24<br />
Low-temperature Oxidation <strong>of</strong> N2 on Supported Tungsten<br />
Nanoclusters<br />
Junichi Murakami 1 , Wataru Yamaguchi 2<br />
1 Nanotechnology Research Institute, National Institute <strong>of</strong> Advanced Industrial<br />
Science and Technology, Central 4, 1-1-1 Higashi, Tsukuba, 305-8562, Japan<br />
2 Materials Research Institute for Sustainable Development, National Institute <strong>of</strong><br />
Advanced Industrial Science and Technology, 2266-98 Anagahora, Shidami,<br />
Moriyama-ku, Nagoya, 463-8560, Japan<br />
It is known that enzymes in organisms <strong>of</strong>ten contain nanoclusters composed <strong>of</strong> several<br />
transition-metal atoms and sulfur or oxygen atoms. One <strong>of</strong> the famous examples <strong>of</strong> such<br />
enzymes is the nitrogenase that carry out nitrogen fixation (conversion <strong>of</strong> N2 in air into<br />
ammonia) at room temperature and 0.8 atm. Nitrogenase is known to carry several kinds <strong>of</strong><br />
nanoclusters, among which FeMo cluster (MoFe7S9) is believed to be most important for<br />
activation and reduction <strong>of</strong> N2 at room temperature. The fact that the nanocluster-containing<br />
enzymes carry out otherwise difficult chemical reactions suggests the nanoclusters are exotic<br />
materials that can catalyze the reactions under mild conditions.<br />
We recently started studying reactions <strong>of</strong> N2 on deposited transition-metal nanoclusters to<br />
investigate whether they also have such catalytic activities. Size-selected tungsten nanoclusters<br />
(Wn;n=2-6) are s<strong>of</strong>tlanded at room temperature on graphite (HOPG) surfaces that were<br />
bombarded by Ar+ ions before the cluster deposition. Defects created by the ion bombardment<br />
work as pinning centers for the clusters. The deposited nanoclusters are exposed to various<br />
gases and chemical reactions <strong>of</strong> N2 on the clusters were investigated.<br />
When the clusters at 140K were exposed simultaneously to N2 and H2O, it was found that N2O<br />
forms on the clusters. This was observed by X-ray photoelectron spectroscopy(XPS) and<br />
confirmed by thermal desorption spectroscopy(TDS). TDS measurements using isotopemers <strong>of</strong><br />
N2 and H2O revealed that N2, activated on the clusters, reacted with an O atom from H2O to<br />
form N2O at a temperature as low as 140K. The details including cluster-size dependence <strong>of</strong> the<br />
reaction will be presented at the symposium.<br />
References<br />
[1] W.Yamaguchi and J.Murakami, Chem. Phys. Lett. 378, 521 (2003).
Catalytic CO oxidation on ionic platinum clusters<br />
O. Petru Balaj, Iulia Balteanu, Tobias Roßteuscher, Vladimir E. Bondybey, Martin K. Beyer<br />
Department Chemie, Physikalische Chemie 2, Technische <strong>Universität</strong> München, Lichtenbergstraße 4,<br />
85747 Garching, Germany<br />
Cationic and anionic platinum clusters with up to 25 atoms are produced from isotopically<br />
highly enriched platinum-195 ( 195 Pt, 97.28%) in a laser vaporization source, and their reactions<br />
are investigated by Fourier transform ion cyclotron resonance mass spectrometry. For certain<br />
clusters, depending on both charge state and size, efficient catalytic conversion <strong>of</strong> CO and N2O<br />
to CO2 and N2 is observed. If N2O is present in sufficient excess, the catalytic cycle shown in<br />
Figure 1 for Pt7 + is running continuously. Poisoning occurs by adsorption <strong>of</strong> several CO<br />
molecules, and can be suppressed by increasing the N2O pressure in the ICR cell. All clusters<br />
containing more than five platinum atoms readily adsorb CO, while the reactivity with N2O is<br />
strongly size-dependent [1]. Efficient catalytic conversion <strong>of</strong> CO is observed only for those<br />
clusters which react efficiently with N2O [2].<br />
Figure 1. Catalytic cycle <strong>of</strong> CO oxidation with N 2O on Pt 7 + as a catalyst. Pt7 + , Pt7O + , Pt 7O 2 + as well as Pt7CO + are<br />
active species in the catalytic cycles. Upon addition <strong>of</strong> a second CO molecule to Pt 7CO + , the efficiency <strong>of</strong> the<br />
oxidation reaction is significantly reduced, additional CO molecules poison the cluster. CO adsorption stops when<br />
Pt 7CO 10 + is reached.<br />
References<br />
[1] I. Balteanu, O. P. Balaj, M. K. Beyer, V. E. Bondybey, Phys. Chem. Chem. Phys. 6, 2910 (2004).<br />
[2] O. P. Balaj, I. Balteanu, T. T. J. Roßteuscher, M. K. Beyer, V. E. Bondybey, Angew. Chem. in<br />
print.<br />
25
26<br />
Cluster Reactions and Properties: Laying the Foundation for Cluster<br />
Assembled Materials<br />
A. W. Castleman Jr.<br />
Departments <strong>of</strong> Chemistry and Physics, Penn State University, University Park, PA 16802<br />
Currently, there is extensive interest in systems <strong>of</strong> finite size as they <strong>of</strong>ten give rise to<br />
unique properties that differ from those <strong>of</strong> an extended solid or the individual molecular<br />
constituents <strong>of</strong> which they are comprised. Particularly interesting are nanoscale systems whose<br />
composition can be selectively chosen, and ones whose individual characteristics can be<br />
retained when assembled as an extended material. A major long-term goal <strong>of</strong> our research in this<br />
area is to develop ways <strong>of</strong> tailoring the design and formation <strong>of</strong> new nanoscale materials <strong>of</strong><br />
chosen electronic and catalytic properties. Recent success has been obtained in producing alloy<br />
cluster species <strong>of</strong> specific size and composition that simulate various elements <strong>of</strong> the periodic<br />
table.<br />
As a complementary approach to conventional surface studies widely used in the field <strong>of</strong><br />
catalysis, it is becoming increasingly recognized that cluster science can help elucidate the<br />
physical and chemical properties <strong>of</strong> condensed phase catalysts and, can provide detailed<br />
information on the mechanisms <strong>of</strong> reactions and the nature <strong>of</strong> various reaction sites that enables<br />
certain catalytic materials to be especially effective. In addition, the possible direct use <strong>of</strong><br />
clusters as catalysts has aroused interest due to the difference in reactivities <strong>of</strong>ten observed for<br />
nanoscale materials compared to conventional bulk catalysts. Our latest findings on mass<br />
selected transition metal oxides, carbon containing, and metallic clusters will be presented. In<br />
related studies, we are employing femtosecond pump-probe techniques to explore the electronic<br />
properties <strong>of</strong> the clusters, including their excitation and relaxation behavior, which is providing<br />
insights into their evolving band structure. Findings pertaining to the electronic characteristics<br />
<strong>of</strong> metal-carbon systems and efforts to obtain deposits <strong>of</strong> mass selected species will also be<br />
discussed.
Melting, Pre-melting, and Glass Transitions in Gallium and Aluminum<br />
Clusters<br />
G.A. Breaux, B. Cao, C.M. Neal, and M. F. Jarrold<br />
Department <strong>of</strong> Chemistry, Indiana University, 800 East Kirkwood Avenue, Bloomington, Indiana 47405-<br />
7102, USA<br />
The melting <strong>of</strong> gallium and aluminum clusters with between 10 and 70 atoms has been<br />
examined using multicollision induced dissociation (MCID) calorimetry measurements and high<br />
temperature ion mobility measurements. A first order melting transition is indicated by a spike<br />
in the heat capacity due to the latent heat and an abrupt change in the average collision cross<br />
section due to a change in the volume or shape <strong>of</strong> the cluster when it melts. For some aluminum<br />
clusters (e.g. Al51 + and Al52 + ) the peaks in the heat capacity are bimodal suggesting the presence<br />
<strong>of</strong> a pre-melting transition where the surface <strong>of</strong> the cluster melts before the core. While premelting<br />
transitions are present in many simulations <strong>of</strong> cluster melting, this is the first time they<br />
have been observed experimentally. For some gallium clusters, the collision cross sections<br />
suggest that a melting transition occurs while there is no peak in the heat capacity. This is the<br />
signature for a glass transition which has been predicted to occur for some cluster sizes in<br />
several recent simulations. A glass transition occurs for clusters which are intrinsically<br />
amorphous - clusters that do not have a well-defined geometry.<br />
27
Phase Transition and Phase Coexistence in Atomic Clusters and Other<br />
Mesoscopic Systems<br />
28<br />
Mihai Horoi, Koblar Alan Jackson<br />
Department <strong>of</strong> Physics, Central Michigan University, Mount Pleasant, Michigan 48859, USA<br />
We investigate signatures <strong>of</strong> shape transition and shape coexistence phases in small atomic<br />
clusters and other mesoscopic systems, such as the atomic nuclei. One <strong>of</strong> the best know example<br />
is the prolate-compact shape transition/coexistence phenomena observed in the mobility<br />
experiments <strong>of</strong> Si clusters.[2] Using a hierarchical strategy that features an extensive tightbinding-based<br />
search <strong>of</strong> the energy surface, followed by a full density functional theory<br />
investigation <strong>of</strong> the most stable structures, we have determined the lowest-energy clusters across<br />
the range n=2 to 28.[3] The calculated properties <strong>of</strong> these clusters are in very good agreement<br />
with available measurements <strong>of</strong> dissociation energies, ionization energies and ion mobilities,<br />
providing strong evidence that these structures are the ones found in experiments. The<br />
calculations clearly exhibit a transition in the relative stability <strong>of</strong> prolate and compact clusters<br />
between n=25 and 26, coinciding exactly with the experimental behavior. The lowest energy<br />
prolate and compact structures are found almost degenerate, justifying the coexistence <strong>of</strong> shapes<br />
observed in the experiment. The binding energy per atom <strong>of</strong> the ground states vs N -1/3 exhibits a<br />
long plateau in the transition/coexistence region (see Fig.), suggesting that this phenomena may<br />
be related to a relative s<strong>of</strong>t surface tension. Similar behavior was recently found in the isotope<br />
152 <strong>of</strong> the nucleus <strong>of</strong> the element Sm, for which the ground sate, J π = 0 + , is known to be very<br />
deformed (oblate), and the first excited J π = 0 + , is compact. A similar signature in the binding<br />
energy per atom <strong>of</strong> the Sm isotopes can also be extracted from the available experimental data.<br />
Figure 1. Shape transition and shape coexistence signature in the binding energy per atom <strong>of</strong> Si clusters. Figure taken<br />
from Ref. [1], but red dots are the results <strong>of</strong> our simulations (Ref. [3]).<br />
References<br />
[1] T. Bachels and R. Schaefer, Chem. Phys. Lett. 324, 356 (2000).<br />
[2] R.R. Hudgins, I. Motoharu, and M.F. Jarrold, J. Chem. Phys. 111, 7865 (1999).<br />
[3] A.K. Jackson, M. Horoi, I. Chaudhuri, Th. Fraunheim, and A. A. Shvartsburg, Phys. Rev. Lett. 93,<br />
013401 (2004).
Vibrational Spectroscopy <strong>of</strong> Large Sodium Doped Water Clusters:<br />
Size Selection by Ionization-Vibration Coupling<br />
Christ<strong>of</strong> Steinbach, Udo Buck<br />
Max-Planck-Institut für Strömungsforschung, Bunsenstrasse 10, 37073 Göttingen, Germany<br />
One way to solve the problem <strong>of</strong> measuring reliable size distributions <strong>of</strong> weakly bound<br />
clusters is to dope the clusters with one sodium atom and to ionize the system by a single<br />
photon close to the threshold. 1,2 In this contribution we have extended this method to obtain<br />
complete size selection. This is achieved by coupling the UV radiation <strong>of</strong> a dye laser below the<br />
ionization threshold with the tunable infrared radiation <strong>of</strong> an optical parametric oscillator. The<br />
procedure works provided that there is sufficient coupling between the vibrational and the<br />
electronic motion <strong>of</strong> the ionization.<br />
We have applied this method to the measurement <strong>of</strong> the vibrational OH-stretch spectra <strong>of</strong><br />
Na(H2O)n clusters in the size range from n=8 to 80. The spectra are dominated by intensity<br />
peaks around 3400 cm -1 which we attribute to an increased transition dipole moment <strong>of</strong><br />
delocalized electrons which have been observed in calculations for this type <strong>of</strong> clusters. 3 The<br />
spectral features are discussed and compared with those obtained for pure water clusters 4 and<br />
water clusters doped with sodium ions. 5<br />
References<br />
[1] S. Schütte and U. Buck, Int. J. Mass. Spectrom. 220, 183 (2002).<br />
[2] C. Bobbert, S. Schütte, C. Steinbach, and U. Buck, Eur. Phys. J. D Journal 19, 183 (2002).<br />
[3] C. J. Mundy, J. Hutter, and M. Parrinello, J. Am. Chem. Soc. 122, 4837 (2000).<br />
[4] C. Steinbach, P. Andersson, J. K. Kazimirski, U. Buck, V. Buch, and T.A. Beu,<br />
J. Phys. Chem. A 108, 6165 (2004).<br />
[5] F. Schulz and B. Hartke, Phys. Chem. Chem. Phys. 5, 5021 (2004).<br />
29
30<br />
Novel elongated Chevrel-type (Mo3S3)nS2 clusters<br />
Gotthard Seifert and Sibylle Gemming<br />
Institut f. Physikalische Chemie, Technische <strong>Universität</strong>Dresden, D-01062 Dresden, Germany<br />
Clusters <strong>of</strong> the composition Mo3nS3n+2 can be regarded as building blocks <strong>of</strong> the<br />
corresponding sulfur-based Chevrel phases [1]. These compounds are generally built from equal<br />
amounts <strong>of</strong> two Mo3nS3n+2 species with different values <strong>of</strong> n, thus the overall formula unit <strong>of</strong> the<br />
network is Mo3nS3n+4. For the alkali metals as counter ions the charge state <strong>of</strong> the single cluster<br />
building block is -1. Thus, the clusters in these compounds occur in the same charge state as the<br />
free clusters recently observed by experimental studies [2].<br />
The cluster series up to n = 9 was investigated by density-functional-based calculations. Both<br />
the neutral and the anionic species were investigated. All structures up to Mo21S23 exhibit a<br />
HOMO-LUMO gap <strong>of</strong> about 0.5 eV. The relative stability <strong>of</strong> the neutral clusters shows a weak<br />
even-odd-alternation, which roughly correlates with the HOMO-LUMO spacings. The relative<br />
stabilities <strong>of</strong> the different members <strong>of</strong> the cluster sequence are highly dependent on the charge<br />
state, i.e. on the number and type <strong>of</strong> counter ions in a solid phase. For comparison the infinitely<br />
long [Mo6S6] n chain was investigated by DFT band structure calculations, employing periodic<br />
boundary conditions.<br />
Calculated I-V curves fur such clusters show that the quasi one-dimensional Chevrel-type<br />
structures are promising candidates for nanoelectronic devices.<br />
Figure 1. Chevrel type structures <strong>of</strong> the Mo6S8 , Mo9S11 , Mo18S20 clusters and part <strong>of</strong> an infinite chain <strong>of</strong> a Chevrel<br />
structure (left to right, black Mo atoms ).<br />
References<br />
[1] D. Salloum, R. Gautier, P. Gougeon, M. Potel, J. Solid. State Chem. 177, 1672 (2004).<br />
[2] N. Bertram , Y.D. Kim, G. Ganteför, to be published
Novel Properties <strong>of</strong> S<strong>of</strong>t-Nano-Molecular Clusters<br />
Koji Kaya 1 , Atsushi Nakajima and Masaaki Mitsui 2<br />
1 Discovery Institute, RIKEN, Wako, 351-0198 Saitama, Japan<br />
2 Department <strong>of</strong> Chemistry, Keio Uinversity, Hiyoshi, Yokohama, Japan<br />
Over the past 20 years, our group at Keio University has devoted to the development <strong>of</strong><br />
new material science in nao-size regime on the basis <strong>of</strong> small molecules and metal atoms.<br />
Several new findings have been already reported. However , these reports have been restricted<br />
to relatively small size clusters with mass number less than several hundreds. Recently we have<br />
succeeded in the synthesis <strong>of</strong> relatively large sized molecular clusters <strong>of</strong> aromatic molecules<br />
such as benzene, naphthalene and anthracene. From the photoelectron spectra <strong>of</strong> anion clusters<br />
<strong>of</strong> these molecules as shown in the figure, we found peculiar behavior <strong>of</strong> the clusters in the mid<br />
size range where ordered and disordered electronic properties coexists. We will discuss this<br />
subject.<br />
Then, discussin will extends to the post nanoscience project which will be conducted under the<br />
collaboration <strong>of</strong> several national organizations including RIKEN. The project focuses attention<br />
on the synthesis and understanding the mechanism <strong>of</strong> novel bio-miemetic materials by the<br />
collaboration among chemists, bio-scientists and information physicists.<br />
Photoelectron Spectra <strong>of</strong> Size Selected Anthracene Cluster<br />
Anions<br />
II<br />
I<br />
II<br />
I<br />
31
32<br />
Melting <strong>of</strong> Sodium Clusters: Where Do the Magic Numbers Come<br />
from?<br />
H. Haberland, T. Hippler, J. Donges, O. Kostko, M. Schmidt, and B. v. Issendorff<br />
Fakultät für Physik, <strong>Universität</strong> Freiburg, H.Herderstr. 3, 79104 Freiburg, Germany<br />
Melting temperatures <strong>of</strong> Na clusters show size-dependent fluctuations that have resisted<br />
interpretation so far. It will be discussed that these temperatures, in fact, cannot be expected to<br />
exhibit an easily understandable behavior. The energy and entropy differences between the<br />
liquid and the solid clusters turn out to be much more relevant parameters. They exhibit<br />
pronounced maxima that correlate well with geometrical shell closings, demonstrating the<br />
importance <strong>of</strong> geometric structure for the melting process. Icosahedral symmetry dominates, a<br />
conclusion corroborated by new photoelectron spectra measured on cold cluster anions. In the<br />
vicinity <strong>of</strong> the geometrical shell closings the measured entropy change upon melting is in good<br />
agreement with a simple combinatorial model.
Posters<br />
33
Carbon<br />
35
Structure and Bonding in Carbon Clusters C14 to C60<br />
Jeongeon Park, Jihye Shim, and Eok Kyun Lee<br />
Department <strong>of</strong> Chemistry, Korea Advanced Institute <strong>of</strong> Science and Technology, 373-1, Guseong-dong,<br />
Yuseong-gu, Deajeon, 305-701, Republic <strong>of</strong> Korea<br />
B - 1<br />
Density functional calculations have been applied to study various isomers <strong>of</strong> neutral carbon<br />
clusters C2n( 7 ≤ n ≤ 30 ) using both local spin density and generalized gradient approximations<br />
for the exchange-correlation energy. The structures <strong>of</strong> stable isomers include chains, rings,<br />
cages, and graphitic structures. We examined the most stable structure for each cluster <strong>of</strong><br />
various size and found a specific tendency as the size changes. Cage structure is the most stable<br />
structure for n≥16. We observed a fourfold periodicity in the monocyclic ring structures. Small<br />
effect <strong>of</strong> spin-polarization was observed in the monocyclic rings and the graphitic isomers with<br />
n = 4k( k = 1, 2, 3, ....). We calculated the ionization energy and the cohesive energy for the<br />
cage structures, and compared with previous results. All structures have been fully relaxed by ab<br />
initio molecular dynamics combined with simulated annealing, and the change <strong>of</strong> the<br />
trajectories <strong>of</strong> each atomic coordinate during the structure relaxation has been recorded . We<br />
further examined the characteristic features <strong>of</strong> the electronic structure <strong>of</strong> each isomer.<br />
References<br />
[1] R.O. Jones and G.Seifert, Phys. Rev. Lett. 79, 443 (1997).<br />
[2] G. Seifert, K. Vietze and R. Schmidt, eJ. Phys. B: At. Mol. Opt. Phys. 29, 5183 (1996).<br />
37
38<br />
B - 2<br />
High Resolution Measurements <strong>of</strong> Fullerenes and Endohedrals<br />
K. Głuch 2 , S. Matt-Leubner 1 , S. Feil 1 , O. Echt 3 , C. Lifshitz 4 , S. Denifl 1 , S. Ptasinska 1 , B. Concina 5 , P.<br />
Scheier 1 , and T. D. Märk 1<br />
1 Institut für Ionenphysik, Leopold Franzens <strong>Universität</strong>, A-6020 Innsbruck Austria<br />
2 Institute <strong>of</strong> Mathematics, Physics and Informatics Marie Curie-Sklodowska University, Lublin, Poland<br />
3 University <strong>of</strong> New Hampshire, Durham, New Hampshire, USA<br />
4 The Hebrew University <strong>of</strong> Jerusalem, Jerusalem, Israel<br />
5 Department <strong>of</strong> Physics and Astronomy, University <strong>of</strong> Aarhus, Denmark<br />
The stability <strong>of</strong> fullerenes has been a controversial topic for some time. The (adiabatic)<br />
dissociation energies for the preferred dissociation reactions <strong>of</strong> isolated (gas-phase) fullerenes<br />
Cn → Cn-2 +C2 cannot be derived from measured thermodynamic quantities, not even for n = 60<br />
or 70. There is also a growing interest in fullerenes <strong>of</strong> sizes larger and smaller than C60 and C70.<br />
We have measured the kinetic energy released in the unimolecular dissociation <strong>of</strong> fullerene ions,<br />
Cn+ → Cn-2+ + C2, for sizes 42 ≤ n ≤ 90 [1]. A three sector field mass spectrometer equipped<br />
with two electrostatic sectors has been used in order to ensure that contributions from<br />
isotopomers (same n but containing 13C) do not distort the experimental kinetic energy release<br />
distributions. We apply the concept <strong>of</strong> microcanonical temperature to derive from these data the<br />
dissociation energies <strong>of</strong> fullerene cations. They are converted to dissociation energies <strong>of</strong> neutral<br />
fullerenes with the help <strong>of</strong> published adiabatic ionization energies. The results are compared<br />
with literature values.<br />
The fascinating possibility <strong>of</strong> caging atoms was noticed immediately by Kroto et al when they<br />
proposed the hollow icosahedral structure <strong>of</strong> C60. The kinetic stability <strong>of</strong> endohedrals under<br />
ambient conditions has originally presented some puzzles. We have measured the kinetic energy<br />
release distributions for unimolecular C2 loss from singly and multiply charged Sc3N@C78z+<br />
(z=1,2) and Sc3N@C80z+ (z=1,2,3) [2]. Using finite heat bath theory we have deduced the<br />
dissociation energies <strong>of</strong> these endohedral ions toward loss <strong>of</strong> C2. The data show that the<br />
complexation energies i. e. the adiabatic binding energies between Sc3N and the fullerene cage<br />
Cnz+ are, for a given charge state and within the experimental uncertainty, identical for n = 76,<br />
78 and 80.<br />
Formation <strong>of</strong> negative fullerene ions, especially <strong>of</strong> C60–, has been a contentious issue over the<br />
last decade. We try to clarify the mystery <strong>of</strong> the zero energy peak <strong>of</strong> the negative C60 with the<br />
help <strong>of</strong> a specially dedicated electron monochromator instrument. Moreover we compare for the<br />
first time experimental data <strong>of</strong> negative empty cage fullerenes and endohedrals.<br />
References<br />
[1] K. Gluch, S. Matt Leubner, O. Echt, B. Concina, P. Scheier, and T.D. Märk, High-resolution<br />
kinetic energy release distributions and dissociation energies for fullerene ions Cn+, 42
Photoelectron Spectroscopy <strong>of</strong> Fullerene Dianions C76 2- , C78 2- and C84 2-<br />
Oli T. Ehrler 1 , Filipp Furche 2 , J. Mathias Weber 1 , and Manfred M. Kappes 1<br />
B - 3<br />
1 Institut für Physikalische Chemie mikroskopischer Systeme, <strong>Universität</strong> Karlsruhe (TH), Kaiserstrasse<br />
12, Karlsruhe, D-76128, Germany<br />
2 Institut für Physikalische Chemie, Theoretische Chemie, <strong>Universität</strong> Karlsruhe (TH), Kaiserstrasse 12,<br />
Karlsruhe, D-76128, Germany<br />
In the past years, investigations <strong>of</strong> multiply negatively charged anions (MCAs) have<br />
become a research field <strong>of</strong> their own. MCAs should obey a particular high degree <strong>of</strong> electron<br />
correlation to minimize Coulomb repulsion between the excess charges, which are no longer<br />
screened due to the overall neutral core and are thus an interesting benchmark system for<br />
theoretical chemists. Moreover, long-range Coulomb interaction between an outgoing electron<br />
and the still negatively charged core leads to a significantly different photodetachment threshold<br />
law than Wigner’s law for monoanions due to the formation <strong>of</strong> the repulsive Coulomb barrier<br />
(RCB), which can kinetically hinder the decay <strong>of</strong> excited MCAs and even stabilize metastable<br />
MCAs with respect to electron emission.<br />
Due to their high symmetry and available wide size distribution maintaining a similar<br />
morphologic pattern, multiply negatively charged fullerenes are a particularly suitable target to<br />
study size evolution effects in MCAs. In the present work [1,2], we report laser photoelectron<br />
spectra <strong>of</strong> the doubly negatively charged fullerenes C76 2- , C78 2- and C84 2- at 2.33 eV, 3.49 eV, and<br />
4.66 eV photon energy. From these spectra, second electron affinities and vertical detachment<br />
energies, as well as estimates for the RCBs are obtained. These results are discussed in the<br />
context <strong>of</strong> electrostatic models. They reveal that fullerenes are similar to conducting spheres,<br />
with electronic properties scaling with their size. The experimental spectra are compared with<br />
the accessible excited states <strong>of</strong> the respective singly charged product ions calculated in the<br />
framework <strong>of</strong> time dependent density functional theory (TDDFT).<br />
Figure 1. Size dependence <strong>of</strong> AEA 2 values for fullerenes.<br />
Black squares: Spectroscopic data with experimental uncertainty. Open squares/circles: upper/lower limit for AEA 2<br />
(fully correlated point charges, dielectrically shielded vs. uncorrelated delocalized charges, w/o dielectric shielding);<br />
open triangles: AEA2 values obtained from a scalable model (see [1]).<br />
References<br />
[3] O.T. Ehrler, J.M. Weber, F. Furche, and M.M. Kappes, Phys. Rev. Lett. 91, art. no. 113006 (2003).<br />
[4] O.T. Ehrler, F. Furche, J.M. Weber, and M.M. Kappes, J. Chem. Phys. — accepted.<br />
39
40<br />
B - 4<br />
Radiative Cooling <strong>of</strong> Fullerenes and Endohedral Fullerenes<br />
Martin Hedén, Fredrik Jonsson, Elin Rönnow, Andrei Gromov, Klavs Hansen, Eleanor E. B. Campbell<br />
Department <strong>of</strong> Physics, Göteborg University, SE-41296 Göteborg, Sweden<br />
One <strong>of</strong> the interesting properties <strong>of</strong> the fullerenes is that, due to the similarity between their<br />
binding energies and ionisation potentials, excited molecules have decay channels in which the<br />
neutral fragmentation competes with delayed ionisation. An additional competing channel is<br />
that <strong>of</strong> radiative decay. In order to be able to extract reliable information from experiments<br />
concerning the binding energies <strong>of</strong> the molecules it is essential to understand the various<br />
competing mechanisms and have a consistent picture <strong>of</strong> the behaviour <strong>of</strong> these highly excited<br />
molecules. In this presentation we return to the determination <strong>of</strong> the radiative cooling <strong>of</strong><br />
fullerene ions as determined by time-<strong>of</strong>-flight experiments [1]. We compare the extracted<br />
product <strong>of</strong> emissivity and dissociation energy from experiments in which the starting molecule<br />
is different. In particular, we were interested in comparing the emissivity <strong>of</strong> an endohedral<br />
fullerene (in this case La@C82) with empty fullerenes. The data is displayed in Fig. 1 and<br />
compared with earlier data from C60 and more recent data from the Århus group [2]. Rather<br />
good agreement is obtained between the different data sets for the small fullerenes with a<br />
substantially higher scatter in the points for the larger molecules. However, we note that there is<br />
no significant difference in the emissivity <strong>of</strong> the endohedral fullerene compared with that <strong>of</strong> the<br />
empty fullerenes. The experimental details and assumptions will be presented and results will be<br />
discussed in the context <strong>of</strong> a simple model to describe the radiative cooling.<br />
εD 3<br />
2.0<br />
1.8<br />
1.6<br />
1.4<br />
1.2<br />
1.0<br />
0.8<br />
0.6<br />
0.4<br />
0.2<br />
0.0<br />
40 44 48 52 56 60 64 68 72 76 80 84<br />
Figure 1. Product <strong>of</strong> emissivity and the cube <strong>of</strong> the dissociation energy, extracted from time-<strong>of</strong>-flight data for<br />
different parent molecules. The full squares are data obtained from C60, C70 or C84 starting molecules. The empty<br />
squares are starting from La@C82. Full circles are early data from [1]. Empty circles are extracted from data given<br />
by [2].<br />
References<br />
[1] K. Hansen and E.E.B. Campbell, J. Chem. Phys., 104 5012 (1996).<br />
[2] S. Tomita et al., Phys. Rev. Lett. 87 073401 (2001)<br />
N
Nucleation <strong>of</strong> single-walled carbon nanotubes on catalyst particles:<br />
MD and electronic structure calculations<br />
Arne Rosén 1, 1, 2<br />
, Feng Ding and Kim Bolton<br />
1 Experimental Physics, School <strong>of</strong> Physics and Engineering Physics, Göteborg University and Chalmers<br />
University <strong>of</strong> Technology, SE-412 96, Göteborg, Sweden<br />
2 School <strong>of</strong> Engineering, University College <strong>of</strong> Borås, SE-50190, Borås Sweden<br />
B - 5<br />
Metal catalyzed single-walled carbon nanotube (SWNT) nucleation was studied by classical<br />
molecular dynamics (MD) and electronic structure theory. The simulations revealed the atomiclevel<br />
mechanism for SWNT nucleation on metal catalyst particles. The SWNTs nucleate<br />
between 800 - 1400 K, [1] which is the same temperature interval used for chemical vapor<br />
deposition (CCVD) experiments. Also, in agreement with experimental results the nucleated<br />
SWNT has the same diameter as the catalyst particle [2]. The studies also show that a highly<br />
supersaturated carbon concentration in the catalyst particle is needed to initiate the nucleation<br />
process. [1] Based on the simulations a detailed Vapor-Liquid-Solid (VLS) growth model was<br />
developed for both liquid and solid catalyst particles. [1, 3] Furthermore, MD and electronic<br />
structure theory studies indicate that the catalyst particle must be able to maintain an open end<br />
<strong>of</strong> the growing SWNT in order to be suitable for growth.<br />
References:<br />
[1] F. Ding, K. Bolton and A. Rosén, J. Phys. Chem. B, 108, 17369-17377 (2004).<br />
[2] F. Ding, A. Rosén, and K. Bolton, J. Chem. Phys. 121, 2775-2779 (2004).<br />
[3] F. Ding, A. Rosen, and K. Bolton, Chem. Phys. Lett. 393, 309-313 (2004).<br />
41
42<br />
B - 6<br />
Sphere currents in fullerenes<br />
Mikael P. Johansson, Dage Sundholm, Jonas Jusélius, Juha Vaara<br />
Department <strong>of</strong> Chemistry, University <strong>of</strong> Helsinki, P. O. Box 55, FI-00014 Helsinki, Finland<br />
We investigate the magnetically induced electric currents in fullerenes, using the newly<br />
developed GIMIC methodology [1]. With GIMIC, a quantitative measure <strong>of</strong> the current<br />
strengths can, for the first time, be obtained. A remarkable difference between neutral<br />
Buckminsterfullerene and its spherically aromatic [2] +10 cation is revealed. In both, uniform<br />
three-dimensional currents, circling the fullerenes are induced. In C60, these sphere currents are<br />
oppositely directed; the exohedral diamagnetic and endohedral paramagnetic currents to a large<br />
extent cancel, resulting in global non-aromaticity. C60 10+ , on the other hand, supports a<br />
unidirectional, global diamagnetic current <strong>of</strong> significant strength, consistent with spherical<br />
aromaticity. These global sphere currents should be considered the defining feature <strong>of</strong><br />
aromaticity in fullerenes [3]. The stabilising effect <strong>of</strong> spherical aromaticity is discussed in<br />
connection with the recently postulated all-golden fullerene, Au32 [4]. Spherical aromaticity is<br />
found to be <strong>of</strong> crucial importance for the stability <strong>of</strong> the species.<br />
References<br />
Figure 1. From left to right: Au 32; sphere currents; C 60.<br />
[1] J. Jusélius, D. Sundholm, J. Gauss, "Calculation <strong>of</strong> current densities using gauge-including atomic<br />
orbitals", J. Chem. Phys. 121, 3952 (2004).<br />
[2] A. Hirsch, Z. Chen, H. Jiao, "Spherical Aromaticity in Ih Symmetrical Fullerenes: The 2(N+1) 2<br />
Rule", Angew. Chem. Int. Ed. 39, 3915 (2000).<br />
[3] M. P. Johansson, J. Jusélius, D. Sundholm, "Sphere Currents <strong>of</strong> Buckminsterfullerene", Angew.<br />
Chem. (in press).<br />
[4] M. P. Johansson, D. Sundholm, J. Vaara, "Au32: A 24-Carat Golden Fullerene", Angew. Chem. Int.<br />
Ed. 43, 2678 (2004).
Chemistry<br />
43
Gold cluster molecular surface chemistry<br />
André Fielicke 1 , Gert von Helden 1 , Gerard Meijer 1 , David B. Pedersen 2 , Benoit Simard 2 and<br />
David M. Rayner 2<br />
B - 7<br />
1 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany<br />
2 Steacie Institute for Molecular Sciences, National Research Council, 100 Sussex Drive, Ottawa, Ontario<br />
K1A 0R6, Canada<br />
The chemistry <strong>of</strong> gold nanoparticles is an important example <strong>of</strong> the fundamental difference<br />
between material in its bulk and in its cluster forms. Whereas bulk gold is chemically inert,<br />
deposited gold nanoparticles and clusters have a highly size-specific catalytic activity. A<br />
dramatic size-dependence in reactivity and catalytic turnover has even been found for isolated<br />
gold clusters containing only a few atoms.<br />
We are working to characterize prototypical reactions on free metal clusters in the gas phase.<br />
The intention is to provide a basis for understanding the chemistry <strong>of</strong> supported nanoparticles.<br />
Our approach is to monitor the independent adsorption, co-adsorption and reaction <strong>of</strong> relevant<br />
reaction partner molecules on size-selected clusters using infrared multi-photon depletion<br />
spectroscopy with a free electron laser. Our ultimate goal is to obtain thermodynamic<br />
information on cluster surface reactions through variable temperature studies.<br />
Here we discuss progress towards this goal, concentrating on gold clusters. We report on the<br />
interaction <strong>of</strong> carbon monoxide, CO, and nitric oxide, NO, with cationic and anionic gold<br />
clusters. Successive adsorption <strong>of</strong> CO molecules on the Aun+ clusters proceeds until a cluster<br />
size specific saturation coverage is reached. Structural information for the bare gold clusters is<br />
obtained by comparing the saturation composition with the number <strong>of</strong> available equivalent sites<br />
presented by candidate structures <strong>of</strong> Aun+. Our findings are in agreement with the planar<br />
structures <strong>of</strong> the Aun + cluster cations with n < �7 suggested by ion mobility experiments<br />
combined with DFT calculations [1]. By inference we also establish the structure <strong>of</strong> the<br />
saturated Aun(CO)m + complexes. In certain cases we find evidence that successive adsorption <strong>of</strong><br />
CO can distort the metal cluster framework. The vibrational spectra <strong>of</strong> the Aun(CO)m+<br />
complexes in both the CO stretching region and in the region <strong>of</strong> the Au-C stretch and the Au-C-<br />
O bend add further support to aid in the Aun+ structure determination, provide information on<br />
the structure <strong>of</strong> the CO complexes and allow comparison with CO adsorbates on deposited<br />
clusters or surfaces.<br />
For Aun- anions we find the same CO uptake patterns reported previously [2]. There is no clear<br />
correlation with geometric structure. Vibrational spectroscopy in the CO stretching region<br />
confirms molecular adsorption <strong>of</strong> CO, discounting the proposal that CO molecules might react<br />
together to form “glyoxylates” on the surface <strong>of</strong> Aun - [2].<br />
Nitric oxide absorption on Aun + shows similar uptake patterns to CO for small clusters, but NO<br />
absorbs less readily on clusters with n > 8. Vibrational spectroscopy shows that NO absorbs<br />
molecularly on Aun+ at 300 K. Aun+ is the first cluster system on which we have been able to<br />
find this direct evidence for molecular absorption <strong>of</strong> NO. The NO stretching frequency, ν(NO),<br />
is consistent with atop NO bonding in a bent configuration but shows a pronounced odd-even<br />
shift that we reproduce by DFT calculations. Finally, preliminary experiments on co-adsorbed<br />
CO and NO show that there is no reaction between CO and NO on Aun + clusters at 300 K.<br />
References<br />
[1] S. Gilb, P. Weis, F. Furche, R. Ahlrichs and M.M. Kappes, J. Chem. Phys. 116, 4094 (2001).<br />
[2] W.T. Wallace and R.L.Whetten, J. Phys. Chem. B 104, 10964 (2000).<br />
45
46<br />
B - 8<br />
Triplatinum carbonyl complexes: preference for terminal sites and<br />
chiral structures<br />
Timo Santa-Nokki and Hannu Häkkinen<br />
Department <strong>of</strong> Physics, Nanoscience Center, University <strong>of</strong> Jyväskylä, Finland<br />
We present a systematic density functional theory (DFT) study on the structures <strong>of</strong><br />
triplatinum carbonyls Pt3(CO)x q with x=1-6 and q=0,-1. The calculations are able to fully<br />
reproduce and explain the experimentally observed anomalous behaviour in the binding energy<br />
<strong>of</strong> the ligands in anionic cluster carbonyls by Grushow and Ervin, 1 with the three first ligands<br />
strongly bound (by 220-275 kJ/mol per ligand), the fourth and fifth ligand weakly bound (by<br />
135 kJ/mol), and the sixth ligand again stronger bound (by about 200 kJ/mol). The first three<br />
ligands bind in a tilted configuration at terminal sites in the plane <strong>of</strong> the triangular platinum<br />
core, making the half-saturated Pt3(CO)3 - a chiral complex. We discuss the relative preference <strong>of</strong><br />
terminal and bridge adsorption sites for CO in Pd, Pt, and Au cluster carbonyls in terms <strong>of</strong> the<br />
strength <strong>of</strong> the relativistic effects in the metal-carbon bond. We also discuss the implications <strong>of</strong><br />
the current work regarding design <strong>of</strong> bimetallic Au-Pt cluster nanocatalysts for CO oxidation. 2<br />
Figure 1. Sequential binding energy <strong>of</strong> CO ligands to anionic platinum cluster carbonyls Pt 3(CO) x - for x=1-6. The<br />
DFT results <strong>of</strong> this work are compared to TCID and PD data from Ref. 1. A conservative estimate for the accuracy <strong>of</strong><br />
the theoretical values is ±10 kJ/mol. For each x we also show the ground state structure <strong>of</strong> the anionic cluster<br />
carbonyl.<br />
References<br />
[1] A. Grushow and K.M. Ervin, J. Am. Chem. Soc. 117, 11612 (1995); A. Grushow and K.M. Ervin,<br />
J. Chem. Phys. 106, 9580 (1997); K.M. Ervin, Int. Reviews in Physical Chemistry 20, 127 (2001).<br />
[2] T. Santa-Nokki and H. Häkkinen, submitted.
Who probes whom: Early transition metal cluster ions meet<br />
(non)aromatic hydrocarbon molecules<br />
Britta Pfeffer, Stephanie Wies, Anita Lagutschenkov, Jens Brück, Matthias Vetter, Tobias Pankewitz,<br />
Gereon Niedner-Schatteburg<br />
TU Kaiserslautern, Fachbereich Chemie, Erwin-Schrödinger-Str. 52, 67663 Kaiserslautern, Germany<br />
B - 9<br />
As already known form former studies [1-4] benzene as well as common olefines react with<br />
niobium cluster cations through complete dehydrogenation. In contrast to other cluster sizes the<br />
Nb19 + cluster is the only one which exclusively binds the aromatic hydrocarbon molecule by<br />
intact adsorption. This exception can also be observed in the reaction with naphthalene (also a<br />
homoaromatic molecule).<br />
In the present work we focus on the difference in reactivity <strong>of</strong> homoaromatic and <strong>of</strong><br />
heteroaromatic systems (benzene, quinoline, naphthaline, pyridine, furan and thiophene).<br />
The data allow for tentative conclusions on the prevailing coordination geometries (parallel or<br />
perpendicular to “cluster suface”). The correspondence <strong>of</strong> cluster to bulk surfaces will be<br />
discussed.<br />
References<br />
[1] J. Chem. Phys. 102 (12), 4870-4884 (1995).<br />
[2] .J. Phys. Chem. 99 (42), 15497-15501 (1995).<br />
[3] J. Chem. Phys. 108 (13), 5398-5403 (1998).<br />
[4] J. Chem. Phys. 262 (1), 143-149 (2000).<br />
47
B - 10<br />
48<br />
Structural and Electronic Properties <strong>of</strong> (HAlO)n Clusters<br />
Yi Dong and Michael Springborg<br />
Physical and Theoretical Chemistry, University <strong>of</strong> Saarland, 66123 Saarbrücken, Germany<br />
The structure <strong>of</strong> (HAlO)n clusters was optimized for n up to 26 using our own 'Aufbau'<br />
approach and for n up to 18 using a genetic-algorithms approach together with a parameterized<br />
density-functional method. The two set <strong>of</strong> results for (HAlO)n from the 'Aufbau' and the geneticalgorithms<br />
approaches are very close, proving that our two unbiased approaches are reliable.<br />
The shape <strong>of</strong> the clusters as well as so-called similarity functions, stability functions are<br />
presented in order to analysing the structural properites <strong>of</strong> the (HAlO)n clusters. Subsequently,<br />
we also study the properties <strong>of</strong> two interacting clusters that were optimized by the 'Aufbau'<br />
approaches in order to study the marcroscopic, nanoscaled HAlO material that is produced in<br />
experiment.
Efficient Low-Temperature Oxidation <strong>of</strong> Carbon-Cluster Anions by<br />
SO2: Atmospheric Soot and Health Implications<br />
B - 11<br />
Andrew J. Leavitt 1,2 , Richard B. Wyrwas 2 , William T. Wallace 2+ , Daniel Serrano 1 , Melissa G. Arredondo 2 ,<br />
Farooq A. Khan 1 , and Robert L. Whetten 2*<br />
1 Department <strong>of</strong> Chemistry, State University <strong>of</strong> West Georgia, Carrollton, GA 30118.<br />
2 School <strong>of</strong> Chemistry and Biochemistry, Georgia Institute <strong>of</strong> Technology, Atlanta, GA 30332-0400.<br />
+Current address: Department <strong>of</strong> Chemistry, Texas A&M University, College Station, TX 77842-30012<br />
*Author to whom correspondences should be addressed.<br />
Carbon-cluster anions, CN - , are very active toward SO2 (sticking probability <strong>of</strong> 0.023 ±<br />
0.005 for C27 - at 25 o C), as compared to their inertness toward other common atmospheric gases<br />
and pollutants. In atmospheric-pressure, fast-flow-reactor experiments at ambient temperature,<br />
primary adsorption <strong>of</strong> SO2 by the carbon cluster anions, N = 4 – 60, yields CNSO2 - (αN) or CN-<br />
1S - (βN), with neutral CO2, as also detected in collision-induced dissociation. At higher<br />
temperatures, the reaction <strong>of</strong> SO2 with nascent carbon clusters yields the αN, βN, and CN-1SO -<br />
(γN) along with undetected CO2 and CO. The size-dependent initial reactivity reflects the<br />
previously established cluster structural transitions, i.e. from linear-chain to cyclic to cage<br />
structures. Secondary adsorption is also observed, with higher intrinsic reactivity, suggesting an<br />
accelerating oxidation process. Such carbon clusters serve as model compounds for blackcarbon<br />
soot, as they are formed in sooting flames and can act as nuclei for the formation <strong>of</strong><br />
primary soot particles, which also share the local structural features <strong>of</strong> active soot particle sites.<br />
These findings may therefore have implications for understanding the health and environmental<br />
effects attributed to the coincidence <strong>of</strong> soot and SO2.<br />
49
B - 12<br />
50<br />
Size Dependent Carbon Monoxide Adsorption on<br />
Neutral Gold Clusters<br />
Nele Veldeman 1 , Peter Lievens 1 , Mats Andersson 2<br />
1 Laboratorium voor Vaste-St<strong>of</strong>fysica en Magnetisme, K.U.Leuven,<br />
Celestijnenlaan 200D, B-3001 Leuven, Belgium<br />
2 Department <strong>of</strong> Experimental Physics, Chalmers University <strong>of</strong> Technology and<br />
Göteborg University, SE-412 96 Göteborg, Sweden<br />
In spite <strong>of</strong> gold being chemically inert as bulk material, supported nanosize gold clusters are<br />
found to show a remarkable catalytic activity for many reactions. Among these are CO<br />
combustion, NOx reduction, methanol synthesis and water-gas shift [1]. In order to clarify the<br />
catalytic behaviour shown by small gold particles supported on metal oxides, a number <strong>of</strong><br />
studies on deposited clusters, mainly focussing on the size and support dependence, have been<br />
performed [2,3]. Although the substrate <strong>of</strong>ten plays an important role, also the investigation <strong>of</strong><br />
chemical reactivity and catalytic activity <strong>of</strong> gas phase clusters is <strong>of</strong> great importance, as they<br />
may provide deeper insight in mechanisms <strong>of</strong> reaction processes. In this respect attention so far<br />
is especially drawn to reactivity and catalytic activity [4,5,6,7,8] <strong>of</strong> ionic gas phase gold<br />
clusters. As a complete understanding <strong>of</strong> the mechanisms involved in heterogeneous catalysis<br />
by nanoscale gold particles still remains a challenge, extended knowledge gained by reactivity<br />
experiments on neutral gas phase gold clusters towards reactants <strong>of</strong> interest could be very<br />
helpful.<br />
We report on experiments probing the reactivity <strong>of</strong> neutral Aun clusters, n=10-65, with CO gas.<br />
The gold clusters are produced in a pulsed laser vaporization cluster source [9], operated at<br />
room temperature (RT) or at liquid-nitrogen temperature (LNT), pass through a low-pressure<br />
reaction cell containing CO gas, and are subsequently laser ionised. The reaction probabilities<br />
are determined by recording mass abundance spectra with time <strong>of</strong> flight mass spectrometry.<br />
The main observations can be summarized as follows. (i) Upon cooling <strong>of</strong> the cluster source to<br />
LNT, the reactivity increases substantially. At LNT, the reaction probabilities for Aun with the<br />
first CO molecule are about a factor ten higher than at RT. Moreover, adsorption <strong>of</strong> two, three<br />
and even four CO molecules is observed, in contrast to RT clusters which at most adsorb one<br />
CO molecule. (ii) The reactivity is found to exhibit strong variations with cluster size, similar at<br />
both temperatures. The observed reaction probabilities yield evidence for electronic properties<br />
governing the size dependence: counting the number <strong>of</strong> delocalised electrons in reacted species<br />
reveals a correlation between reactivity and cluster electronic shell closings, and odd-even<br />
staggering in the reaction probabilities as a function <strong>of</strong> the number <strong>of</strong> atoms is observed.<br />
References<br />
[1] G.C. Bond and D.T. Thompson, Catal. Rev.-Sci. Eng. 41, 319 (1999)<br />
[2] M. Haruta, Catal. Today 36, 153 (1997)<br />
[3] A. Sanchez et al., J. Phys. Chem. A 103, 9573 (1999)<br />
[4] H. Häkkinen and U. Landman, J. Am. Chem. Soc. 123, 9704 (2001)<br />
[5] W.T. Wallace and R.L. Whetten, J. Am. Chem. Soc. 124, 7499 (2002)<br />
[6] J. Hagen et al., Phys. Chem. Chem. Phys. 4, 1707 (2002)<br />
[7] I. Balteanu et al., Phys. Chem. Chem. Phys. 5, 1213 (2003)<br />
[8] D. Stolcic et al. J. Am. Chem. Soc. 125, 2848 (2003)<br />
[9] M. Andersson et al., J. Phys. Chem. 100, 12222 (1996)
B - 13<br />
Photoelectron spectra <strong>of</strong> lanthanum oxide clusters: decreasing electron<br />
affinities with increasing number <strong>of</strong> oxygen atoms<br />
R. Klingeler 1 , G. Lüttgens 1 , P. S. Bechthold 1 , N. Pontius 2 , M. Neeb 2 , W. Eberhardt 2<br />
1 Institut fürFestkörperforschung, Forschungszentrum Jülich, 52425 Jülich, Germany<br />
2 Bessy GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany<br />
We present a systematic investigation <strong>of</strong> the electronic structure <strong>of</strong> La2On (n=1-6) and<br />
La3Om (m=0-4) using photoelectron spectroscopy <strong>of</strong> anions (hν = 3.495 eV). For La2O and<br />
La2O2 the experiments are supported by density functional and configuration interaction<br />
calculations. The results for the C2v and the D2h ground state isomers, respectively, are in good<br />
agreement with the experimental data. In contrast to some other metal dimers and trimers we<br />
find as a general trend a decreasing electron affinity with an increasing number <strong>of</strong> chemisorbed<br />
oxygen atoms.<br />
References<br />
[1] R. Klingeler, G. Lüttgens, N. Pontius, R. Rochow, P.S. Bechthold, M. Neeb, and W. Eberhardt,<br />
Eur. Phys. J. D 9, 263 (1999).<br />
51
B - 14<br />
52<br />
Binding energies <strong>of</strong> CO and H2O on gold cluster cations<br />
Aun+ (n=1-65): A FT-ICR kinetics study<br />
Marco Neumaier 1 , Florian Weigend 1 , Oliver Hampe 1 , and Manfred M. Kappes 1,2<br />
1 Institut für Nanotechnologie, Forschungszentrum Karlsruhe, D-76021 Karlsruhe, Germany<br />
2 Institut für Physikalische Chemie, <strong>Universität</strong> Karlsruhe, D-76128 Karlsruhe, Germany<br />
Room temperature CO adsorption on isolated gold cluster cations is studied over a wide size<br />
range (Aun + , 1
The Bonding <strong>of</strong> CO with Au8: Evidence <strong>of</strong> Cluster Charging<br />
M. A. Röttgen 1 , A. S. Wörz 1 , K. Judai 1,3 , S. Abbet 1 , J. M. Antonietti 1 , U. Heiz 1 , B. Yoon 2 , and<br />
U. Landman 2<br />
1 Institute <strong>of</strong> Surface Chemistry and Catalysis, <strong>Universität</strong> Ulm, 89069 Ulm, Germany<br />
2 Georgia Institute <strong>of</strong> Technology, School <strong>of</strong> Physics, Atlanta, Georgia 30332-0430, USA<br />
3 Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan<br />
B - 15<br />
While Gold is inert as bulk material, it becomes catalytically active as nanoscale particles or<br />
clusters supported onto oxide support materials. In the last few years, effort was made to get a<br />
better insight into the relevant reaction mechanisms and to understand this astonishing<br />
phenomenon on a molecular level. For large gold particles a few nanometers in size, it is<br />
discussed on the one hand whether the catalytic activity can be explained by the presence <strong>of</strong><br />
active sites on the cluster-support interface or by low-coordinated, highly reactive sites. On the<br />
other hand, for small clusters, the gold octamers bound to F-centers <strong>of</strong> an MgO surface are the<br />
smallest known gold heterogeneous catalysts able to transform CO into CO2. The key for the<br />
low-temperature conversion on Au8 is the binding <strong>of</strong> the molecular oxygen and the concomitant<br />
O-O bond activation to a peroxo-like adsorbate state. This is possible as the cluster’s electronic<br />
states show resonance with the 2π* molecular states <strong>of</strong> oxygen and as these antibonding states<br />
are pushed below the Fermi level <strong>of</strong> the system upon interaction with the cluster. Interestingly,<br />
the same cluster bound to a terrace site <strong>of</strong> an MgO surface is inert for the combustion reaction.<br />
Extensive ab initio calculations predicted that charging from the F-center into the cluster is<br />
essential for the activation <strong>of</strong> gold octamers.<br />
In this contribution, we present new findings showing experimental evidence for this prediction.<br />
The measured CO stretch frequencies, ν(CO), under reaction conditions are red-shifted by about<br />
30-50 cm-1 for the octamer bound to the F-center (Au8/CO/O2/MgO(FC)) in comparison to the<br />
octamer bound to the five-coordinated terrace sites (Au8/CO/O2/MgO(O5c)). Extensive ab<br />
initio calculations reveal that this shift is caused by enhanced backdonation into the antibonding<br />
2π* orbital <strong>of</strong> CO adsorbed on the Au8/O2/MgO(FC) complex and reveal important details <strong>of</strong><br />
the bonding <strong>of</strong> CO for understanding the backdonation. In addition, calculations on free<br />
Au8/O2/CO complexes indeed show this effect to be related to a substantial change in charging<br />
<strong>of</strong> the cluster [1].<br />
References<br />
[1] B. Yoon et al., Accepted for Publication in Science (2004).<br />
53
B - 16<br />
54<br />
Reactivity <strong>of</strong> Size-Selected Gas-Phase Transition Metal Carbide and<br />
Sulfide Clusters<br />
James Lightstone 1 , Melissa Patterson 1 , Robert J. Beuhler 2 1, 2<br />
, Michael G. White<br />
1 Department <strong>of</strong> Chemistry, Stony Brook University, Stony Brook, NY 11974, USA<br />
2 Chemistry Department, Brookhaven National Laboratory, Upton, NY 11973, USA<br />
We have recently constructed a cluster deposition apparatus which employs a magnetron<br />
sputtering source for generating gas-phase cation clusters <strong>of</strong> pure metals and metallic<br />
compounds. The focus is on generating clusters <strong>of</strong> the early transition metal compounds<br />
(carbide and sulfides), which are known in their bulk form to be active catalysts for a wide<br />
range <strong>of</strong> heterogeneous reactions [1,2]. In many cases, metal carbides <strong>of</strong>fer distinct advantages<br />
over the parent metal in selectivity and resistance to poisoning, and for certain reactions their<br />
catalytic behavior is similar to that <strong>of</strong> the Group 8-10 noble metals [2,3]. Very recent theoretical<br />
calculations also suggest that small carbide clusters, i.e., the Ti8C12 Met-Car and Ti14C13<br />
nanocrystallite, are more reactive than bulk TiC surfaces [4]. The work reported here examines<br />
the gas-phase reactivity <strong>of</strong> small transition metal carbide and sulfide clusters as a first step<br />
towards investigations <strong>of</strong> model catalysts prepared by size-selected deposition.<br />
Ion beams containing a wide array <strong>of</strong> transition metal compound clusters, TxMy + (T ≡ Ti,<br />
Mo, Zr, Nb; M ≡ C, S), were generated using a magnetron sputtering source, including “magic”<br />
number species such as the Ti8C12 + Met-Car. The gas-phase reactivity <strong>of</strong> mass-selected TxMy +<br />
clusters was studied using a hexapole collision cell, into which reactive gases were introduced,<br />
and a second quadrupole mass filter for product detection. Results will be presented for the<br />
adduct formation and reactions <strong>of</strong> the Ti8C12 + Met-Car with a variety <strong>of</strong> sulfur containing<br />
molecules, such as OCS shown in the accompanying figure below. In addition, we will also<br />
present results on the reactivity <strong>of</strong> MoxSy + clusters and future plans for size-selected cluster<br />
deposition. This work was supported by the U.S. Department <strong>of</strong> Energy, Office <strong>of</strong> Basic Energy<br />
Sciences, Division <strong>of</strong> Chemical Sciences under contract No. DE-AC02--98CH10886<br />
Figure 1. Mass spectrum <strong>of</strong> the reaction<br />
products resulting from collisions between<br />
Ti8C 12 + and OCS at 300K. .<br />
References<br />
500 600 700 800 900 1000<br />
[1] J.G. Speight, The Chemistry and Technology <strong>of</strong> Petroleum, second ed., New York, McGraw-Hill,<br />
1991.<br />
[2] Chen, J. G., Chem. Rev. 1996, 96, 1477; Oyama, S. T., Catal. Today 15, 179 (1992).<br />
[3] Levy, R. L.; Boudart, M., Science 181, 547 (1973).<br />
[4] H. Hou, J. T. Muckerman, P. Liu and J. A. Rodriguez, J. Phys. Chem. 107, 9344 (2003); P. Liu and<br />
J. A. Rodriguez, J. Chem. Phys. 119, 10895 (2003).<br />
Intensity<br />
1.20E-008<br />
1.00E-008<br />
8.00E-009<br />
6.00E-009<br />
4.00E-009<br />
2.00E-009<br />
0.00E+000<br />
Ti 8 C 12<br />
Ti 8 C 12 + S<br />
Ti 8 C 12 + SCO<br />
Ti 8 C 12 + S(SCO) 3<br />
Mass<br />
Ti 8 C 12 + S(SCO) 5
B - 17<br />
Probing Strong Hydrogen Bonds and Cold Metal Oxide Clusters with<br />
Infrared Photodissociation Spectroscopy<br />
Knut R. Asmis<br />
Abteilung Molekülphysik, Fritz-Haber-Institut der Max-Planck-Gesellschaft<br />
Faradayweg 4-6, D 14195 Berlin<br />
In recent years much effort has been aimed at improving the sensitivity and selectivity <strong>of</strong><br />
experimental methods to study the vibrational spectroscopy <strong>of</strong> gas phase ions. Due to the lack <strong>of</strong><br />
widely tunable infrared (IR) light sources most <strong>of</strong> these studies had been limited to the region<br />
above 2400 cm -1 , i.e., the spectral region <strong>of</strong> hydrogen-stretching motions and <strong>of</strong> IR-active<br />
combination bands. The application <strong>of</strong> the infrared free-electron laser FELIX, which generates<br />
tunable radiation in the 40 – 2200 cm -1 region, to molecular spectroscopy by Meijer, von Helden<br />
and coworkers has bridged this gap [1]. We have recently extended their technique to study the<br />
vibrational spectroscopy <strong>of</strong> mass-selected gas-phase cluster cations and anions at variable<br />
temperature. Application <strong>of</strong> this technique to two important compound classes will be discussed<br />
and compared to the results <strong>of</strong> complimentary experiments on mass-selected neutral clusters<br />
using femtosecond pump-probe spectroscopy.<br />
The hydrogen bond interaction is key to understanding the structure and properties <strong>of</strong> water<br />
and biomolecules. However, our understanding <strong>of</strong> strong, low-barrier hydrogen bonds and their<br />
central role in enzyme catalysis, biomolecular recognition, proton transfer across biomembranes<br />
and proton transport in aqueous media remains sketchy. We recently measured the first IR<br />
spectra <strong>of</strong> several prototypical systems, directly probing the shared proton region <strong>of</strong> the<br />
potential energy surface [2,3]. Our experiments demonstrate that the theoretical description <strong>of</strong><br />
the vibrations <strong>of</strong> strong hydrogen bonds is considerably more complex than originally<br />
anticipated and not yet solved satisfactorily, even for small systems and at the highest levels <strong>of</strong><br />
theory currently available.<br />
Transition metal oxides play an increasingly important role in heterogeneous catalysis.<br />
Recent gas-phase reactivity studies on vanadium oxide cluster ions were aimed at understanding<br />
the nature <strong>of</strong> the reactive sites. The interpretation <strong>of</strong> the reactivity data requires information on<br />
the structure <strong>of</strong> the cluster ions. We employ IR photodissociation spectroscopy in combination<br />
with electronic structure calculations to identify the geometric structure as well as structural<br />
trends as a function <strong>of</strong> cluster size in vanadium oxide cluster cations and anions [4]. For the<br />
cluster anions we present the first experimental evidence for the formation <strong>of</strong> polyhedral<br />
vanadium oxide cages in the gas phase. The measured IR spectra are sensitive probes for charge<br />
localization <strong>of</strong> unpaired d-electrons and show a strong resemblance with the IR spectrum <strong>of</strong> a<br />
V2O5 surface already at medium cluster sizes.<br />
References<br />
[1] G. von Helden, I. Holleman, G. M. H. Knippels, A. F. G. van der Meer, and G. Meijer, Phys. Rev.<br />
Lett. 79, 5234 (1997).<br />
[2] K. R. Asmis, N. L. Pivonka, G. Santambrogio, M. Brümmer, C. Kaposta, D. M. Neumark, and L.<br />
Wöste, Science 299, 1375 (2003).<br />
[3] M. Nee, C. Kaposta, A. Osterwalder, C. Cibrian Uhalte, T. Xie, A. Kaledin, S. Carter, J. M.<br />
Bowman, G. Meijer, D. M. Neumark, and K. R. Asmis, J. Chem. Phys. 121, 7259 (2004).<br />
[4] K. R. Asmis, G. Meijer, M. Brümmer, C. Kaposta, G. Santambrogio, L. Wöste, and J. Sauer, J.<br />
Chem. Phys. 120, 6461 (2004).<br />
55
B - 18<br />
56<br />
Oxygen adsorption at anionic free and supported Au clusters<br />
L. M. Molina 1,2 and B. Hammer 1<br />
1 iNANO and Department <strong>of</strong> Physics and Astronomy, University <strong>of</strong> Aarhus, DK-8000 Aarhus C, Denmark<br />
2 Departamento de Física Teórica, Universidad de Valladolid, E-47011 Valladolid, Spain<br />
Recently, much attention has been paid to the catalytic activity <strong>of</strong> supported Au<br />
nanoparticles and clusters [1]. Both small free unsupported anions [2] and MgO-supported<br />
clusters [3] have been found very active towards CO oxidation. However, sizable differences in<br />
the size-dependent activity are found on each case, which are difficult to explain. In this work,<br />
the structure, stability and O2 adsorption properties <strong>of</strong> free anionic Aun - (n=1-11) clusters and<br />
negatively charged Aun clusters supported at defected MgO(100) surfaces are investigated using<br />
density functional theory. The free anionic clusters with an even number <strong>of</strong> atoms readily<br />
adsorb O2 since the excess unpaired electron can be easily transferred to the adsorbate. On the<br />
contrary, Au clusters supported at F + -centers show a much more complex behaviour. They attain<br />
similar electronic structure as the anionic free clusters, but the Madelung potential pins one<br />
electronic orbital to the defect. For large band gap clusters (mainly small clusters, which prefer<br />
2D geometries, see Figure) this is the orbital with the excess electron, which therefore cannot be<br />
transferred to an adsorbate, meaning that O2 adsorbs only weakly. Larger clusters become threedimensional<br />
and more metalic and hence capable <strong>of</strong> screening the support potential and binding<br />
O2 with charge transfer. This helps to understand why the supported clusters only become active<br />
starting at Au8 [3], whereas free Au6 - has been found to be extremely active [2].<br />
Figure 1. Equilibrium structures for O 2 adsorption at Au n (n=2-11) clusters attached to an F + -center. For n=4-11, the<br />
most representative 2D and 3D Au n isomers are shown. At Au 7-Au 8, a transition from 2D to 3D is found.<br />
References<br />
[1] M. Haruta, Catal. Today 36, 153 (1997).<br />
[2] W. T. Wallace and R. L. Whetten, J. Am. Chem. Soc. 124, 7499 (2002).<br />
[3] A. Sanchez et al., J. Phys. Chem A 103, 9573 (1999).
B - 19<br />
Density Functional Studies Of Noble Metal Clusters. Adsorption Of O2<br />
And CO On Gold And Silver Clusters<br />
Eva M. Fernández 1 , María B. Torres 2 , and Luis C. Balbás 1<br />
1 Dpto. de Física Teórica, Atómica y Óptica, Universidad de Valladolid E-4701 Valladolid, Spain<br />
2 Dpto. de Matemáticas y Computación, Universidad de Burgos E-090006 Burgos, Spain<br />
By means <strong>of</strong> first-principles density functional calculations, based on norm-conserving<br />
pseudo-potentials and numerical atomic basis sets, we study different noble metal cluster<br />
systems and properties. First, we show that, together with relativistic effects, the type <strong>of</strong><br />
exchange-correlation functional (GGA or LDA) is more critic for Au than for Ag or Cu clusters<br />
in order to determine the planar or three dimensional cluster geometry 1 . Second, we find cagelike<br />
stable structures for neutral Au18, Au20, Au32, Au50, and Au162, see fig.1. However, after<br />
adding an extra electron only Au20 - remains cage-like. On the other hand, Ag20 and Cu20 clusters<br />
adopt compact amorphous-like Cs structures. Third, we investigate the element- and sizedependent<br />
electron stability <strong>of</strong> gold clusters cations doped with a transition metal impurity 2 ,<br />
AunTM + (TM = Sc, Ti, V, Cr, Mn, Fe, Au; n ≤ 9), and we obtain a clear explanation <strong>of</strong> the<br />
cluster abundance peaks observed recently in photo-fragmentation experiments. Fourth, we<br />
study the size dependent adsorption <strong>of</strong> Om (m=2,4) molecules on small Agn - anion clusters (3≤ n<br />
≤9), as well as the adsorption <strong>of</strong> O2 on neutral Aun (5 ≤ n ≤ 10) and anions Aun - (n ≤ 7) clusters.<br />
The adsorption energy <strong>of</strong> O2 show marked odd even effects in all the cases. For Agn - anions<br />
with odd (even) n, the adsorption <strong>of</strong> a second O2 molecule increase (decrease) the adsorption<br />
energy <strong>of</strong> O2. The atomic O on Aun - O is preferable for n ≥ 4 than O2 adsorption. The<br />
dissociative adsorption is spontaneous for neutral gold clusters with n=6,7. For Aun, clusters<br />
with odd number <strong>of</strong> atoms are more active toward O2 adsorption. The O2 adsorbs preferably on<br />
top <strong>of</strong> Au atoms, except for Au5, for which a bridge site is favorable, see fig. 2. Fifth, we study<br />
also the size dependent adsorption <strong>of</strong> CO on small Aun clusters (5 ≤ n ≤ 10). The binding energy<br />
<strong>of</strong> CO adsorption on Au does not present odd even effects with clusters size. Top position is<br />
preferable for CO adsorption except for n = 5,7. Cluster with n = 5,7 present the biggest binding<br />
energy.<br />
We study also the trend in the bond distances, the vibrational frequencies and Mulliken<br />
population <strong>of</strong> adsorbed species on gold clusters.<br />
Figure 1. Cage-like and isomeric compact structures for Aun with n = 18, 20, 32, 50 and 162.<br />
Figure 2. O2 adsorption on Aun clusters. * dissociative adsorption. + molecular adsorption.<br />
References<br />
[1] E. M. Fernández, J. M. Soler, I. L. Garzón and L. C. Balbás, Phys. Rev. B 70, 165403 (2004).<br />
[2] M. B. Torres, E. M. Fernández and L. C. Balbás, Phys. Rev. B (submitted).<br />
57
B - 20<br />
Gold Clusters, CO-Chemisorbed Au Clusters, and Binary Au Clusters<br />
58<br />
Xi Li, B. Kiran, H. J. Zhai, Jun Li, Hai-Feng Zhang, and Lai-Sheng Wang<br />
Department <strong>of</strong> Physics, Washington State University, 2710 University Drive, Richland, WA 99352, USA<br />
and W. R. Wiley Environmental Molecular Sciences Laboratory and Chemical Science Division, Pacific<br />
Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA.<br />
Gold is a unique element with unusual chemistry due to the strong relativistic effect [1]. We<br />
will present our recent work on small gold clusters [2-4], CO-chemisorbed gold clusters [5], and<br />
novel gold-containing molecules [6-8]. We found previously that Au20 is a highly stable<br />
tetrahedral cluster [2]. Recently, we showed that we can also synthesize the tetrahedral Au20<br />
cluster in solution with phosphine ligands [4]. In experiments aimed at providing insight into the<br />
catalytic effect <strong>of</strong> nanogold, we studied CO-chemisorbed Au clusters, Aum(CO)n - (m = 2-5; n =<br />
1-7) [5]. The photoelectron data suggest that CO acts as an electron donor to the Au clusters and<br />
provide information about the CO-chemisorption site. This work provides direct experimental<br />
insight into the cooperative chemisorption <strong>of</strong> CO and O2 onto Au clusters.<br />
Au13 does not have the high symmetry Ih structure [3]. However, a class <strong>of</strong> stable Ih clusters<br />
containing 12 Au atoms and an impurity atom (M), M@Au12, was predicted to have Ih structures<br />
[9]. We will report our experimental observation and theoretical confirmation <strong>of</strong> these highly<br />
stable and symmetric gold clusters with M = Mo, W, V, Na, and Ta [6,7]. Finally we will<br />
present our discovery <strong>of</strong> the novel H-like chemistry <strong>of</strong> Au in forming the highly stable<br />
aurosilane SiAu4 and other Si-Au clusters in analogy to Si-hydride molecules [8].<br />
References<br />
Td Au20 Au20(PH3)4 Ih M@Au12 Td SiAu4<br />
[1] P. Pyykko, Angew. Chem. Int. Ed. 43, 4412 (2004).<br />
[2] J. Li, X. Li, H. J. Zhai, and L. S. Wang, Science 299, 864-867 (2003).<br />
[3] H. Häkkinen, B. Yoon, U. Landman, X. Li, H. J. Zhai, and L. S. Wang, J. Phys. Chem. A 107,<br />
6168-6175 (2003).<br />
[4] H. F. Zhang, M. Stender, R. Zhang, C. M. Wang, J. Li, and L. S. Wang, J. Phys. Chem. B 108,<br />
12259-12263 (2004).<br />
[5] H. J. Zhai and L. S. Wang, J. Chem. Phys., in press.<br />
[6] X. Li, K. Boggavarapu, J. Li, H. J. Zhai, and L. S. Wang, Angew. Chem. Int. Ed. 41, 4786-4789<br />
(2002).<br />
[7] H. J. Zhai, J. Li, and L. S. Wang, J. Chem. Phys. 121, 8369-8374 (2004).<br />
[8] B. Kiran, X. Li, H. J. Zhai, L. F. Cui, and L. S. Wang, Angew. Chem. Int. Ed. 43, 2125-2129<br />
(2004).<br />
[9] P. Pyykko and N. Runeberg, Angew. Chem. Int. Ed. 41, 2174-2176 (2000).
B - 21<br />
Mass-Selected Infrared Photodissociation Spectroscopy <strong>of</strong> Vanadium<br />
Oxide Cluster Anions<br />
G. Santambrogio 1 , M. Brümmer 1 , S. Fontanella 1 , L. Wöste 1 , J. Sauer 2 , G. Meijer 3 , and K. R. Asmis 3<br />
1 Institut für Experimentalphysik, Freie <strong>Universität</strong> Berlin, Arnimallee 14, Berlin, 14195, Germany<br />
2 Institut für Chemie, Humboldt-<strong>Universität</strong> Berlin, Unter den Linden 6, Berlin, 10099, Germany<br />
3 Abteilung Molekülphysik, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195,<br />
Berlin, Germany<br />
We present infrared spectra for gas phase vanadium oxide cluster anions. Structures are<br />
assigned on the basis <strong>of</strong> comparison between measured spectra and DFT calculations. We<br />
- -<br />
concentrate on the cluster size between V2O6 and V8O20 . Cage structures, which were originally<br />
predicted, [1] have now been spectroscopically identified for the first time. The spectra show<br />
three characteristic absorption regions <strong>of</strong> the IR spectrum which correspond to three different<br />
vibrational modes, namely the peroxo-modes at highest energies around 1100 cm -1 , the vanadylmodes<br />
in the intermediate region from 920 to 1020 cm -1 , and the V-O-V modes below 900 and<br />
to about 600 cm -1 . The smallest clusters studied, the divanadium oxide anions, can be classified<br />
-<br />
as “quasi-planar”, characterized by nearly planar V-O-V-O ring. V3O8 is an intermediate case; it<br />
-<br />
is the first anion that shows a three dimensional backbone structure. V4O10 is the first cage<br />
structure, in which each vanadium atom forms three V-O-V bonds and one vanadyl bond. Cages<br />
-<br />
are observed for all larger clusters up to V8O20 , indicating that these are particular stable<br />
-<br />
structures. The spectrum <strong>of</strong> V4O20 (see figure) reveals some striking similarities with the<br />
properties <strong>of</strong> a vanadium oxide single crystal surface[2] suggesting it is an interesting candidate<br />
for studying surface adsorption and surface reactivity on a model system in the gas phase.<br />
References<br />
Fragment Ion Signal<br />
Intensity<br />
0<br />
0<br />
Photon Energy (cm -1 )<br />
600 700 800 900 1000 1100 1200 1300 1400<br />
V-O(3)<br />
O-V-O<br />
V-O(2)<br />
V=O<br />
V-O(1)<br />
IR-PD (gas phase)<br />
V 8 O 20 ¯→ V 4 O 10 ¯ + V 4 O 10<br />
HREELS (surface)<br />
600 700 800 900 1000 1100 1200 1300 1400<br />
Electron Energy Loss (cm -1 )<br />
[1] S. F. Vyboishchikov and J. Sauer, J. Chem. Phys. A 105, 8588 (2000).<br />
[2] B. Tepper, B. Richter, A.-C. Dupuis, H. Kuhlenbeck, C. Hucho, P. Schilbe, M. A. bin Yarmo, and<br />
H.-J. Freund, Surface Science 496, 64 (2002).<br />
59
B - 22<br />
60<br />
Probing the Electronic Structure and Chemical Bonding <strong>of</strong> Metal<br />
Oxide Clusters Using Photoelectron Spectroscopy<br />
Hua-Jin Zhai, B. Kiran, Xi Li, and Lai-Sheng Wang<br />
Department <strong>of</strong> Physics, Washington State University, 2710 University Drive, Richland, WA 99352, USA<br />
and W. R. Wiley Environmental Molecular Sciences Laboratory and Chemical Science Division, Pacific<br />
Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA<br />
We report investigations <strong>of</strong> the electronic structure and chemical bonding <strong>of</strong> metal oxide<br />
clusters using photoelectron spectroscopy and theoretical calculations. One key advantage <strong>of</strong><br />
cluster studies is the flexibility to create clusters with any stoichiometry. It was shown [1] that<br />
metal oxide clusters with fixed numbers <strong>of</strong> metal atoms exhibit a behavior <strong>of</strong> sequential<br />
oxidation up to the maximum oxidation state <strong>of</strong> the metal atoms. For oxygen-rich clusters, O2<br />
unit begins to appear as per- or super-oxide. In this work, we show our recent investigation <strong>of</strong><br />
Mo and W oxide clusters (MoOx - and WOx - , x = 3-5) [2]. Comparisons between photoelectron<br />
spectra and theoretical calculations are used to provide detailed information about the structures<br />
and chemical bonding <strong>of</strong> the oxide clusters. The MO3 molecules are stoichiometric species and<br />
are observed to be closed shell with large energy gaps. However, we observe that the O2 moiety<br />
does not appear in the O-rich MO4 species, which exhibit a distorted tetrahedral structure with<br />
diradical character because <strong>of</strong> the strong M-O bonding. WO5 is found to be an unusual chargetransfer<br />
complex, (O2 - )WO3 + , also with diradical character.<br />
We will also report recent studies on the electronic structure <strong>of</strong> polyoxometalate anions (PMAs)<br />
using electrospray and photoelectron spectroscopy [3]. PMAs are a class <strong>of</strong> well-defined and<br />
negatively charged nanoclusters that exist in solution. The electrospray technique allows these<br />
species to be studied in the gas phase, facilitating direct comparisons between theory and<br />
experiment.<br />
References<br />
[1] L. S. Wang, H. Wu, and S. R. Desai, Phys. Rev. Lett. 76, 4853-4856 (1996).<br />
[2] H. J. Zhai, B. Kiran, L. F. Cui, X Li, D. A. Dixon, and L. S. Wang, J. Am. Chem. Soc. 126, 16134-<br />
16141 (2004).<br />
[3] X. Yang, T. Waters, X. B. Wang, R. A. J. O’Hair, A. G. Wedd, D. A. Dixon, J. Li, and L. S. Wang,<br />
J. Phys. Chem. A 108, 10089-10093 (2004).
Interaction <strong>of</strong> oxygen with mass-selected Ag cluster anions and<br />
nanoparticles<br />
Ignacio Lopez-Salido, Dong Chan Lim, Gerd Ganteför, and Young Dok Kim<br />
Department <strong>of</strong> Physics, University <strong>of</strong> <strong>Konstanz</strong>, D-78457 <strong>Konstanz</strong>, Germany<br />
http://www.clusterphysik.uni-konstanz.de/<br />
B - 23<br />
Adsorption <strong>of</strong> oxygen on free negatively charged Ag clusters were studied using Time-<strong>of</strong>-<br />
Flight mass spectrometry and photoelectron spectroscopy. In contrast to the results <strong>of</strong> Au cluster<br />
anions, which become inert towards oxygen chemisorption for Au n - with n > 20, Ag clusters<br />
consisting <strong>of</strong> more than 30 atoms are still reactive towards O 2 chemisorption. The even-odd<br />
alteration <strong>of</strong> the O 2 chemisorption reactivity was found, which has been also observed for the<br />
Au cluster anions. Photoelectron spectroscopy was used to study the nature <strong>of</strong> oxygen species<br />
on the Ag cluster anions. To shed light on the chemical properties <strong>of</strong> larger Ag nanoparticles,<br />
we deposited Ag on Highly Ordered Pyrolytic Graphite (HOPG) surfaces, leading to the<br />
formation <strong>of</strong> Ag nanoparticles with particle diameters up to 10 nm. Scanning Tunneling<br />
Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS) results suggest quite narrow<br />
size distributions <strong>of</strong> Ag islands on HOPG, allowing investigations on size dependent changes <strong>of</strong><br />
electronic and chemical properties <strong>of</strong> Ag nanoparticles. For the Ag nanoparticles smaller than<br />
10 nm, completely different oxidation patterns were observed compared to the Ag bulk crystal.<br />
We found Ag oxide species, which cannot be observed by oxidation <strong>of</strong> Ag bulk crystal.<br />
Implication <strong>of</strong> this result in heterogeneous catalysis is discussed in connection with the size<br />
selectivity in ethylene epoxidation.<br />
61
B - 24<br />
62<br />
Joint theoretical and experimental investigations <strong>of</strong> reactivity <strong>of</strong><br />
anionic and cationic gold oxide clusters with carbon monoxide<br />
Christian Bürgel 1 , Roland Mitrić 1 , Vlasta Bonačić-Koutecký 1 , Michele L. Kimble 2 , Nelly A. Moore 2 , A.<br />
Welford Castleman Jr. 2<br />
1 Humboldt <strong>Universität</strong> zu Berlin, Institut für Chemie, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany<br />
2 Department <strong>of</strong> Chemistry and Physics, Pennsylvania State University, University Park, Pennsylvania<br />
16802, USA<br />
Recent literature shows that gold oxides, containing both atomic and molecular oxygen may<br />
play a role as the active site in supported gold catalysts. Therefore, a fundamental question can<br />
be raised as to whether it is sufficient to have an atomic oxygen in order for the oxidation<br />
reaction to proceed. A second fundamental question concerns the role <strong>of</strong> a charge. We will<br />
address both aspects by presenting the oxidation <strong>of</strong> CO in the presence <strong>of</strong> anionic and cationic<br />
gas phase gold oxide clusters. The influence <strong>of</strong> the charge on the association and replacement<br />
reaction has been also investigated. The experimental studies were carried out utilizing a metal<br />
ion flow tube in conjunction with a guided ion beam apparatus where gold oxides with both<br />
atomized and molecular oxygen are produced. Based on DFT and CCSD calculations we<br />
identified the reactive center and proposed reaction mechanisms. It will be shown that a<br />
peripheral O-atom is the most effective center for the oxidation reaction, while cooperative<br />
effects are mandatory for a reaction to proceed if molecular oxygen is involved. However, the<br />
presence <strong>of</strong> atomic oxygen does not guarantee that the oxidation reaction will proceed. We also<br />
wish to show the importance <strong>of</strong> cationic clusters for the association and replacement reactions.<br />
References<br />
[1] M. L. Kimble, A. W. Castleman, Jr., R. Mitrić, C. Bürgel, V. Bonačić-Koutecký, J. Am. Chem.<br />
Soc., 126, 2526 (2004).<br />
[2] M. L. Kimble, C. Bürgel, Nelly A. Moore A. W. Castleman, Jr., R. Mitrić,<br />
V. Bonačić-Koutecký, J. Am. Chem. Soc., in prep.
Dynamics<br />
63
Photoionization Dynamics <strong>of</strong> Pure Helium Droplets<br />
Darcy S. Peterka 1,2 , Jeong Hyun Kim 2 , Chia Wang 1 , Musahid Ahmed 2 , Daniel M. Neumark 1,2<br />
B - 25<br />
1 College <strong>of</strong> Chemistry, University <strong>of</strong> California, Berkeley, Address, Berkeley, 94720, USA<br />
2 Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Rd, Berkeley, Ca<br />
94720, USA<br />
Helium nanodroplets have been demonstrated to provide a unique environment for<br />
spectroscopic studies. Their ability to capture and cool foreign dopants in a controlled way has<br />
led to their description as an "ultracold nanolaboratory". Many groups have used this property to<br />
their advantage, performing rotational and vibrational spectroscopic studies in great detail, with<br />
slightly less work being done by probing electronic transitions. However, there is almost no<br />
work on the photoionization <strong>of</strong> pure clusters. We have studied the single photon vacuum<br />
ultraviolet ionization <strong>of</strong> pure helium droplets below the atomic helium ionization threshold<br />
using velocity-mapped photoelectron imaging. We see wavelength dependant changes in the<br />
ionization dynamics <strong>of</strong> the droplet. Below the atomic threshold, indirect processes are the<br />
dominant source <strong>of</strong> electrons, leading to electrons <strong>of</strong> very low kinetic energy 1 . With photon<br />
energies larger than the Helium atom ionization energy, direct ionization to Hen + takes place,<br />
giving fast photoelectrons.<br />
References<br />
[1] D. S. Peterka, A. Lindinger, L. Poisson, M. Ahmed, and D.M. Neumark, Phys. Rev. Lett. 91,<br />
043401 (2003).<br />
65
B - 26<br />
66<br />
Excited-state relaxation dynamics in Au cluster anions<br />
J. Stanzel, F. Burmeister, M. Neeb, W. Eberhardt<br />
BESSY GmbH, Albert-Einstein-Str. 15, 12489 Berlin<br />
We report on time-resolved two-photon photoemission measurements on small gold cluster<br />
anions (Aun - , n = 6, 7, 8, 9, 14, 20). These measurements were performed to monitor the<br />
relaxation dynamics <strong>of</strong> optically excited states. As reported recently optically excited electronic<br />
states in Au3 - and Au6 - are long lived (> 1 ns) [1] in comparison to open d-shell metal clusters as<br />
Pt, Pd, Ni [2] and W [3]. This is mainly attributed to the large HOMO-LUMO band gap <strong>of</strong> gold<br />
clusters, which minimizes the probability <strong>of</strong> fast electron-electron-scattering. As we will present<br />
here, larger Au-clusters, e.g. Au8 - (fig. 1) can show relaxation processes in the lower picosecond<br />
range.<br />
Figure 1. Time resolved two-photon photoemission spectra <strong>of</strong> Au 8 - : The peak at 2.9 eV binding energy is recorded<br />
with the probe pulse (3.12 eV) and is assigned to the HOMO. In the pump & probe spectra (pump: 1.56 eV) a peak<br />
appears above the HOMO at 1.4 eV with its maximum at a delay <strong>of</strong> 0.1 ps. At longer delay times this peak broadens<br />
and shifts to higher binding energies until it completely vanishes.<br />
References<br />
[1] M. Niemietz, P. Gerhardt, G. Ganteför, Y.D. Kim, Chem. Phys Lett., 380, 99 (2003).<br />
[2] N. Pontius, M. Neeb, W. Eberhardt, G. Lüttgens, P. S. Bechthold, Phys. Rev. B 67, 354251 (2003)<br />
and references therein.<br />
[3] to be published.
Fast Electronic Relaxation in Metal Clusters via Excitation <strong>of</strong><br />
Coherent Shape Deformations: Slipping Through a Bottleneck<br />
V. V. Kresin 1 , Yu. N. Ovchinnikov 2 , V. Z. Kresin 3<br />
1 Dept. <strong>of</strong> Physics, University <strong>of</strong> Southern California, Los Angeles, California 90089-0484, USA<br />
2 Landau Institute for Theoretical Physics, Russian Academy <strong>of</strong> Sciences, Moscow 117332, Russia<br />
3 Lawrence Berkeley Laboratory, University <strong>of</strong> California, Berkeley, California 94720, USA<br />
B - 27<br />
We introduce and analyze a channel <strong>of</strong> electronic relaxation in metallic clusters which<br />
enables large energy transfer to the ionic subsystem and, correspondingly, fast electron<br />
relaxation dynamics. The discreteness <strong>of</strong> electronic levels in finite size-quantized systems such<br />
as metal nanoparticles, quantum dots, etc., represents a challenge for understanding the<br />
relaxation behavior <strong>of</strong> excited electrons. As is known, cases when the spacing between<br />
electronic energy levels exceeds the vibrational frequencies raise the prospect <strong>of</strong> so-called<br />
relaxation bottleneck phenomena. That is to say, if in order to drop to a lower-lying level an<br />
excited electron needs to emit multiple simultaneous vibrational quanta, the probability <strong>of</strong> such<br />
a transition should be strongly suppressed: multiphonon processes normally occur only as high<br />
order interaction corrections.<br />
The proposed relaxation mechanism which overcomes the bottleneck involves the special ability<br />
<strong>of</strong> free clusters to deform. A cluster with an electron in a previously unoccupied orbital (e.g.,<br />
excited by light or externally injected) will proceed to deform from its original shape.<br />
Microscopically, this deformation invalidates the selection rule which in the lowest order allows<br />
only single-phonon processes: whereas the rule assumes that the ionic equilibrium position is<br />
fixed during the electronic transition, a shift in the cluster’s ionic framework can produce a<br />
coherent multiphonon transition without any additional smallness. We have developed a method<br />
which allows us to describe the evolution <strong>of</strong> the deformation parameter up to the level crossing<br />
point, followed by electronic intershell transitions. The process is analogous to internal<br />
conversion in polyatomic molecules, but generally involves more than a single pair <strong>of</strong> electronic<br />
orbitals. It is found that the corresponding relaxation time indeed can be quite short.<br />
As an application, we have performed a model calculation for aluminum clusters. This was<br />
motivated by recent experimental work [1] which used time-resolved two-photon photoemission<br />
<strong>of</strong> Aln¯ (n=6-15) to demonstrate that the intermediate electronic state decays within a few<br />
hundred femtoseconds in all <strong>of</strong> the above cluster sizes, even in the closed-shell Al13¯. Our<br />
results are in agreement with the observed lifetime.<br />
This work was supported by the NSF (V.V.K.), a NATO Collaborative Linkage Grant (V.V.K.<br />
and Yu.N.O.), and DARPA (V.Z.K.).<br />
References<br />
[1] P. Gerhardt, M. Niemietz, Y. D. Kim, G. Ganteför, Chem. Phys. Lett. 382, 454 (2003).<br />
67
B - 28<br />
68<br />
Femtosecond Laser-Induced Fusion <strong>of</strong> Fullerenes Inside Clusters<br />
Martin Hedén, Klavs Hansen, Eleanor E. B. Campbell<br />
Department <strong>of</strong> Physics, Göteborg University, SE-41296 Göteborg, Sweden<br />
The interaction <strong>of</strong> fullerene molecules with femtosecond laser radiation has been the subject<br />
<strong>of</strong> much interest in recent years. One interesting observation is the clear separation <strong>of</strong> different<br />
ionisation mechanisms that can be observed as a function <strong>of</strong> the timescale for the excitation [1].<br />
We have shown that for intermediate timescales (ca. 70-300 fs) the ionisation can be largely<br />
regarded as a thermal electron emission from the equilibrated hot electron system before energy<br />
is transferred to the nuclear degrees <strong>of</strong> freedom [2]. Interesting dynamics have also been<br />
observed in collisions between fullerenes leading to molecular fusion <strong>of</strong> the collision partners<br />
and the formation <strong>of</strong> a metastable larger fullerene that subsequently decays by the emission <strong>of</strong><br />
C2 molecules [3].<br />
In this contribution we combine these two topics <strong>of</strong> recent research interest and show that it is<br />
possible to induce molecular fusion <strong>of</strong> fullerenes that are weakly (van der Waals) bonded in<br />
molecular clusters. Fig. 1. Shows a typical mass spectrum <strong>of</strong> the clusters after laser irradiation.<br />
The fragmentation pattern is clearly reminiscent <strong>of</strong> C2 emission from a large fullerene-like<br />
structure. We show that this observation is consistent with our knowledge <strong>of</strong> both the ionisation<br />
mechanisms <strong>of</strong> C60 on irradiation with fs laser pulses and with our knowledge <strong>of</strong> the energetic<br />
threshold for fullerene fusion and the C2 decay <strong>of</strong> large fullerenes. It is shown that substantial<br />
atomic rearrangement can take place on a timescale shorter than that needed for the complete<br />
destruction <strong>of</strong> the highly excited cluster. This is different for the observations made in<br />
experiments where fullerene clusters are collided with highly charged ions [4]. Reasons for the<br />
difference will be discussed.<br />
N<br />
Figure 1. Time-<strong>of</strong>-flight mass spectrum from fullerene clusters after excitation with a 200 fs laser pulse.A distribution<br />
<strong>of</strong> fragment masses is seen corresponding to each cluster size, with a mass separation <strong>of</strong> the fragments in each<br />
distribution <strong>of</strong> C2. This is a clear indication that the clusters have ionised and then had time for extensive atomic<br />
rearrangement to form a single large fullerene-like structure before the original clusters completely disintegrate.<br />
References<br />
counts<br />
10000<br />
1000<br />
60 80 100 120 140 160 180 200 220 240 260 280 300<br />
[1] E.E.B. Campbell, K. Hansen, K. H<strong>of</strong>fmann, G. Korn, M. Tchaplyguine, M. Wittmann, I.V. Hertel,<br />
Phys. Rev. Lett., 84 2128 (2000)<br />
[2] K. Hansen, K. H<strong>of</strong>fmann, E.E.B. Campbell, J. Chem. Phys. 119 2513 (2003).<br />
[3] E.E.B. Campbell, A.V. Glotov, A. Lassesson, R.D. Levine, C.R. Physique 3 (2002) 341<br />
[4] B. Manil, L. Maunoury, B. A. Huber, J. Jensen, H. T. Schmidt, H. Zettergren, H. Cederquist, S.<br />
Tomita and P. Hvelplund, Phys. Rev. Lett. 21 (2003) 215504
Femtosecond photoelectron spectroscopy <strong>of</strong> sodium clusters<br />
Abdollah Malakzadeh, Christian Hock, Christ<strong>of</strong> Bartels, Raphael Kuhnen and Bernd v. Issendorff<br />
Fakultät für Physik, <strong>Universität</strong> Freiburg, H.Herderstr. 3, 79104 Freiburg, Germany<br />
B - 29<br />
Recently we have shown that the electron gas in a free sodium cluster can be heated by a<br />
single fs-laser pulse to temperatures high enough for thermal electron emission to occur [1,2].<br />
This emission can be described by a simple model: the laser excites the collective motion <strong>of</strong> the<br />
electrons (the plasmon), which after a very short time (a few fs) decays into single electron-hole<br />
excitations. Due to the strong electron-electron interaction within a short time this nonthermal<br />
energy distribution <strong>of</strong> the electrons is transformed into a thermal one. The electron gas then<br />
cools by electron-phonon coupling.<br />
Time-resolved pump-probe photoelectron and phot<strong>of</strong>ragmentation spectroscopy has been<br />
applied to measure the electron-phonon-coupling constant as a function <strong>of</strong> cluster size. This has<br />
been done using relatively long laser pulses (τ ≈ 200 fs). In order to obtain more information<br />
about the early stages <strong>of</strong> the excitation, shorter laser pulses are necessary. Therefore a NOPA<br />
(noncolinear optical parametric amplifier) has been constructed, which allows the production <strong>of</strong><br />
wavelength tunable, short (τ < 50 fs) laser pulses, as well as a hollow capillary compressor.<br />
The performance <strong>of</strong> these devices and first results for sodium clusters are discussed.<br />
References<br />
[1] R.Schlipper, R. Kusche, B.v.Issendorff and H.Haberland, App. Phys. A. 72, 255 (2001)<br />
[2] M.Maier, M. Astruc H<strong>of</strong>fmann, and B.v. Issendorff, NJP 5, 3 (2003)<br />
69
B - 30<br />
70<br />
Photoelectron Spectroscopy on Small, Size Selected, Neutral Silver<br />
Clusters Embedded in Helium Droplets<br />
Andreas Przystawik, Paul Radcliffe, Josef Tiggesbäumker, Karl-Heinz Meiwes-Broer<br />
Institut für Physik, <strong>Universität</strong> Rostock, <strong>Universität</strong>splatz 3, 18051 Rostock, Germany<br />
Experiments on neutral clusters are <strong>of</strong>ten hampered by a broad distribution <strong>of</strong> cluster sizes.<br />
Therefore most <strong>of</strong> the work concerning the electronic structure <strong>of</strong> clusters is performed with<br />
charged particles, where one can prepare a molecular beam <strong>of</strong> species with a certain number <strong>of</strong><br />
atoms. We present a possibility to exploit absorption resonances to select a cluster size for<br />
excitation and ionization from the neutral beam.<br />
This technique is used to record two-photon photoelectron spectra <strong>of</strong> small silver clusters grown<br />
in helium nanodroplets by the pickup method. We derive information on both, the cluster and its<br />
electronic structure, and the interaction with the helium environment. An analysis <strong>of</strong> the spectra<br />
recorded at different wavelengths shows that all investigated systems undergo a rapid relaxation<br />
on a picosecond timescale to the lower edge <strong>of</strong> the broad excitation, see figure 1.<br />
One possibility <strong>of</strong> helium pickup sources is to prepare clusters in high spin states as already<br />
demonstrated with alkali clusters on the surface <strong>of</strong> droplets [1]. Despite the lack <strong>of</strong> selectivity in<br />
favor <strong>of</strong> high spin states when growing the clusters inside the droplet we can clearly detect<br />
silver dimers in triplet states not present in gas phase spectroscopy.<br />
Figure 1. Schematic diagram <strong>of</strong> the ionization dynamics <strong>of</strong> Ag 8 [2]. After excitation to the unoccupied band E *<br />
roughly 4.0 eV above the ground state, the cluster quickly relaxes to the lower edge EL. In a R2PI<br />
experiment, ionization occurs from this long-living level.<br />
References<br />
[1] P. Claas, D. Schumacher, and F. Stienkemeier, Phys. Rev. Lett. 92, 013401 (2004).<br />
[2] P. Radcliffe et al., Phys. Rev. Lett. 92, 173403 (2004).
Signatures <strong>of</strong> the Giant Dipole Resonance in the Response <strong>of</strong> Metal<br />
Clusters for Strong-Field Dual-Pulse Excitation<br />
Thomas Fennel, Tilo Döppner, Josef Tiggesbäumker and Karl-Heinz Meiwes-Broer<br />
Institut für Physik, <strong>Universität</strong> Rostock, <strong>Universität</strong>splatz 3, 18051 Rostock , Germany<br />
B - 31<br />
The response <strong>of</strong> metal clusters irradiated with a sequence <strong>of</strong> two femtosecond laser pulses is<br />
strongly dependent on the optical delay between the pulses. Recent experiments have shown<br />
that the adjustment <strong>of</strong> the delay provides a powerful way to control the coupling <strong>of</strong> strong laser<br />
radiation to finite systems. Both the yield <strong>of</strong> highly charged ions [1] as well as the kinetic<br />
energy <strong>of</strong> emitted electrons is strongly enhanced for a particular optimal delay. The dynamics <strong>of</strong><br />
the signals is much more pronounced compared to earlier measurements using stretched<br />
pulses [2].<br />
For the investigation <strong>of</strong> the time-dependent interaction <strong>of</strong> dual pulses with simple metal clusters<br />
numerical simulations have been performed using Thomas-Fermi-Vlasov molecular dynamics<br />
(TFV-MD) [3]. The semiclassical treatment allows a fully three-dimensional microscopic<br />
simulation <strong>of</strong> the laser-cluster interaction and provides a reasonable description <strong>of</strong> delocalized<br />
electrons in the cluster groundstate as well as the violent nonlinear response to a strong field<br />
close to TDLDA.<br />
Simulations on Na55 and Ag55 show that also in the strong field regime the most effective<br />
absorption is caused by resonant excitation <strong>of</strong> multi-plasmon modes. The calculations are in<br />
qualitative agreement with the measurements and clearly reproduce an optimal optical delay for<br />
enhanced ionization <strong>of</strong> the cluster [1], see Fig. 1, as well as a strong energy enhancement in the<br />
electron emission.<br />
Figure 1. (a) Calculated average charge <strong>of</strong> emitted ions after dual-pulse excitation <strong>of</strong> Na55 as a function <strong>of</strong><br />
the optical delay. Both pulses have a width <strong>of</strong> 50fs at a wavelength <strong>of</strong> 800nm. (b) Measured normalized<br />
dual-pulse signals <strong>of</strong> Ag 5+ from the explosion <strong>of</strong> silver clusters in helium droplets, resulting from the<br />
excitation with 130 fs pulses. Taken from Ref. [1].<br />
References<br />
[1] Döppner, Fennel et al., Phys. Rev. Lett, in press<br />
[2] Köller, Schumacher, Köhn et al., Phys. Rev. Lett. 82:3783, 1999<br />
[3] Fennel, Bertsch and Meiwes-Broer et al., Eur. Phys. J. D 29:367, 2004<br />
71
B - 32<br />
Fragmentation <strong>of</strong> small alkali cluster attached to helium nanodroplets<br />
72<br />
Patrick Claas 1 , Georg Droppelmann 1 , Claus-Peter Schulz 2 and Frank Stienkemeier 1<br />
1 Fakultät für Physik, <strong>Universität</strong> Bielefeld, <strong>Universität</strong>sstr. 25, D-33615 Bielefeld, Germany<br />
email: franks@physik.uni-bielefeld.de<br />
2 Max-Born-Institut, Max-Born-Str. 2a, D-12489 Berlin, Germany<br />
We use helium nanodroplet isolation (HENDI) to form cold small alkali clusters. In<br />
particular, potassium atoms are picked up successively by superfluid helium droplets in order to<br />
aggregate to clusters at temperatures <strong>of</strong> 380 mK. In a femtosecond pump-probe setup we<br />
determine fragmentation times <strong>of</strong> the clusters upon electronic excitation. In contrast to earlier<br />
experiments on free clusters (cf. Figure 1) we find substantially longer times in the<br />
fragmentation processes. The following aspects have to be considered: (a) population <strong>of</strong> highspin<br />
states [3]; (b) missing thermal activation because <strong>of</strong> the low temperature; (c) cage effects<br />
by the helium environment. Studies performed at different photon energies, droplet sizes, etc.<br />
allow a closer look at the fragmentation mechanism and the items given above.<br />
Furthermore first results are presented on the formation <strong>of</strong> complexes <strong>of</strong> alkali clusters with<br />
foreign atoms or molecules (e.g. H2O) attached to helium droplets.<br />
decay time [ps]<br />
Figure 1.: Fragmentation times upon femtosecond laser excitation <strong>of</strong> potassium clusters K n attached to helium<br />
nanodroplets as a function <strong>of</strong> cluster size. As a comparison results <strong>of</strong> gas-phase clusters by Wöste et al. are also<br />
included.<br />
References<br />
10<br />
1<br />
2 4 6 8 10<br />
cluster size n<br />
[1] H. Kühling et al., J. Phys. Chem. 98, 6679 (1994).<br />
[2] A. Ruff et al., Z. Phys. D 37, 175 (1996).<br />
[3] C. P. Schulz, et al., Phys. Rev. Lett. 92(1), 013401 (2004) .<br />
this work, 1.55eV, K<br />
this work, 1.47eV, K<br />
[1], 1.47 eV, K<br />
[1], 2.94 eV, K<br />
[2], 2.92 eV Na
Embedding <strong>of</strong> Na clusters in raregas matrices<br />
F. Fehrer 1 , P.-G. Reinhard 1 , E. Suraud 2 , M. Dinh 2 , G. Bousquet 2<br />
1 Institut für theoretische Physik, <strong>Universität</strong> Erlangen, Staudtstrasse 7, D-91058 Erlangen, Germany<br />
2 Laboratoire de Physique Quantique, Universite Paul Sabatier, 118 Route de Narbonne,<br />
F-31062 Toulouse, cedex, France<br />
B - 33<br />
We have developed a microscopic model for the description <strong>of</strong> a Na-cluster embedded in a<br />
raregas (Rg) substrate. The cluster valence electrons are treated at the level <strong>of</strong> TDLDA. The Rgatoms<br />
are considered as classical point-particles interacting with the cluster-electrons via local<br />
pseudopotentials. In order to describe the polarization <strong>of</strong> the raregas, we ascribe each Rg-atom a<br />
time-dependent dipolemoment. A short range repulsive Rg-core-potential together with a term<br />
taking the vdW-interaction into account is added. The model is calibrated to reproduce bindingproperties<br />
<strong>of</strong> the NaRg molecule and bulk Rg.<br />
We first study the influence <strong>of</strong> the Rg on the optical response <strong>of</strong> the cluster. We then investigate<br />
the coupled nonlinear dynamics <strong>of</strong> cluster and matrix following a strong laser excitation.<br />
73
B - 34<br />
Relaxation Dynamics <strong>of</strong> Optically Excited States <strong>of</strong> Ag Cluster Anions<br />
74<br />
Markus Engelke, Marco Niemietz, Young Dok Kim, Gerd Ganteför<br />
Fachbereich Physik, <strong>Universität</strong> <strong>Konstanz</strong>, 78457 <strong>Konstanz</strong>, Germany<br />
http://www.clusterphysik.uni-konstanz.de/<br />
For bulk metals, optically excited electronic states can relax within few tens <strong>of</strong><br />
femtoseconds due to very fast Auger-like electron-electron scattering processes. As the size <strong>of</strong> a<br />
particle decreases, changes in relaxation dynamics <strong>of</strong> optically excited states are observed [1,2].<br />
Using Time-Resolved Two-Photon Photoemission (TR-PPE) spectroscopy, relaxation times <strong>of</strong><br />
optically excited states <strong>of</strong> Ag cluster anions consisting <strong>of</strong> less than 22 atoms (pump photon<br />
energy <strong>of</strong> 1.5 eV) were determined. For Ag18 - , Ag19 - and Ag21 - , relaxation times amount to about<br />
500 femtoseconds, which are significantly longer than those <strong>of</strong> d-metal clusters consisting <strong>of</strong><br />
less than 8 atoms [3]. The long life times <strong>of</strong> the excited states <strong>of</strong> these Ag cluster anions can be<br />
explained by lower density <strong>of</strong> states above the upper levels <strong>of</strong> the non-excited electrons within<br />
the pump photon energy in these clusters, caused by a large gap between 2s and 1f electronic<br />
shells, i.e. electronic shell configurations significantly affect the electron relaxation dynamics.<br />
-<br />
Ag18 Intensity (a.u.)<br />
References<br />
0 fs<br />
133 fs<br />
266 fs<br />
932 fs<br />
1,9 ps<br />
12,9 ps<br />
48,6 ps<br />
0 1 2<br />
Binding Energy (eV)<br />
Figure 1. TR-PPE spectra <strong>of</strong> Ag 18 - . A distinct peak can<br />
be observed at a binding energy <strong>of</strong> about 1.3 eV,<br />
accompanying broad states at higher binding energies.<br />
The state at 1.3 eV can be attributed to the excitation <strong>of</strong><br />
an electron in the HOMO to an unoccupied state. As the<br />
delay between pump and probe photons increases, the<br />
signals between 1.2eV - 2.5 eV attenuate. By assuming<br />
an exponential decay <strong>of</strong> the excited state, the lifetime is<br />
estimated to be about 420 fs.<br />
[1] J.R.R. Verlet, A.E. Bragg, A. Kammrath, O. Cheshnovsky, and D.M. Neumark,<br />
J. Chem. Phys. 121, 10015 (2004).<br />
[2] M. Niemietz, P. Gerhardt, G. Ganteför and Y. D. Kim, Chem. Phys. Lett. 380, 99 (2003).<br />
[3] N. Pontius, M. Neeb, W. Eberhardt, G. Lüttgens, P. S. Bechthold, Phys. Rev. B 67, 354251 (2003)<br />
and references therein
Theoretical studies <strong>of</strong> ultrafast processes in clusters and metalbiomolecule<br />
complexes<br />
Roland Mitrić, Vlasta Bonačić-Koutecký<br />
B - 35<br />
Humboldt <strong>Universität</strong> zu Berlin, Institut für Chemie, Brook-Taylor-Strasse 2, D-12489 Berlin, Germany<br />
Our theoretical approach for exploration <strong>of</strong> ultrafast dynamics is based on combination <strong>of</strong><br />
the adiabatic and nonadiabatic ab initio MD ’on the fly’ with the Wigner distribution approach<br />
and permits to include all degrees <strong>of</strong> freedom. We show that it allows to accurately simulate<br />
femtosecond spectra in complex systems involving both ground and excited electronic states<br />
and to reveal the underlying dynamical processes [1].<br />
This will be illustrated on the following examples:<br />
i) Real time investigation <strong>of</strong> the ultrafast processes in the ground and excited states <strong>of</strong> noble<br />
metal clusters can provide insights relevant for understanding <strong>of</strong> their reaction dynamics. We<br />
present the simulation <strong>of</strong> the fs signals <strong>of</strong> the Ag2Au − /Ag2Au/Ag2Au + [2] system in the<br />
framework <strong>of</strong> the NeNePo spectroscopy. This allowed us to establish conditions under which<br />
the geometric relaxation can be distinguished from the IVR process which plays a crucial role<br />
for the stabilization <strong>of</strong> the complexes between the cluster and reacting molecule (e. g. O2 or<br />
CO). Study <strong>of</strong> cluster size effects on the dynamics in the excited electronic states <strong>of</strong> anionic<br />
clusters have been explored on the example <strong>of</strong> the Au5 − and Au7 − with the perspective to<br />
identify the dynamical processes in the time resolved photoelectron spectra. Based on these<br />
studies we propose the resonant two photon NeNePo technique, involving anionic excited<br />
states, which may serve for control <strong>of</strong> the reactivity <strong>of</strong> clusters.<br />
ii) Interplay between nonradiative and radiative relaxation processes play an important role in<br />
the design <strong>of</strong> efficient light-emitting materials. Influence <strong>of</strong> nonadiabaticity on the ultrafast<br />
excited state dynamics in the third 1 1 B1 electronic state <strong>of</strong> Na3F cluster has been investigated<br />
employing the ab initio MD ’on the fly’ in the framework <strong>of</strong> TDDFT [1,3] and CI methods. The<br />
simulated pump-probe signals exhibit characteristic oscillations at early times which are in good<br />
agreement with experimental results [3]. At later times simulations <strong>of</strong> the nonadiabatic<br />
dynamics in the framework <strong>of</strong> the CI method allow us to estimate the nonradiative lifetime.<br />
iii) Formation <strong>of</strong> complexes between silver clusters and tryptophan can possibly lead to<br />
enhancement <strong>of</strong> the light absorption and to fluorescence. Therefore, the influence <strong>of</strong> Ag + cation<br />
on the conformation and optical properties <strong>of</strong> tryptophan has been investigated. For this purpose<br />
we employ the combination between semi-empirical CI methods with the MD ”on the fly”.<br />
These studies serve as a starting point for the exploration <strong>of</strong> emissive properties and ultrafast<br />
dynamics.<br />
References<br />
[4] V. Bonačić-Koutecký, R. Mitrić, Chem. Rev., 105, 11 (2005).<br />
[5] T. M. Bernhardt, J. Hagen, L. D. Socaciu, J. Le Roux, D. Popolan, M. Vaida, L.Wöste, R.<br />
Mitrić, V. Bonačić-Koutecký , A. Heidenreich, J. Jortner, ChemPhysChem, 6, 243 (2005).<br />
[6] M. C. Heitz, G. Durand, F. Spiegelman, C. Meier, R. Mitrić, V. Bonačić-Koutecký, J. Chem.<br />
Phys., 121, 9906 (2004).<br />
75
B - 36<br />
76<br />
Rapid Alloying in binary Clusters: A Molecular Dynamics Study<br />
Y. Shimizu, T. Kobayashi, K. S. Ikeda and S. Sawada<br />
Ritsumeikan University, Kwansei Gakuin University<br />
Dynamics <strong>of</strong> surface atoms penetrating into microclusters is investigated in connection with<br />
the very rapid alloying (RA) in metal microclusters. RA was experimentally discovered by<br />
Yasuda and Mori for various types <strong>of</strong> nano-sized binary metal clusters. In short, RA is a<br />
manifestation <strong>of</strong> an unexpectedly fast diffusion <strong>of</strong> solute atoms into a host cluster, which is<br />
controlled by the magnitude <strong>of</strong> heat <strong>of</strong> solution and size <strong>of</strong> a cluster. Isothermal molecular<br />
dynamics simulation is done to investigate the mechanism <strong>of</strong> RA.<br />
In particular, we put our focus upon a cooperative interplay between atomic rearrangement<br />
along a cluster surface and that along radial direction <strong>of</strong> a cluster.<br />
Our results are summarized in the following two points. The dependence <strong>of</strong> the alloying and<br />
that <strong>of</strong> radial diffusion upon negative heat <strong>of</strong> solution are elucidated. It is found that dependency<br />
<strong>of</strong> the “alloying rate” upon the negative heat <strong>of</strong> solution and the size <strong>of</strong> clusters reproduced the<br />
qualitative features observed in the experiments. To quantify the dependence <strong>of</strong> atomic<br />
rearrangement dynamics upon temperature, the activation process <strong>of</strong> diffusive motion <strong>of</strong> atoms<br />
is analyzed.<br />
Although the activation energy <strong>of</strong> radial diffusion is about two times as large as that <strong>of</strong><br />
surface diffusion, there are circumstantial evidences that the latter process controls the former<br />
one. In that sense the rapid radial diffusion <strong>of</strong> a surface atom into a cluster is caused by the<br />
surface diffusion unlike the usual diffusion in bulk solid. In order to clarify the mechanism<br />
converting the active surface motion into the rapid radial diffusion, we numerically enumerate<br />
reaction paths. We found some candidates <strong>of</strong> characteristic collective motion which would<br />
effectively induce the rapid radial diffusion in terms <strong>of</strong> the surface activity.<br />
These two results suggest that surface atoms diffuse into the inside <strong>of</strong> the cluster due to the<br />
accumulation <strong>of</strong> active surface motion during long-time dynamics beyond a microsecond, even<br />
though the cluster is almost in solid-phase. Whilst diffusion due to the mechanism is crucial for<br />
the onset <strong>of</strong> RA, the same atomistic process is similarly expected not only for binary clusters,<br />
but also for monotonous ones. It leads us to an idea that a microcluster can be viewed as a<br />
dynamic material in which a transport <strong>of</strong> atoms between the surface area and the core region is<br />
continually induced in the course <strong>of</strong> long time scale.
Magnetism<br />
77
Electronic and Magnetic Properties <strong>of</strong><br />
Lanthanide Organometallic Clusters<br />
Atsushi Nakajima<br />
Department <strong>of</strong> Chemistry, Faculty <strong>of</strong> Science and Technology, Keio University & JST-CREST,<br />
3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan<br />
B - 37<br />
Binary systems are very important to create functionality <strong>of</strong> materials, and binary clusters<br />
consisting <strong>of</strong> a few to hundreds atoms provide microscopic viewpoints toward chemical<br />
bonding, geometry, and electronic structures including spin states. For metal and organic<br />
ligands, a variety <strong>of</strong> 1D, 2D, and 3D structures are formed depending on their combinations, and<br />
they exhibit novel electronic properties, such as electron delocalization and multiple charge<br />
transfers.<br />
With the aid <strong>of</strong> proper organic ligands, 1D structures are preferably formed in gas phase<br />
reaction. For example, Eum(C8H8)n sandwich clusters were produced in gas phase by mixing the<br />
vapor <strong>of</strong> europium (Eu) atoms and 1, 3, 5, 7-cyclooctatetraene (C8H8) molecules and 18-layered<br />
clusters were produced at maximum, which is about 8 nm length. With photoionization and<br />
photoelectron spectroscopies, formation mechanism and electronic structures will be presented<br />
in the viewpoint <strong>of</strong> sequential reactions with harpoon mechanism.<br />
In the design <strong>of</strong> molecular magnetic materials, furthermore, a subject to conquer is how to<br />
align the spin in the cluster. One-dimensional sandwich clusters are an interesting target since<br />
their magnetism should reflects geometric anisotropy and the condition <strong>of</strong> electronic spins on<br />
each layer. Stern-Gerlach type magnetic deflection measurements were performed for two types<br />
<strong>of</strong> multiple sandwich clusters: vanadium-benzene Vn(C6H6)n+1 and terbium-cyclooctatetraene<br />
Tbn(C8H8)n+1. Beams <strong>of</strong> Vn(C6H6)n+1 clusters (n = 1-4) showed symmetric broadening induced<br />
by the inhomogeneous field, indicating free spin behavior similar to that displayed by isolated<br />
paramagnetic atoms. By contrast, beams <strong>of</strong> Tbn(C8H8)n+1 clusters displayed one-sided deflection,<br />
indicating that fast spin relaxation occurs within the clusters. The difference in the magnetic<br />
deflection behavior exhibited by these two systems is explained by their electronic structures,<br />
specifically the bonding characteristics between metal atoms and ligand molecules.<br />
References<br />
[1] A. Nakajima, K. Kaya “A novel network structure <strong>of</strong> organometallic clusters”<br />
JPC A 104, 176 (2000).<br />
[2] S. Nagao, A. Nakajima, K. Kaya “Multiple-decker sandwich poly-ferrocene clusters”<br />
JACS 122, 4221 (2000).<br />
[3] K. Judai, K. Yagi, S. Yabushita, A. Nakajima, K. Kaya “A s<strong>of</strong>t-landing experiment <strong>of</strong> organometallic<br />
cluster ions: infrared spectroscopy <strong>of</strong> V(benzene)2 in Ar matrix” CPL 334, 277 (2001).<br />
[4] K. Miyajima, T. Yasuike, S. Yabushita, A. Nakajima, K. Kaya “The quasi-band electronic structure<br />
<strong>of</strong> Vn(Benzene)n+1 clusters” JPC A 106, 10777 (2002).<br />
[5] K. Miyajima, A. Nakajima, S. Yabushita, M. B. Knickelbein, and K. Kaya “Ferromagnetism in onedimensional<br />
vanadium-benzene sandwich clusters” JACS 126, 13202 (2004).<br />
[6] N. Hosoya, R. Takegami, K. Miyajima, M. B. Knickelbein, S. Yabushita, A. Nakajima “Lanthanide<br />
organometallic sandwich nanowires: formation mechanism” JPC A (Letter) in press.<br />
[7] K. Miyajima, M. B. Knickelbein, A. Nakajima “Stern-Gerlach studies <strong>of</strong> organometallic sandwich<br />
lusters” EPJD in press.<br />
79
B - 38<br />
80<br />
Mn clusters: a nanoscale magnetic transition<br />
Sudha Srinivas and Koblar Alan Jackson<br />
Department <strong>of</strong> Physics, Central Michigan University, Mount Pleasant, Michigan 48859, USA<br />
Small Mn clusters exhibit remarkable magnetic behavior. Early ESR experiments[1] found<br />
the smallest clusters (n=2-5) to be ferromagnetic (FM), with total net spin corresponding to 5 µB<br />
per atom, the Hund’s rule value for an isolated Mn atom. Later Stern-Gerlach measurements[2]<br />
found larger clusters (n>12) to have very small net moments. For example, Mn13 was found to<br />
have a net moment <strong>of</strong> only 3 µB for the entire cluster. Our recent calculations[3,4] explain that<br />
these data reflect a transition in magnetic ordering as a function <strong>of</strong> cluster size, occurring at n=7<br />
atoms. Specifically, the FM arrangements <strong>of</strong> the atomic spins favored in smaller clusters give<br />
way to antiferromagnetic (AF) arrangements in larger clusters. The calculations indicate that the<br />
FM → AF transition occurs at n=7, in agreement with experimental data, and is driven by a<br />
large change in the relative energies <strong>of</strong> the FM and AF structures. For n
The magnetic moments <strong>of</strong> isolated metal clusters<br />
Gereon Niedner-Schatteburg 1 and Wilfried Wurth 2<br />
1 Fachbereich Chemie, TU Kaiserslautern, Germany (gns@chemie.uni-kl.de)<br />
2 Institut für Experimentalphysik, <strong>Universität</strong> Hamburg, Germany (wilfried.wurth@desy.de)<br />
B - 39<br />
Within the last fiveteen years X-ray Magnetic Circular Dichroism (XMCD) has made itself<br />
useful in solid state physics and in surface science [2] since it allows for the elucidation <strong>of</strong><br />
magnetic properties that would be unavailable otherwise. For chemists XMCD has become a<br />
valuable tool when investigating paramagnetic organometalic and coordination compounds [2].<br />
In a few cases even paramagnetic metalloproteins have been studied successfully [3]. Only<br />
recently size selected iron clusters became subject <strong>of</strong> XMCD measurements [4]. All <strong>of</strong> these<br />
studies, however, have utilized condensed phase samples. Substrates and solvents may exert<br />
decisive but unknown influence on the magnetic properties <strong>of</strong> deposited and desolved samples,<br />
respectively. It is mandatory to identify suitable model systems for direct investigation and void<br />
<strong>of</strong> such an interference.<br />
We propose to apply XMCD to isolated gas phase metal clusters <strong>of</strong> selected sizes. This novel<br />
experimental scheme shall allow for determination <strong>of</strong> total magnetic moments as arising<br />
through spin and orbit contributions. Temperature tuning shall enable the recording <strong>of</strong><br />
magnetization curves.<br />
This shall be enabled through application <strong>of</strong> circularly polarized x-ray synchrotron radiation<br />
(600eV) to isolated gas phase transition metal clusters which have been size selected and stored<br />
in an ion trap [5,6] under high vacuum.<br />
The talk shall outline the basic features <strong>of</strong> the proposed scheme and it is going to suggest a<br />
particular way to carry out actual experiments.<br />
References<br />
[1] G. Schütz et al., Phys. Rev. Lett. 58, 737 (1987); C. T. Chen, N.V. Smith, and F. Sette, Phys. Rev.<br />
B 43, 6785 (1991); B. T. Thole et al., Phys. Rev. Lett. 68, 1943 (1992); M. Altarelli, Phys. Rev. B<br />
47, 597 (1993); C. T. Chen et al., Phys. Rev. B 48, 642 (1993); Y. U. Idzerda et al., Surf. Science<br />
287/288, 741 (1993)<br />
[2] S. P. Cramer in: ACS Symposium series Vol. 858 (2003)<br />
[3] J. Van Elp. et al., Proc. Nat. Acad. Sci. U.S.A. 90, 9664 (1993)<br />
[4] S. T. Lau, A. Föhlisch, R. Nietubyc, M. Reif, and W. Wurth, Phys. Rev. Lett. 89, 057201 (2002)<br />
[5] G. Niedner-Schatteburg and V. E. Bondybey, Chem. Rev. 100, 4059 (2000)<br />
[6] A. Lagutschenkov et al., Poster, S 3 C, Brand 2005<br />
81
Materials<br />
83
B - 39<br />
84
Intensity<br />
10000<br />
8000<br />
6000<br />
4000<br />
2000<br />
Stable Clusters <strong>of</strong> Layered Semiconductors Prepared by Laser<br />
Ablation<br />
M. Galak 1 , O. Yeschenko 1 , I. Dmitruk 1 , V. Romanyuk 2 , A. Kasuya 2<br />
540<br />
500 600 700 800 900<br />
wavelength, nm<br />
B - 40<br />
1 Department <strong>of</strong> Physics, National Taras Shevchenko University<strong>of</strong> Kyiv, prosp. akad. Glushkov 2, Kyiv,<br />
01022, Ukraine<br />
2 Center for Interdisciplinary Research, Tohoku University, Sendai, 980-8578, Japan<br />
The aim <strong>of</strong> the research presented is to investigate cluster formation under pulsed laser<br />
ablation <strong>of</strong> layered semiconductors. Rapid evaporation <strong>of</strong> material provoked by high intensity<br />
laser beam creates favorable conditions for cluster formation. Recent success in investigations<br />
<strong>of</strong> new ultra-stable material compositions [1] led us to search for clusters with elevated stability<br />
<strong>of</strong> other materials.<br />
Films consisting <strong>of</strong> HgI2 and PbI2 nanoparticles (NP) have been prepared by pulsed N2 laser<br />
ablation. Absorption spectrum shows one broad peak <strong>of</strong> HgI 2 NP and one peak <strong>of</strong> PbI 2 NP<br />
corresponding to wide size distribution. Photoetching technique was used to decrease number <strong>of</strong><br />
large particles. Strong blue shift <strong>of</strong> PL peak <strong>of</strong> NP film caused by quantum size effect is<br />
observed (Fig.1). Semi-empirical structure calculations were performed using the MNDO basis<br />
set in the GAMESS package. The calculation shows that there are few stable clusters <strong>of</strong> HgI2<br />
and PbI2 with atomic masses less than 4000 a.m.u. To confirm theoretical calculations mass<br />
spectra <strong>of</strong> samples <strong>of</strong> HgI2 (Fig. 2) and PbI2 are obtained. Samples for mass-spectroscopy were<br />
prepared at similar conditions and in the same manner as for optical investigations. Peak<br />
positions correspond to stable clusters <strong>of</strong> both materials HgnIm and PbnIm consisting <strong>of</strong> n = 3, m<br />
= 5; n = 4, m = 7; n = 4, m = 9 atoms. There is a good agreement <strong>of</strong> theoretical prediction and<br />
observed peaks in mass spectra.<br />
Figure 1. Photoluminescence spectrum <strong>of</strong> HgI2<br />
stable clasters. Narrow line at 540nm<br />
corresponds to emmision <strong>of</strong> nanoparticles.<br />
References<br />
Figure 2. Mass-spectrum <strong>of</strong> HgnIm clusters<br />
prepared by laser ablation. Numbers in brackets<br />
corresponds to assigned number <strong>of</strong> atoms <strong>of</strong> Hg<br />
and I, respectively.<br />
[1] A.Kasuya, R.Sivamohan, Yu.Barnakov, I.Dmitruk, et al, Nature Materials, No.3 (2004).<br />
85
B - 41<br />
Stable Cluster Motifs For Nanoscale Materials<br />
S. N. Khanna<br />
Physics Department, Virginia Commonwealth University, Richmond, Va. 23284-2000, USA<br />
A major step in creating nanoscale materials with desirable electronic and magnetic<br />
properties is the identification <strong>of</strong> structural motifs that can simultaneously display the stability<br />
requisite for implementation as building blocks and the preservation <strong>of</strong> electronic and magnetic<br />
properties within this motif. Using three different examples (marking different bonding<br />
characteristics), we present our recent results on how by controlling size, composition and<br />
formation conditions, it may be possible to design very stable clusters with desirable traits that<br />
could serve as the building blocks for extended materials.<br />
The first part <strong>of</strong> the work concerns our recent investigations on chromium and iron oxide<br />
clusters. We have shown that by controlling the formation conditions, it is possible to generate<br />
different classes <strong>of</strong> metal-oxide clusters, each with unique electronic and magnetic properties. In<br />
particular, size-selected iron-oxide clusters can oxidize CO and reduce NO and <strong>of</strong>fer<br />
tremendous potential for applications [1].<br />
The second part <strong>of</strong> the work concerns our recent investigations on aluminum halogen clusters. It<br />
is shown that some <strong>of</strong> the acid etching reactions that can lead to very stable aluminum halogen<br />
mixed clusters. The studies provide evidence that Al13 - can act as a superhalogen when<br />
combined with conventional halogens. What is truly remarkable is that a completely new class<br />
<strong>of</strong> poly-halides can be formed by using Al13 - in combination with conventional halogens [2].<br />
Finally, we have just extended our previous work on semiconductor metal clusters [3]. We have<br />
re-examined some <strong>of</strong> rules that govern the stability <strong>of</strong> this important class <strong>of</strong> clusters and found<br />
that the metal-semiconductor bonding obeys simple electron counting rules. Needless to say,<br />
these rules can guide the search <strong>of</strong> new stable clusters.<br />
References<br />
[1] B. V. Reddy and S. N. Khanna, Phys. Rev. Lett. 93, 068301 (2004).<br />
[2] D. E. Bergeron, A. W. Castleman, Jr., T. Morisato and S. N. Khanna, SCIENCE 304, 84 (2004); D.<br />
E. Bergeron, P. J. Roach, A. W. Castleman, Jr., N. O. Jones, and S. N. Khanna, SCIENCE<br />
(Submitted).<br />
[3] S. N. Khanna, B. K. Rao, and P. Jena, Phys. Rev. Lett. 89, 016803 (2002).<br />
86
Passivation, charging and optical properties <strong>of</strong> gold nanoclusters<br />
Hannu Häkkinen<br />
Department <strong>of</strong> Physics, Nanoscience Center, University <strong>of</strong> Jyväskylä, Finland<br />
B - 42<br />
Nanoclusters and nanoparticles are currently a subject <strong>of</strong> intense experimental and<br />
theoretical research efforts due to their unique physical and chemical properties that might be <strong>of</strong><br />
potential use in future nanotechnologies. The properties <strong>of</strong> Gold nanoclusters are extraordinary<br />
sensitive to a number <strong>of</strong> factors, including size, charge state, passivation by inorganic ligands,<br />
and the type and amount <strong>of</strong> impurity atoms. Varying these factors allows one to "tune" or<br />
"functionalize" the electrical, optical and chemical properties in a desired way. This contribution<br />
will discuss phosphine- and thiol-passivated WAu12, Au39 and Au55 clusters in light <strong>of</strong> recent<br />
large-scale density functional simulations. It is shown that the properties <strong>of</strong> the gold core can<br />
easily be controlled by changing the ligand from π-acidic to σ-donating, i.e., by “chemical<br />
charging”. Exchange <strong>of</strong> phosphine ligands to CO molecules is energetically possible for some<br />
<strong>of</strong> the clusters, making them interesting candidates for nanocatalysts for CO oxidation.<br />
Figure 1. Spacefill visualization <strong>of</strong> trimethylphosphine-passivated Au 55 chloride Au 55(PMe 3) 12Cl 6 – a model for the<br />
famous “Schmid cluster” (ref. 1).<br />
References<br />
[1] G. Schmid, Chem. Rev. 92, 1709 (1992).<br />
87
B - 43<br />
88<br />
Deposition <strong>of</strong> Magic Silicon Clusters<br />
Rainer Dietsche, Felix von Gynz-Rekowski, Dong Chan Lim, Nils Bertram, Tim Fischer,<br />
Ignacio Lopez-Salido, Young Dok Kim, and Gerd Ganteför<br />
Fachbereich Physik, <strong>Universität</strong> <strong>Konstanz</strong>, 78457 <strong>Konstanz</strong>, Germany.<br />
http://www.clusterphysik.uni-konstanz.de/<br />
Since the discovery <strong>of</strong> the “supermagic” cluster C60 [1] researchers are fascinated by the<br />
possibility to synthesize new materials consisting <strong>of</strong> stable clusters. Aiming this question we are<br />
investigating small Silicon clusters and evaluating whether these clusters might be suitable as<br />
building blocks for cluster materials. Previous studies on mass-selected cluster anions <strong>of</strong> Silicon<br />
suggests, that clusters containing 4, 6, 7, and 10 Silicon atoms are closed-shell species with<br />
band gaps <strong>of</strong> 1 to 1.5 eV [2][3] indicating relatively inert and stable properties <strong>of</strong> these clusters.<br />
In our experiment “magic” Silicon clusters Si4 and Si7 are produced by a magnetron sputter<br />
source, mass selected and s<strong>of</strong>t landed (Ekin ≤ 0.3 eV/atom) on Highly Oriented Pyrolytic<br />
Graphite (HOPG), amorphous Carbon and Silver. The deposited clusters are studied via<br />
Ultraviolet Photoelectron Spectroscopy (UPS), X-Ray Photoelectron Spectroscopy (XPS), Low<br />
Energy Electron Diffraction (LEED), Auger Electron Spectroscopy (AES) and High-Resolution<br />
Electron Energy Loss Spectroscopy (HREELS). The results are compared to those <strong>of</strong> “nonmagic”<br />
clusters like Si8 and Silicon bulk.<br />
The experimental data indicates that “magic” Silicon clusters do not form bulk material upon<br />
deposition whereas Silicon monomers show bulk like electronic structures. Furthermore the<br />
deposited clusters show no significant reactivity towards Oxygen. However, additional<br />
measurements have to be made.<br />
References<br />
[1] H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl, and R. E. Smalley, Nature 318, 162 (1985).<br />
[2] O. Cheshnovsky, S. H. Yang, C. L. Pettiette, M. J. Craycraft, Y. Liu, and R. E. Smalley, Chem.<br />
Phys. Lett. 138, 119 (1987).<br />
[3] J. Müller, B. Liu, A. A. Shvartsburg, S. Ogut, J. R. Chelikowsky, K. W. M. Siu, K.-M. Ho, and G.<br />
Ganteför, Phys. Rev. Lett. 85, 1666 (2000).
WS and MoS: Magic Clusters and Nanoplatelets studied by PES<br />
N. Bertram, J. Cordes, Young Dok Kim, G. Ganteför<br />
Department <strong>of</strong> Physics, University <strong>of</strong> <strong>Konstanz</strong>, 78457 <strong>Konstanz</strong>, Germany.<br />
http://www.clusterphysik.uni-konstanz.de/<br />
B - 44<br />
MoS and WS are very similar to carbon in the bulk. Thus it is interesting to see whether<br />
layered structures or even fullerenes can be formed out <strong>of</strong> these materials in the nano-regime.<br />
For WS clusters, a series <strong>of</strong> stable triangular platelet structures has been predicted by theory<br />
[1] consisting <strong>of</strong> 6, 10, 15 etc. W atoms forming the plane <strong>of</strong> the triangle and a corresponding<br />
number <strong>of</strong> S atoms located on both sides. WS clusters have now been generated in the PACIS<br />
source and studied by means <strong>of</strong> mass spectroscopy and photoelectron spectroscopy (PES),<br />
supporting the platelet hypothesis. The platelets show an electron affinity around 4 eV and, in<br />
agreement with theory, no electronic gap.<br />
In addition to that, several smaller magic MoS and WS cluster have been studied and very<br />
large electronic gaps (~ 2 eV) have been found for Mo4S6 and W4S6 for example, indicative <strong>of</strong> a<br />
high stability. For MoS, Chevrel phases have been observed, consisting <strong>of</strong> Mo6S8 building<br />
blocks. Due to their high stability, the aforementioned magic clusters are very promising<br />
building blocks for deposition on surfaces and the formation <strong>of</strong> cluster materials.<br />
References<br />
Figure 1. Measured photoelectron spectrum <strong>of</strong> W 4S 6 - and calculated structure <strong>of</strong> Mo4S 6 - by G. Seifert.<br />
Figure 2. Calculated structure <strong>of</strong> MoS-platelet by G. Seifert and Chevrel phase consisting <strong>of</strong> Mo 6S 8.<br />
[1] Gotthard Seifert, Institute for Physical Chemistry, Technical University Dresden, 01062 Dresden,<br />
Germany.<br />
89
Methods<br />
91
PEACE - a new photoelectron action spectroscopy<br />
Shai Ronen, Israel Wolf, Rina Giniger and Ori Cheshnovsky<br />
School <strong>of</strong> Chemistry, the Sackler Faculty <strong>of</strong> Exact Sciences,<br />
Tel Aviv University, Tel Aviv 69978 Israel<br />
B - 45<br />
Neumark and coworkers [1] have pioneered ZEKE spectroscopy on anionic molecules and<br />
clusters. Unfortunately, due to the low cross-section for electron detachment <strong>of</strong> anions at<br />
threshold, this method is very difficult to apply.<br />
We present a new experimental approach, in which the action spectroscopy is recorded with<br />
electrons <strong>of</strong> fixed finite kinetic energy. This approach circumvents some shortcomings <strong>of</strong> the<br />
anionic ZEKE. By working above threshold the cross-section is higher, allowing for higher<br />
signal, and the detection <strong>of</strong> electrons with l>s angular momentum. Neumark and coworkers<br />
have recently developed an equivalent technique based on the velocity map imaging.[2]<br />
The method is based on a modified Magnetic Bottle Photoelectron spectrometer (MBPES). A<br />
tunable laser is used to detach electrons from mass selected anions, which move collinearly with<br />
the 50 cm MBPES drift tube. To avoid Doppler broadening, a low voltage pulse removes the<br />
velocity component <strong>of</strong> anions from the detached electrons[3]. 20 cm downstream, after the<br />
parallelization <strong>of</strong> the electrons in the drift tube, another pulse is applied to reduce their velocity<br />
by a fixed amount. The spectrum is collected by recording the wavelength dependence <strong>of</strong><br />
electron-signal at a predetermined TOF window. This arrival time corresponds to a specific<br />
electron-kinetic energy. We have chosen to call this approach PEACE, denoting PhotoElectron<br />
Action spectroscopy at Constant kinetic Energy.<br />
Our best resolution so far is 1 meV for 10 meV electrons. Below we demonstrate a PEACE<br />
spectrum <strong>of</strong> HgCl- together with the corresponding simulated theoretical spectrum.<br />
References:<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
600<br />
500<br />
400<br />
300<br />
200<br />
100<br />
0<br />
0-12<br />
1-13<br />
Simulated Spectrum<br />
Observed Spectrum<br />
27000 27500 28000 28500 29000 29500 30000 30500<br />
Energy [cm -1 ]<br />
[1] T.N. Kitsopoulos, I. M. Walker, J.G. Loser, D.M. Neumark, Chem. Phys. Letters 159 300 (1989)<br />
[2] Osterwalder, M. J. Nee, J. Zhou, and D. M. Neumark, J. Chem. Phys. 121, 6317 (2004).<br />
[3] R. Giniger T. Hippler, S. Ronen, O. Cheshnovsky, Rev. Sci. Instrum. 72, 2543 (2001)<br />
93
B - 46<br />
94<br />
The effect <strong>of</strong> cluster-gas collisions on the averages <strong>of</strong> charge, energy<br />
and mass <strong>of</strong> an Ar gas cluster ion beam and implications for cluster<br />
induced surface modifications<br />
D. R. Swenson<br />
Epion Corporation, Billerica, MA 01833 USA<br />
Cluster-gas collisions have been the subject <strong>of</strong> several recent papers, but there have been no<br />
studies for large, multi-charged clusters that are typical <strong>of</strong> commercial Gas Cluster Ion Beams<br />
(GCIB). For such large clusters the standard techniques are not adequate because they measure<br />
m/q ratios leaving the mass and charge ambiguous. In a recent paper I reported the first<br />
measurements <strong>of</strong> charge state q, energy E, and mass m for very large Ar clusters as are<br />
commonly used in GCIB processing <strong>of</strong> surfaces [1]. In that paper the average charge <strong>of</strong> the<br />
I<br />
clusters was determined by q = , where I is the electrical current measured by a Faraday<br />
αeΓ<br />
cup, Γ is the flow rate <strong>of</strong> particles in the beam, as measured using a modified Daly detector and<br />
applying particle counting techniques, and α was the measured relative detection efficiency.<br />
The experimental apparatus also included TOF and electrostatic spectrometer measurements, all<br />
for the same pico-amphere-level sample <strong>of</strong> a high intensity Ar GCIB that was accelerated with<br />
30 kV accel potential. This so named “QEM” technique was used to look for the presence <strong>of</strong><br />
multiply charged clusters in the beam and to study the effect <strong>of</strong> cluster-gas collisions. The data<br />
from the experiment consists <strong>of</strong> measurements <strong>of</strong> q , and spectra <strong>of</strong> velocity v and E/q that were<br />
measured for various thicknesses <strong>of</strong> Ar gas that was introduced into a cell immediately<br />
upstream <strong>of</strong> the instruments. The averages v and { E q}<br />
ave are determined from the spectra,<br />
2E<br />
and averages <strong>of</strong> cluster mass and energy are given by E = q{<br />
E q}<br />
ave and by m = . The 2<br />
v<br />
derived averages are strictly valid if the various distributions are uncorrelated. In this paper I<br />
further analyze the data from this experiment and show that a simple analytical model can<br />
predict the main features <strong>of</strong> the data. A more detailed Monte-Carlo simulation is also compared<br />
to the results and to the analytical model, and it is used investigate the limitations <strong>of</strong> the<br />
experimental technique, particularly to what degree correlations affect the average values<br />
derived using the QEM technique. The clusters studied had averages <strong>of</strong> +3.2 charges, 64 keV<br />
energy, and 10,400 atoms at the lowest gas target thickness and were progressively abraded as<br />
the target thickness was increased. It is shown that the mass loss is consistent with a simple<br />
theory that assumes thermalization <strong>of</strong> the collision energy followed by evaporation.<br />
Surprisingly, the clusters lose mass at a greater rate than charge and the N/q ratio decreases as a<br />
result <strong>of</strong> gas collisions. The measurements are important for cluster-surface interactions because<br />
they allow cluster energy and dose to be measured for multi-charged clusters. The theory<br />
developed can be used to understand, predict and optimize the effect <strong>of</strong> gas-cluster collisions on<br />
cluster-surface processing.<br />
References<br />
[1] D.R. Swenson, Nucl. Instr. and Meth. B 222 (2004) 61
B - 47<br />
Computational Electron Spectroscopy – A Powerful Tool for Studies <strong>of</strong><br />
Clusters<br />
Julius Jellinek<br />
Chemistry Division, Argonne National Laboratory, Argonne, Illinois 60439, USA<br />
A new highly accurate scheme for computation <strong>of</strong> the electron energy spectra within the<br />
density functional theory [1] will be sketched, and the results <strong>of</strong> its application to one- and twocomponent<br />
metal clusters will be presented and analyzed. The analysis will include the<br />
evolution <strong>of</strong> the spectra with the cluster size [2-4], structure [4-5], charge state [2-4], and<br />
composition [6]. The computed results will be compared with the available experimental data<br />
[7,8], and their role in the interpretation <strong>of</strong> these data will be illustrated. The discussion will<br />
include analysis <strong>of</strong> the phenomenon <strong>of</strong> size-induced nonmetal-to-metal transition, which defines<br />
the limits <strong>of</strong> miniaturization in nanoelectronics, and the possible relationship between this<br />
phenomenon and the photonic and catalytic properties <strong>of</strong> clusters/nanoparticles.<br />
References<br />
[1] J. Jellinek and P. H. Acioli, J. Chem. Phys. 118, 7783 (2003).<br />
[2] P. H. Acioli and J. Jellinek, Phys. Rev. Lett. 89, 213402 (2002).<br />
[3] J. Jellinek and P. H. Acioli, J. Phys. Chem. A 106, 10919 (2002); 107, 1670 (2003).<br />
[4] J. Jellinek and P. H. Acioli, in Metal Ligand Interaction in Molecular-, Nano- and Macro-Systems<br />
in Complex Environments, N. Russo, D. R. Salahub, and M. Witko (Eds.), Kluwer Academic<br />
Publishers, Dordrecht, 2003, p. 121.<br />
[5] P. H. Acioli and J. Jellinek, Eur. Phys. J. D 24, 27 (2003).<br />
[6] P. H. Acioli and J. Jellinek, to be published.<br />
[7] O. C. Thomas, W. Zheng, S. Xu, and K. Bowen, Phys. Rev. Lett. 89, 213403 (2002).<br />
[8] L.-S. Wang et al., to be published.<br />
95
B - 48<br />
96<br />
Carbon clusters for the calibration in mass spectrometry<br />
Alexander Herlert 1,2 , Sudarshan Baruah 1 , Klaus Blaum 3,4 , Michael Block 4 ,<br />
Ankur Chaudhuri 1 , Frank Herfurth 4 , Alban Kellerbauer 2 , H.-Jürgen Kluge 4 ,<br />
Gerrit Marx 1 , Mannas Mukherjee 4 , Lutz Schweikhard 1 , and Chabouh Yazidjian 2,4<br />
for the ISOLTRAP and SHIPTRAP collaboration<br />
1 Institut für Physik, Ernst-Moritz-Arndt-<strong>Universität</strong> Greifswald, 17487 Greifswald, Germany<br />
2 CERN, Department <strong>of</strong> Physics, 1211 Geneva 23, Switzerland<br />
3 Institut für Physik, Johannes Gutenberg-<strong>Universität</strong> Mainz, 55099 Mainz, Germany<br />
4 GSI, Planckstr. 1, 64291 Darmstadt, Germany<br />
The masses <strong>of</strong> radionuclides are <strong>of</strong> importance in a wide range <strong>of</strong> physics branches [1]:<br />
From nuclear structure studies to tests <strong>of</strong> the Standard model. Penning traps have proven to<br />
allow the mass determination <strong>of</strong> short-lived nuclides with a relative mass uncertainty <strong>of</strong> less<br />
than δm/m=1·10 -8 [2,3] and in case <strong>of</strong> stable nuclides even below 2·10 -11 [4,5].<br />
The principle <strong>of</strong> accurate mass measurements is based on the precise determination <strong>of</strong> the<br />
cyclotron frequency νc=qB/(2πm) <strong>of</strong> the stored ions in the trap. The experimental scheme<br />
monitors the gain in kinetic energy <strong>of</strong> the radial ion motion after excitation with a quadrupolar<br />
radi<strong>of</strong>requency field [6]. For the determination <strong>of</strong> the ion mass, the magnetic field needs to be<br />
calibrated. This is achieved with the measurement <strong>of</strong> the cyclotron frequency <strong>of</strong> an ion with<br />
well-known mass. Here, carbon clusters are the reference particles <strong>of</strong> choice. First, the mass <strong>of</strong> a<br />
12 C atom defines the atomic mass unit. Second, with respect to their mass, carbon clusters Cn are<br />
distributed like a grid on the chart <strong>of</strong> nuclides, where the maximum distance <strong>of</strong> any nuclide to a<br />
carbon cluster is six atomic masses.<br />
In addition, cross-reference measurements allow consistency checks. Thus, carbon clusters<br />
have been used to determine the systematic uncertainties in the mass determination <strong>of</strong> very<br />
short-lived nuclides [7] at the triple trap mass spectrometer ISOLTRAP [8] at ISOLDE/CERN.<br />
For these studies the clusters were produced by laser ablation from a Fullerene target [9]. A new<br />
carbon cluster ion source has recently been installed and will be tested for the upcoming beamtime<br />
period at ISOLDE/CERN. A similar cluster ion source is presently being installed at the<br />
mass spectrometer SHIPTRAP [10] at GSI, which is devoted to mass spectrometry <strong>of</strong> superheavy<br />
nuclides that are delivered from the mass separator SHIP. First results are presented.<br />
References<br />
[1] D. Lunney et al., Rev. Mod. Phys. 75, 1021 (2003).<br />
[2] G. Bollen, Eur. Phys. J. A 15, 237 (2002).<br />
[3] M. Mukherjee et al., Phys. Rev. Lett. 93, 150801 (2004).<br />
[4] R.S. van Dyck et al., Phys. Rev. Lett. 92, 220802 (2004).<br />
[5] S. Rainville et al., Science 303, 334 (2004).<br />
[6] M. König et al., Int. J. Mass Spectrom.Ion Proc. 142, 95 (1995).<br />
[7] A. Kellerbauer et al., Eur. Phys. J. D 22, 53 (2003).<br />
[8] F. Herfurth et al., J. Phys. B: At. Mol. Opt. Phys. 36, 391 (2002).<br />
[9] K. Blaum et al., Anal. Bioanal. Chem. 377, 1133 (2003).<br />
[10] G. Marx et al., Hyperfine Interact. 146/147, 245 (2003).
Photoionisation using Kohn-Sham wave functions<br />
Michael Walter and Hannu Häkkinen<br />
Department <strong>of</strong> Physics, Nanoscience Center, University <strong>of</strong> Jyväskylä, Finland<br />
B - 49<br />
The determination <strong>of</strong> photoionisation cross sections using the Kohn-Sham wave functions<br />
from accurate DFT calculations is studied. The continuum electron is described by an analytical<br />
wave function and the matrix elements are calculated in both in length and velocity form <strong>of</strong> the<br />
dipole operator. The test case <strong>of</strong> water shows excellent agreement between the calculations and<br />
experiment in the ionisation energies if a vertical transition is considered. The cross sections<br />
agree well with the experiment in particular in case <strong>of</strong> the velocity form results. Differences to<br />
the length form and deviations from the experimental asymmetry parameters indicate the<br />
limitations in an analytical description <strong>of</strong> the continuum [3].<br />
Figure 1. State resolved photoionisation cross sections in velocity (full line) and length form (dotted line) for the two<br />
states with the lowest binding energy <strong>of</strong> water. Experimental data from [1] (boxes and triangles) and [2] (circles).<br />
References<br />
[1] M. S. Banna et al, J. Chem. Phys. 84, 4789 (1986).<br />
[2] C. M. Truesdale et al, J. Chem. Phys. 76, 860 (1982).<br />
[3] M.Walter and H. Häkkinen, submitted to Phys. Rev. A<br />
97
B - 50<br />
98<br />
Investigation <strong>of</strong> cluster ions in a Paul trap<br />
Franklin Martinez 1 , Alexander Herlert 1,2 , Gerrit Marx 1 , Hagen Ritter 1 , Lutz Schweikhard 1<br />
1 Institut für Physik, Ernst-Moritz-Arndt-<strong>Universität</strong> Greifswald, 17487 Greifswald, Germany<br />
2 CERN, Department <strong>of</strong> Physics, 1211 Geneva 23, Switzerland<br />
The storage <strong>of</strong> cluster ions in a Penning trap has proven to allow various possibilities <strong>of</strong><br />
experimental investigation [1,2,3,4]. The advantage <strong>of</strong> only an upper but no lower mass limit<br />
and thus trapping <strong>of</strong> particles within a large mass range (even electrons and comparatively<br />
heavy cluster ions) has to be paid by the limitation to only one charge-state polarity and a<br />
reduced access to the stored ions since the Penning trap is mounted inside the bore <strong>of</strong> a<br />
superconducting magnet.<br />
The Paul trap or radi<strong>of</strong>requency trap does not need the strong magnetic field but uses a timevarying<br />
quadrupolar electric field. This allows the storage <strong>of</strong> positively and negatively charged<br />
particles at the same time. In addition the rf trap can be constructed very compact and with<br />
relatively open trap electrodes and therefore axial as well as radial access to the trap is relatively<br />
easy. As an example, a Paul trap has been successfully applied by Parks and coworkers for<br />
electron-diffraction measurements [5].<br />
In the framework <strong>of</strong> experiments on stored clusters similar to the ClusterTrap measurements [1],<br />
the application <strong>of</strong> a Paul trap for future cluster studies is investigated. In a first study the<br />
storage, manipulation and detection <strong>of</strong> atomic clusters are tested. The trapping <strong>of</strong> fullerenes <strong>of</strong><br />
either charge state and their interaction with electrons, ions, neutral atoms as well as photons<br />
will be investigated. The new experimental setup and first results will be presented.<br />
References<br />
[1] L. Schweikhard et al., Eur. Phys. J. D 24, 137 (2003).<br />
[2] C. Walther et al., Phys. Rev. Lett. 83, 3816 (1999).<br />
[3] C. Yannouleas et al., Phys. Rev. Lett. 86, 2996 (2001).<br />
[4] M. Vogel et al., Phys. Rev. Lett. 87, 013401 (2001).<br />
[5] S. Krückeberg et al., Phys. Rev. Lett. 85, 4494 (2000).
Structural characterization <strong>of</strong> large molecules and clusters by<br />
phot<strong>of</strong>ragmentation spectroscopy and scattering experiments.<br />
Michalis Velegrakis<br />
Foundation for Research & Technology – Hellas (FORTH),<br />
Institute <strong>of</strong> Electronic Structure and Laser (IESL)<br />
P.O. Box 1527, Heraklion, GR 71110, Crete<br />
B - 51<br />
The rapid progress in molecular beam techniques, in combination with lasers in the last<br />
years, allowed the production <strong>of</strong> novel molecules in the gas phase such as atomic clusters, metal<br />
oxides and complexes between metal ions and biomolecules. There is growing interest in<br />
obtaining structural information for these molecules.<br />
In this contribution, recent results obtained in the Molecular Dynamics & Clusters laboratory at<br />
IESL are presented. Using a molecular beam apparatus equipped with a time–<strong>of</strong>-flight massspectrometer,<br />
charged clusters are produced in an ion-source which is based on the combination<br />
<strong>of</strong> laser ablation and supersonic gas-expansion.<br />
Mass-spectroscopy, phot<strong>of</strong>ragmentation spectroscopy <strong>of</strong> mass-selected ions and molecular<br />
beam scattering techniques with the aid <strong>of</strong> theoretical models are employed in order to infer the<br />
stability and the structure <strong>of</strong> these molecules.<br />
99
Metals<br />
101
A - 0<br />
102
Size, charge, and isomer specific vibrational spectroscopy <strong>of</strong> isolated<br />
metal clusters<br />
André Fielicke 1 , Christian Ratsch 1,2 , Gert von Helden 1 , and Gerard Meijer 1<br />
1 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195 Berlin, Germany<br />
2 Department <strong>of</strong> Mathematics, UCLA, Los Angeles, CA 90095-1555, USA<br />
A - 1<br />
We report on the vibrational spectra <strong>of</strong> neutral and charged metal clusters in the far infrared.<br />
These spectra are obtained via far infrared resonance enhanced multiple photon dissociation<br />
(FIR-MPD) <strong>of</strong> the complexes <strong>of</strong> metal clusters with rare gas atoms. The experiments make use<br />
<strong>of</strong> the Free Electron Laser for Infrared eXperiments FELIX in Nieuwegein, The Netherlands, as<br />
an intense and widely tunable far-infrared radiation source.<br />
The measured FIR-MPD spectra <strong>of</strong> the complexes represent the infrared absorption spectra <strong>of</strong><br />
the bare metal clusters. These spectra are unique for each cluster size and are true fingerprints <strong>of</strong><br />
the cluster’s structure. This FIR-MPD technique has been applied to cationic vanadium clusters<br />
[1] and cationic and neutral niobium clusters containing 3 to more than 20 atoms. Interestingly,<br />
for some cluster sizes, the vibrational spectra <strong>of</strong> neutral and cationic niobium clusters differ<br />
rather strongly, indicating different geometric structures. For smaller sized clusters (n
A - 2<br />
104<br />
Gold Clusters with Density-Functional Based Tight-Binding Method<br />
Pekka Koskinen 1 , Hannu Häkkinen 1 , Gotthard Seifert 2 , and Michael Moseler 3<br />
1 Department <strong>of</strong> Physics, NanoScience Center, 40014 University <strong>of</strong> Jyväskylä, Finland<br />
2 Institut für Physikalische Chemie, TU Dresden, Mommsenstrasse. 13, 01062 Dresden, Germany<br />
3 Fraunh<strong>of</strong>er Institut für Werkst<strong>of</strong>fmechanik, Wöhlerstrasse 11, 79108 Freiburg, Germany<br />
In this work we employ the density-functional based tight-binding method (DFTB)[1] in the<br />
study <strong>of</strong> structures and energies <strong>of</strong> neutral and charged gold clusters. These clusters have been<br />
studied extensively with the density-functional approach (DFT), but for clusters <strong>of</strong> larger size or<br />
for molecular dynamics simulations <strong>of</strong> more complex structures one should have a more<br />
efficient yet accurate computational tool. In this work we demonstrate that this efficient method<br />
might indeed be a useful tool in the study <strong>of</strong> gold clusters.<br />
As an example, Fig. 1 shows the reproducibility <strong>of</strong> the relative energies <strong>of</strong> the isomers <strong>of</strong> Au - 7clusters,<br />
as compared with previous DFT studies [2]. Even better than the energy, the method<br />
gives mainly the same stable cluster geometries as density-functional calculations. The<br />
electronic structure is well described, as can be seen in the vertical detachment energies in Fig 2.<br />
The DFTB-method is able to show that the structure <strong>of</strong> the ground state <strong>of</strong> small gold anions<br />
transforms from two-dimensional to three-dimensional at approximately correct cluster size. We<br />
studied larger Au - 55-cluster isomers and found the same stable structures compared to previous<br />
studies, as well as reasonable isomer energies [3].<br />
Fig.1 Energies and structures <strong>of</strong> a few Au - 7-clusters.<br />
The energies are calculated with self-consistent<br />
charge (SCC) DFTB as well as with DFT and plotted<br />
relative to the corresponding ground state.<br />
References<br />
Fig. 2 The vertical detachment energies <strong>of</strong> the Au - 7clusters<br />
shown. The values are consistently lower<br />
than gradient-corrected DFT (GGA), and the error is<br />
<strong>of</strong> the same order than with local-density DFT<br />
(LDA).<br />
[1] M. Elstner, D. Porezag, G. Jungnickel, J. Elstner, M Haug, Th. Frauenheim, S. Suhai, and G.<br />
Seifert, Phys. Rev. B 58, 7260 (1998).<br />
[2] H. Häkkinen, M. Moseler, and U. Landman, Phys. Rev. Lett. 89, 033401 (2002).<br />
[3] H. Häkkinen, M. Moseler, O. Kostko, N. Morgner, M.A. H<strong>of</strong>fmann, and B.v.Issendorff, Phys. Rev.<br />
Lett. 93, 093401 (2004)
A - 3<br />
Structure, energetics, and thermodynamics <strong>of</strong> copper, nickel, and gold<br />
clusters: N = 2–150<br />
V. G. Grigoryan, D. Alamanova, and M. Springborg<br />
<strong>Universität</strong> des Saarlandes, Physikalische und Theoretische Chemie, Postfach 151150<br />
D-66041 Saarbrücken, Germany<br />
The three most stable structures <strong>of</strong> CuN, NiN, and AuN clusters with N between 2 and 150<br />
have been determined using a combination <strong>of</strong> the Embedded-Atom (EAM), the quasi-Newton,<br />
and our own [1-3] Aufbau/Abbau methods for calculations <strong>of</strong> the total energies, local and global<br />
minima, accordingly. We have employed two well-known versions <strong>of</strong> the EAM: (1) the bulk<br />
version <strong>of</strong> Daw, Baskes and Foiles and (2) the Voter-Chen version which takes into account<br />
properties <strong>of</strong> the dimer. The lower-energy structures (also for the smallest ones) <strong>of</strong> CuN and NiN<br />
clusters (structural details, symmetry and the ordering <strong>of</strong> the isomers) obtained with the two<br />
versions are almost the same. Thus our study points to the universality <strong>of</strong> the bulk embedding<br />
functions and potentials for copper and nickel at least for computations <strong>of</strong> structural properties.<br />
But the bulk EAM fails completely to describe the structures <strong>of</strong> the smallest Au clusters. Hence<br />
for the gold clusters only the Voter-Chen version <strong>of</strong> the EAM has been used. Copper and nickel<br />
grow qualitatively similarly. Generally, we find a multilayered icosahedral or layer-by-layer<br />
growth. But the cluster growth pattern between two closed-shell icosahedra is not simple. It is<br />
predominantly icosahedral with islands <strong>of</strong> fcc, tetrahedral, and decahedral growth. Further, we<br />
have observed an enhanced ability <strong>of</strong> fcc clusters to compete with icosahedral and decahedral<br />
structures in the vicinity <strong>of</strong> N=79. The truncated centered octahedron at N=79 is the first and the<br />
second lower-energy structures for Cu and Ni clusters, respectively. The derived results are<br />
detailed discussed and compared with those <strong>of</strong> available ab initio and semiempirical studies.<br />
Agreement with experimental studies is very good in many cases. The situation for gold is more<br />
complicated. We could not detect any favored structural motif. For example, Au13 is the first<br />
Mackay icosahedron, Au38 is the truncated octahedron, but all the three isomers for Au55 are<br />
low-symmetric. Our result for 38-atom gold cluster agrees with the many-body Sutton-Chen and<br />
Murrell-Mottram calculations, but it is in contradiction with the 'disordered' result <strong>of</strong> the n-body<br />
Gupta potential. Hence more studies are needed. Furthermore, we determine the full vibrational<br />
spectrum and the vibrational heat capacities (contributions from rotations are negligible) <strong>of</strong><br />
clusters for each cluster size. It is found, that the 23-atom Cu or Ni cluster (triple icosahedron)<br />
possesses the highest vibrational frequency. Further it is shown that the highest vibrational<br />
frequency is lower in the fcc and decahedral clusters and higher in the icosahedral ones. The<br />
heat-capacity plots for low temperatures show very interesting fine structures with minima at<br />
magic numbers <strong>of</strong> 13 and 55 and with a broad maximum in the vicinity <strong>of</strong> N=35.<br />
References<br />
[1] V. G. Grigoryan and M. Springborg, Phys. Chem. Chem. Phys. 3, 5125 (2001).<br />
[2] V. G. Grigoryan and M. Springborg, Chem. Phys. Lett. 375, 219 (2003).<br />
[3] V. G. Grigoryan and M. Springborg, Phys. Rev. B 70, 205415 (2004).<br />
105
A - 4<br />
Structure Determination <strong>of</strong> Small Silver Cluster Ions by Trapped Ion<br />
Electron Diffraction<br />
106<br />
Detlef Schooss 1 , Martine N. Blom 1 , Lars Walter 1 , Mattias Kordel 1 , Jason Stairs 1 , Joel H. Parks 2 and<br />
Manfred M. Kappes 1,3<br />
1 Institute <strong>of</strong> Nanotechnology, Forschungszentrum Karlsruhe,D-76021 Karlsruhe, Germany<br />
2 The Rowland Institute at Harvard, Cambridge, MA 02142, USA<br />
3 Institut für Physikalische Chemie, <strong>Universität</strong> Karlsruhe, D-76128 Karlsruhe, Germany<br />
The structure <strong>of</strong> silver clusters ions is studied by the recently developed technique <strong>of</strong><br />
trapped ion electron diffraction (TIED) [1]. In brief, cluster ions are generated by a magnetron<br />
sputter source [2] and injected into a Paul ion trap. After mass selection and thermalization the<br />
trapped ions are irradiated with a 40 keV electron beam and the resulting diffraction pattern is<br />
integrated with a CCD detector. The sensitivity and resolution <strong>of</strong> the apparatus is documented<br />
by figure 1 which shows the molecular scattering function obtained for Ag55 + at 90K.<br />
+<br />
Figure 1: Experimental diffraction pattern (open squares) <strong>of</strong> mass selected Ag55 at 90K. The measurement is<br />
consistent with an icosahedral structure as calculated from RIDFT calculations (line).<br />
Comparison to RIDFT structure calculations for various trial geometries reveals that the cluster<br />
ensemble which was probed comprises predominantly icosahedral Ag55 + . TIED measurements<br />
at different cluster sizes and charge states (Ag19 +/- to Ag79 +/- ) at a variety <strong>of</strong> temperatures ranging<br />
from 100 - 650 K are presently ongoing.<br />
References<br />
[1] M. Maier-Borst, D. C. Cameron, M. Rokni and J. H. Parks, Phys. Rev. A, 59, R3162 (1998), S.<br />
Krückeberg, D. Schooss, M. Maier-Borst, J. H. Parks, Phys. Rev. Lett. 85(21), 4494-4497 (2000)<br />
[2] H. Haberland, M. Mall, M. Moseler, Y. Qiang, T. Reiners and Y. Thurner, J. Vac, Sci. Technol.<br />
A 12(5), 2925 (1994)
Metal Cluster Anions Produced by Attachment <strong>of</strong> Slow Electrons:<br />
Readjustment and Blurring <strong>of</strong> the Magic Numbers<br />
R. Rabinovitch, R. Moro, C. Xia, V. V. Kresin<br />
Dept. <strong>of</strong> Physics, University <strong>of</strong> Southern California, Los Angeles, California 90089-0484, USA<br />
A - 5<br />
The high electric polarizabilities <strong>of</strong> metal clusters enable them to attach low-energy<br />
electrons with very large cross sections [1]: a passing electron is captured by a strong longrange<br />
polarization potential. But very little is understood about the last stage <strong>of</strong> the collision<br />
process: where and how fast is the captured electron’s energy deposited? The questions are<br />
closely related to the general problem <strong>of</strong> electron relaxation in size-quantized nanoscale<br />
systems.<br />
To explore this issue, we are carrying out measurements <strong>of</strong> the mass spectra <strong>of</strong> negative sodium<br />
cluster ions born in the electron-cluster interaction region. If the energy deposited by the<br />
captured electron is quickly thermalized and is sufficient to cause rapid cluster evaporation,<br />
there should result - a rearrangement <strong>of</strong> the cluster abundances and a shift <strong>of</strong> the magic numbers<br />
Na<br />
from Nan to n-1 .<br />
In our experiment such a shift is clearly observed at shell closings near n=20 and n=40.<br />
However, near n=58 and n=92 the shell closings become completely blurred (see Figure 1). This<br />
interesting change may be due to a bottleneck in the electron relaxation and/or to insufficiently<br />
fast evaporation. We will present the current data and discuss their implications.<br />
This work was supported by the U. S. National Science Foundation.<br />
Counts<br />
500<br />
450<br />
400<br />
350<br />
300<br />
250<br />
200<br />
150<br />
100<br />
References<br />
Masscan <strong>of</strong> clusters Na18-Na21<br />
Sm oothing<br />
50<br />
380 400 420 440 460 480 500<br />
Mass, AMU<br />
-<br />
Counts<br />
350<br />
300<br />
250<br />
200<br />
150<br />
100<br />
Masscan <strong>of</strong> clusters Na56-Na59<br />
Sm oothing<br />
1260 1280 1300 1320 1340 1360 1380<br />
Mass, AMU<br />
Figure 1. Mass spectra <strong>of</strong> Na (left) and Na (right) formed by electron attachment.<br />
18-21<br />
56-59<br />
The shell edge is visible only in the first spectrum.<br />
[1] V.Kasperovich, G.Tikhonov, K.Wong, and V.V.Kresin, Phys. Rev. A 62, 063201 (2000); Phys.<br />
Rev. Lett. 85, 2729 (2000).<br />
-<br />
107
A - 6<br />
108<br />
Mass Spectrometric Investigations <strong>of</strong> Binary Clusters:<br />
Evidence for Endohedral Clusters with Enhanced Stability<br />
Peter Lievens, Ewald Janssens, Sven Neukermans, Xin Wang, Nele Veldeman, Roger E. Silverans<br />
Laboratorium voor Vaste-St<strong>of</strong>fysica en Magnetisme, K.U.Leuven,<br />
Celestijnenlaan 200D, B-3001 Leuven, Belgium<br />
While clusters composed <strong>of</strong> rare gas atoms exhibit enhanced stabilities when they have<br />
magic numbers enabling them to adopt high symmetry geometries ("shells <strong>of</strong> atoms"), the magic<br />
numbers in alkali and other simple metal clusters are determined by the number <strong>of</strong> delocalized<br />
valence electrons occupying a one-particle state in a (centro-)symmetric potential well ("shells<br />
<strong>of</strong> electrons"). The quest for such electronically and geometrically closed shells, which goes<br />
along with enhanced cluster stability, has been a leading thread in cluster research for many<br />
years. One route has been the investigation <strong>of</strong> binary clusters, which allows tailoring both the<br />
cluster geometry (number <strong>of</strong> atoms) and electronic properties (number <strong>of</strong> delocalized electrons)<br />
independently.<br />
We produce beams <strong>of</strong> binary clusters with a dual-target dual-laser vaporization cluster source,<br />
and investigate the clusters in the gas phase with mass spectrometric and laser spectroscopic<br />
techniques. In particular, size and composition dependent stability fluctuations are investigated<br />
with phot<strong>of</strong>ragmentation and mass spectrometry, and size dependent ionization energies are<br />
measured with threshold laser ionization spectroscopy.<br />
Lately we focussed on investigations <strong>of</strong> two types <strong>of</strong> bimetallic systems: clusters consisting <strong>of</strong><br />
noble metals doped with transition metal atoms, and clusters <strong>of</strong> group IVa elements doped with<br />
metal atoms [1-3]. In this contribution we will present evidence for the existence <strong>of</strong> combined<br />
closures <strong>of</strong> shells <strong>of</strong> atoms and shells <strong>of</strong> electrons for specific binary cluster species.<br />
Phenomenological interpretations <strong>of</strong> new electronic shell closures enhanced by size specific<br />
geometry considerations will be given based on comparisons with density functional theory<br />
calculations. In particular the formation <strong>of</strong> stable icosahedral 13 atom systems with the dopant<br />
atom occupying a central position will be highlighted. Also, size dependent magnetic properties<br />
<strong>of</strong> endohedral clusters with a magnetic atom occupying a central position will be discussed.<br />
This work was supported by the Fund for Scientific Research – Flanders (FWO), the Flemish<br />
Concerted Action (GOA) program, and the Belgian Interuniversity Poles <strong>of</strong> Attraction (IAP)<br />
program. EJ and SN are Postdoctoral Researchers <strong>of</strong> the FWO.<br />
References<br />
[1] S. Neukermans, E. Janssens, H. Tanaka, R.E. Silverans, P. Lievens, Phys. Rev. Lett. 90 (2003)<br />
#033401.<br />
[2] E. Janssens, H. Tanaka, S. Neukermans, R.E. Silverans, P. Lievens, New J. Phys. 5 (2003) #46.<br />
[3] S. Neukermans, E. Janssens, Z. Chen, R.E. Silverans, P.v.R. Schleyer, P. Lievens, Phys. Rev. Lett.<br />
92 (2004) #163401.
Photoelectron spectrometry <strong>of</strong> big sodium clusters<br />
Oleg Kostko and Bernd von Issendorff<br />
Fakultät für Physik, <strong>Universität</strong> Freiburg, H.Herderstr. 3, 79104 Freiburg, Germany<br />
A - 7<br />
We have measured photoelectron spectra (PES) <strong>of</strong> Na – n clusters with n=5-4000 at a photon<br />
energy <strong>of</strong> 4.02 eV. For the smaller sizes (n=5-480) a liquid nitrogen cooled rf-octupole trap was<br />
used for thermalization and intensity bunching. Bigger clusters were examined without<br />
additional thermalization. The estimated temperature <strong>of</strong> the clusters in both cases was about<br />
100 K. Comparison <strong>of</strong> the PES obtained this work with data published earlier [1,2] shows that<br />
the lower temperature leads to significantly better spectral resolution and in some cases to a<br />
change <strong>of</strong> the shape <strong>of</strong> the spectra.<br />
In the PES <strong>of</strong> the bigger clusters a periodic vanishing and appearing <strong>of</strong> structure was observed.<br />
For instance Na – 730 and Na – 1250 exhibit almost unstructured spectra, while Na – 670 and Na – 1350<br />
exhibit rather structured spectra. The reason for this behaviour seems to be a combination <strong>of</strong><br />
geometrical shell closing and electronic supershell modulation.<br />
From the measured photoelectron spectra the electron affinities <strong>of</strong> the anions and the ionization<br />
potentials <strong>of</strong> the neutrals were extracted. These values are plotted in Fig.1 as a function <strong>of</strong> N -1/3 .<br />
Their difference yields the cluster charging energy, which can be used to determine the Wigner-<br />
Seitz radius <strong>of</strong> sodium (Rws) and the electron spillout (δ). In our case values <strong>of</strong> 2.07 Å and<br />
0.97 Å were obtained, respectively. The literature value for Rws <strong>of</strong> bulk sodium at 100 K is<br />
2.08 Å. Fitting the electron affinity and ionization potential curves according to the charged<br />
droplet model<br />
2<br />
e<br />
IP = WF + α 1/<br />
3<br />
R N + δ<br />
additionally yields the parameter α=0.377 and the work function WF=2.84 eV, which is slightly<br />
higher then the literature value <strong>of</strong> 2.75 eV.<br />
EA and IP, eV<br />
4<br />
3<br />
2<br />
1<br />
IP<br />
EA<br />
0.0 0.1 0.2 0.3<br />
N<br />
0.4 0.5 0.6<br />
-1/3<br />
Figure 1. Electron affinity and ionization potential as a function <strong>of</strong> the inverse <strong>of</strong> the cubic root <strong>of</strong> the cluster size.<br />
References<br />
2,84 eV<br />
α=0.377<br />
δ=0.974Å<br />
R =2.072Å<br />
ws<br />
[1] G.Wrigge, M.Astruc H<strong>of</strong>fmann and B.v.Issendorff, Phys. Rev. A 65, 063201 (2002).<br />
[2] M.Moseler, B.Huber, H.Häkkinen, U.Landman, G.Wrigge, M.Astruc H<strong>of</strong>fmann and<br />
B.v.Issendorff, Phys. Rev. B 68, 165413 (2003).<br />
WS<br />
109
A - 8<br />
110<br />
Probing the properties <strong>of</strong> polyanionic clusters in a Penning trap<br />
Alexander Herlert 1,2 , Andreas Lassesson 1 , Franklin Martinez 1 , Gerrit Marx 1 ,<br />
Lutz Schweikhard 1 , Noelle Walsh 1<br />
1 Institut für Physik, Ernst-Moritz-Arndt-<strong>Universität</strong> Greifswald, 17487 Greifswald, Germany<br />
2 CERN, Department <strong>of</strong> Physics, 1211 Geneva 23, Switzerland<br />
Highly negatively charged clusters have attracted much interest within the last ten years [1]<br />
and their study has led to the development <strong>of</strong> a new field in cluster research. The addition <strong>of</strong><br />
further electrons to an already negatively charged system is in itself an experimental challenge,<br />
especially with respect to the stability <strong>of</strong> the polyanionic products. Furthermore, the additional<br />
negative charges may lead to a change in the dissociation processes after excitation <strong>of</strong> the highly<br />
charged clusters.<br />
With the application <strong>of</strong> a Penning trap for the simultaneous storage <strong>of</strong> low-energy electrons and<br />
singly-charged metal-cluster anions, the production <strong>of</strong> polyanionic metal clusters is reproducible<br />
under controlled conditions [2]. Size-selected metal cluster dianions as well as trianions are<br />
readily available for further investigation. First experiments concentrated on the relative yield <strong>of</strong><br />
the polyanionic metal clusters as a function <strong>of</strong> cluster size. The results are related to the second<br />
electron affinity <strong>of</strong> the clusters including electronic shell effects [3].<br />
Further investigations involved the excitation <strong>of</strong> the metal cluster dianions with photons and<br />
also by collisions with inert gas atoms. Both methods were already established at the<br />
ClusterTrap experiment [4]. In the case <strong>of</strong> collisional activation, the dianions are brought to a<br />
larger cyclotron radius to increase their kinetic energy. After the collision with argon gas atoms<br />
the emission <strong>of</strong> the surplus electron from the cluster was observed, but the change <strong>of</strong> the massover-charge<br />
ratio led to a change <strong>of</strong> the ion motion and thus to the loss <strong>of</strong> the product ions [5].<br />
For photoexcitation, the dianions were centered in the Penning trap and electron emission as<br />
well as dissociation was observed in case <strong>of</strong> gold-cluster dianions [6]. The data is currently<br />
being analyzed with respect to direct and thermionic electron emission.<br />
In addition to the experiments on polyanionic metal clusters, the investigation <strong>of</strong> highly charged<br />
fullerene anions has started. A new ion source for the ClusterTrap experiment has been<br />
constructed that allows the production <strong>of</strong> both positively and negatively charged fullerenes.<br />
Attachment <strong>of</strong> additional electrons to the singly charged fullerene anions has been successful<br />
and dianions Cn 2- in the size range n ≥ 70 were observed. First results <strong>of</strong> the production and<br />
further investigation <strong>of</strong> the size- and charge-state selected fullerene dianions will be presented.<br />
References<br />
[1] A. Dreuw and L.S. Cederbaum, Chem. Rev. 102, 181 (2002).<br />
[2] A. Herlert and L. Schweikhard, Int. J. Mass Spectrom. 229, 19 (2003).<br />
[3] C. Yannouleas et al., Phys. Rev. Lett. 86, 2996 (2001).<br />
[4] L. Schweikhard et al., Eur. Phys. J. D 24, 137 (2003).<br />
[5] A. Herlert and L. Schweikhard, Int. J. Mass Spectrom. 234, 161 (2004).<br />
[6] L. Schweikhard et al., Int. J. Mass Spectrom. 219, 363 (2002).
Geometric and electronic tructure <strong>of</strong> large sodium cluster anions<br />
Michael Moseler 1,2 , Bernd Huber 2 ,B. von Issendorff 3<br />
1 Fraunh<strong>of</strong>er Institut für Werkst<strong>of</strong>fmechanik, Wöhlerstrasse 11, 79108 Freiburg, Germany<br />
2 Freiburger Materialforschungszentrum , Stefan-Meier-Strasse 21, 79104 Freiburg, Germany<br />
3 Fakultät für Physik, <strong>Universität</strong> Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg, Germany<br />
A - 9<br />
Photoelectron spectroscopy is a frequently used experimental method to extract electronic<br />
binding energies from atomic, molecular, and condensed-matter systems. For molecules and<br />
clusters at low temperature, a comparison <strong>of</strong> the measured photoelectron spectra (PES) with the<br />
electronic density <strong>of</strong> states (DOS) obtained from density functional calculations for T=0 optimal<br />
structures, provides information about the underlying electronic structure and may lead to<br />
assignments <strong>of</strong> pertinent structures.<br />
For the range <strong>of</strong> N=4-19 the PES <strong>of</strong> NaN - clusters were compared with the DOS recorded in our<br />
finite-temperature ab initio simulations [1]. Although the main features <strong>of</strong> the PES can be<br />
understood through the use <strong>of</strong> the jellium model, we are able to detect and explain several<br />
spectral details caused by the finite temperature dynamics. Meanwhile experimental spectra<br />
from very cold cluster beams are available and a comparison with T=0 static spectra reveals<br />
new information concerning the ground states <strong>of</strong> the clusters.<br />
Also larger sodium cluster anions have been measured and simulated by us. For Na55 -, Na147 -<br />
and Na309 - the DOS <strong>of</strong> Mackay-icosahedral clusters was in good agreement with the<br />
corresponding PES (see Fig. 1) and for Na71 - a clear difference between the DOS <strong>of</strong> an anti-<br />
Mackay and an Mackay over layer has been detected.<br />
References<br />
Figure 1. Comparision <strong>of</strong> the Na309 - PES and the DOS <strong>of</strong> the Mackay-icosahedron.<br />
[1] M. Moseler, B. Huber, H. Häkkinen, U. Landman, G. Wrigge, M. Astruc H<strong>of</strong>fmann and B. von<br />
Issendorff, Phys. Rev. B 68, 165413 (2003).<br />
111
A - 10<br />
112<br />
Planar Boron Clusters and 2D to 3D Transitions<br />
Hua-Jin Zhai, 1,2 A. N. Alexandrova, 3 B. Kiran, 1,2 S. Bulusu, 4 Jun Li, 2 Xiao Cheng Zeng, 3<br />
A. I. Boldyrev, 3 and Lai-Sheng Wang 1<br />
1 Department <strong>of</strong> Physics, Washington State University, 2710 University Drive, Richland, WA 99352, USA<br />
and<br />
2 W. R. Wiley Environmental Molecular Sciences Laboratory andChemical Science Division, Pacific<br />
Northwest National Laboratory, P.O. Box 999, Richland, WA 99352, USA.<br />
3 Department <strong>of</strong> Chemistry and Biochemistry, Utah State University, Logan, Utah 84322-0300, USA<br />
4 Department <strong>of</strong> Chemistry and Center for Materials Research and Analysis, University <strong>of</strong> Nebraska-<br />
Lincoln, Lincoln, NE 68588, USA.<br />
One <strong>of</strong> the most interesting features <strong>of</strong> elemental boron and many bimetallic boron<br />
compounds is the occurrence <strong>of</strong> highly symmetric icosahedral clusters. The rich chemistry <strong>of</strong><br />
boron is also dominated by three-dimensional (3D) cage structures. We report our recent<br />
investigations <strong>of</strong> small boron clusters in the size range from 3 to 20 atoms using photoelectron<br />
spectroscopy and ab initio calculations [1-8]. We will present experimental and theoretical<br />
evidence that small boron clusters prefer planar structures and exhibit aromaticity and<br />
antiaromaticity according to the Hückel rules, akin to planar hydrocarbons up to the size <strong>of</strong> 19<br />
atoms. Aromatic boron clusters possess more circular shapes whereas antiaromatic boron<br />
clusters are elongated, analogous to structural distortions <strong>of</strong> antiaromatic hydrocarbons. In a<br />
very recent study [8], we show that 3D structures begin at B20, which has a double ring global<br />
minimum structure. The 2D to 3D structural transition observed at B20 suggests that it may be<br />
considered as the embryo <strong>of</strong> the thinnest single-wall boron nanotubes.<br />
References<br />
B12 B13 B20<br />
[1] H. J. Zhai, L. S. Wang, A. N. Alexandrova, and A. I. Boldyrev, J. Chem. Phys. 117, 7917-7924<br />
(2002).<br />
[2] A. N. Alexandrova, A. I. Boldyrev, H. J. Zhai, L. S. Wang, E. Steiner, and P. W. Fowler, J. Phys.<br />
Chem. A 107, 1359-1369 (2003).<br />
[3] H. J. Zhai, A. N. Alexandrova, K. A. Birch, A. I. Boldyrev, and L. S. Wang, Angew. Chem. Int. Ed.<br />
42, 6004-6008 (2003).<br />
[4] H. J. Zhai, B. Kiran, J. Li, and L. S. Wang, Nature Materials 2, 827-833 (2003).<br />
[5] H. J. Zhai, L. S. Wang, A. N. Alexandrova, A. I. Boldyrev, and V. G. Zakrzewski, J. Phys. Chem.<br />
A 107, 9319-9328 (2003)<br />
[6] A. N. Alexandrova, A. I Boldyrev, H. J. Zhai, and L. S. Wang, J. Phys. Chem. A 108, 3509-3517<br />
(2004).<br />
[7] “Boron Flat Out” (S. K. Ritter), Chem. & Eng. News 82 (9), 28-32 (March 1 (2004).<br />
[8] B. Kiran, S. Bulusu, H. J. Zhai, S. Yoo, X. C. Zeng, and L. S. Wang, Proc. Natl. Acad. Sci. (USA),<br />
in press.
Molecular Clusters<br />
113
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114
Molecular Beams <strong>of</strong> Organic Molecules<br />
Tim Krause, Adnan Sarfraz, Wolfgang Christen<br />
Institut für Chemie, Humboldt-<strong>Universität</strong> zu Berlin, 12489 Berlin, Germany<br />
A - 11<br />
The transfer <strong>of</strong> non-volatile or thermally unstable molecules into the gas phase is <strong>of</strong> utmost<br />
importance for a variety <strong>of</strong> applications such as analytical mass spectrometry, optical spectroscopy,<br />
or the epitaxial growth <strong>of</strong> thin films. One possible method is the expansion <strong>of</strong> supercritical<br />
solutions into a molecular beam. Here the key idea is to dissolve the substance at high<br />
pressure, exploiting the supercritical fluid's solvent power, and precipitate it by expansion.<br />
Extending our previous work on caffeine [1] and small molecules (vitamin K3, phenylalanine<br />
tertbutylester) [2] we report the successful expansion <strong>of</strong> several molecules <strong>of</strong> biological interest<br />
in supercritical CO2 at temperatures <strong>of</strong> only 310-315 K, and accompanying detection using mass<br />
spectrometry.<br />
References<br />
[1] W. Christen, S. Geggier, S. Grigorenko, K. Rademann, Rev. Sci. Instrum. 75, 5048 (2004).<br />
[2] W. Christen, T. Krause, H. Noack, A. Sarfraz, J. Chem. Phys., to be submitted.<br />
115
A - 12<br />
116<br />
Infrared Spectroscopy <strong>of</strong> CO2 Containing Cluster Anions<br />
Holger Schneider 1 , A. Daniel Boese 2 1, *<br />
, J. Mathias Weber<br />
1 Institut für Physikalische Chemie, <strong>Universität</strong> Karlsruhe, Kaiserstr. 12, 76229 Karlsruhe, Germany<br />
* email: jmathias.weber@chemie.uni-karlsruhe.de<br />
2 Institut für Nanotechnologie, Forschungszentrum Karlsruhe, Pstfach 3640, 76021 Karlsruhe, Germany<br />
Molecular clusters are relevant model systems for the study <strong>of</strong> intermolecular interaction<br />
potentials governing the structures <strong>of</strong> molecular complexes. Structural information on clusters<br />
can be gained from infrared photodissociation spectroscopy in molecular beams [1, 2], and we<br />
have applied this technique to several species, probing the interaction <strong>of</strong> various anions with<br />
CO2. The experimental results are interpreted in the framework <strong>of</strong> density functional theory with<br />
anharmonic calculations <strong>of</strong> vibrational spectra.<br />
Halide-CO2 complexes afford the study <strong>of</strong> the interaction <strong>of</strong> CO2 with closed shell anions <strong>of</strong> low<br />
reactivity [3]. The results are compared with those for Au - ·CO2 [4], which is relevant for the<br />
study <strong>of</strong> catalytic oxidation <strong>of</strong> CO by gold clusters on surfaces [5, 6]. This complex shows<br />
strong interaction between CO2 and the Au - anion, with a strongly deformed CO2 unit.<br />
Complexes <strong>of</strong> O2 - with CO2 show very interesting motifs <strong>of</strong> ion solvation [7]. The π* orbital <strong>of</strong><br />
O2 - <strong>of</strong>fers a template with four a priori equivalent binding sites for the structure <strong>of</strong> the<br />
microsolvation environment. However, only one CO2 ligand is strongly bound, with additional<br />
molecules weakly attached to the resulting CO4 - anion.<br />
The general motif <strong>of</strong> anions binding to CO2 is binding to CO2 via the carbon atom, in contrast to<br />
cations, which generally dock to one <strong>of</strong> the oxygen atoms. The geometry <strong>of</strong> the CO2 molecule is<br />
changed upon complexation with the anion by electrostatic and charge transfer effects. Both<br />
contributions deform the molecule away from the linear configuration <strong>of</strong> neutral CO2 towards<br />
the bent anionic shape.<br />
References<br />
[1] W.H. Robertson and M.A. Johnson, Annu. Rev. Phys. Chem. 54 (2003) 173.<br />
[2] M.A. Duncan, Int. Rev. Phys. Chem. 22 (2003) 407.<br />
[3] J.M. Weber and H. Schneider, J. Chem. Phys. 120 (2004) 10056.<br />
[4] A.D. Boese, H. Schneider, A.N. Gloess, and J.M. Weber, in preparation (2004).<br />
[5] A. Sanchez, et al., J. Phys. Chem. A 103 (1999) 9573.<br />
[6] L.D. Socaciu, et al., J. Am. Chem. Soc. 125 (2003) 10437.<br />
[7] H. Schneider, A.D. Boese, and J.M. Weber, in preparation (2004).
Infrared Spectroscopy <strong>of</strong> XY - ·(C2H2)n Cluster Ions (XY = O2, C2H)<br />
Holger Schneider, J. Mathias Weber *<br />
Institut für Physikalische Chemie, <strong>Universität</strong> Karlsruhe, Kaiserstr. 12, 76229 Karlsruhe, Germany<br />
* corresponding author; email: jmathias.weber@chemie.uni-karlsruhe.de<br />
A - 13<br />
Proton or hydrogen transfer is an important process in chemistry. The intermolecular<br />
interaction potentials governing reactive processes can be studied by vibrational spectroscopy <strong>of</strong><br />
complexes containing the reactants.[1, 2] We report the infrared photodissociation spectra <strong>of</strong><br />
ion-acetylene clusters, with O2 - and C2H - as proton acceptors. The experimental results are<br />
interpreted in the framework <strong>of</strong> density functional theory.<br />
Complexes <strong>of</strong> strong ionic proton acceptors with acetylene molecules can be studied as models<br />
for proton acceptors [3]. All studied complexes are formed by C2H2 molecules docking to the<br />
ions by forming an H-bond. In the case <strong>of</strong> superoxide, each ligand binds to a lobe <strong>of</strong> the π*<br />
orbital <strong>of</strong> O2 - , affording a similar binding motif for all acetylene molecules. In contrast, HC2 - has<br />
only one ionic binding site, and the one <strong>of</strong> the ligands is favoured, while all others are less<br />
strongly bound.<br />
References<br />
[1] W.H. Robertson and M.A. Johnson, Annu. Rev. Phys. Chem. 54 (2003) 173.<br />
[2] M.A. Duncan, Int. Rev. Phys. Chem. 22 (2003) 407.<br />
[3] P. Botschwina, et al., Faraday Discuss. 118 (2001) 433.<br />
117
A - 14<br />
118<br />
Computational Study <strong>of</strong> (H2S) 2≤ n ≤ 10 Clusters<br />
Mehmet Bahat and Ziya Kantarci<br />
Gazi University, Physics Department, 06500, Teknikokullar, Ankara, Turkey.<br />
Molecular clusters are the subject <strong>of</strong> continuing investigations both experimentally and<br />
theoretically in recent years. One <strong>of</strong> them water clusters have been the subject <strong>of</strong> significant<br />
research activity. However, little information for the H2S clusters is available from theoretical<br />
and experimental point <strong>of</strong> view at present. Most calculations have focused on the dimer<br />
structure. Experimentally photoionization studies for the H2S clusters through heptamer have<br />
been studied.<br />
We have studied structures,energies and vibrational spectra <strong>of</strong> (H2S) 2≤ n ≤ 6 clusters<br />
computationally, will be send elsewhere.<br />
In this study, we will present structure, energy, polarizability and hyperpolarizability properties<br />
<strong>of</strong> (H2S) 2≤ n ≤ 10 clusters which calculated using B3LYP/cc-pVTZ level <strong>of</strong> theory.
Structural and spectral features <strong>of</strong> size selected water clusters in the<br />
n=7-21 regime: Results from electronic structure calculations and<br />
empirical potentials<br />
A - 15<br />
George S Fanourgakis 1 , Anita Lagutschenkov 2 , Gereon Niedner-Schatteburg 2 and Sotiris S. Xantheas 1<br />
1 Chemical Sciences Division, Pacific Northwest National Laboratory, 902 Battelle Boulevard, PO Box<br />
999, MS K1-83, Richland, WA 99352, USA<br />
2 Department <strong>of</strong> Chemistry, Chemie, University <strong>of</strong> Kaiserslautern, Erwin Schroedinger Strasse, 67663<br />
Kaiserslautern, Germany<br />
The structural patterns adopted by the clusters <strong>of</strong> the first few molecules <strong>of</strong> water are<br />
determined from the maximization <strong>of</strong> hydrogen bonding, the minimization <strong>of</strong> dangling bonds<br />
and the formation <strong>of</strong> local networks, which exhibit large cooperative effects. To this end, the<br />
global minima <strong>of</strong> the first few water clusters are characterized by structures in which all<br />
molecules are on the surface <strong>of</strong> the cluster. The structural transition between “all-surface” and<br />
“internally solvated” water cluster structures is investigated using high-level ab-initio electronic<br />
structure methods and the results are compared to the ones with empirical potentials. An<br />
informative probing <strong>of</strong> these hydrogen bonding networks is achieved by infrared (IR)<br />
spectroscopy in the 3000 – 4000 cm -1 range, a part <strong>of</strong> the spectra that corresponds to the<br />
“fingerprint” <strong>of</strong> the underlying network and its connectivity. We present the spectral features<br />
that are associated with the structural transition from “all-surface” to “internally solvated”<br />
structures in water clusters. We furthermore rely on the use <strong>of</strong> Schlegel diagrams in order to<br />
identify the most intense, red-shifted OH stretching vibrations which are used in order to probe<br />
the underlying hydrogen bonding network.<br />
119
Phase Transitions<br />
121
A - 15<br />
122
Structural changes in small and medium-size rare-gas cluster cations.<br />
Aleš Vítek, František Karlický, and René Kalus<br />
Department <strong>of</strong> Physics, University <strong>of</strong> Ostrava,30. dubna 22, 701 03 Ostrava, Czech Republic<br />
A - 16<br />
Constant-energy and constant-temperature Monte Carlo simulations have been performed to<br />
localize temperature-dependent structural changes in selected krypton cluster cations, Kr3 + , Kr4 + ,<br />
and Kr12-14 + . The trimer and tetramer cations are used to analyze possible structural changes in<br />
the ionic cores <strong>of</strong> larger KrN + clusters, the Kr12-14 + cations are included as representatives <strong>of</strong><br />
these larger clusters to assess the role <strong>of</strong> solvation effects and to study the phase changes<br />
occurring in neutral solvation shells. The intra-cluster interactions <strong>of</strong> KrN + are described by<br />
means <strong>of</strong> previously developed models based on the diatomics-in-molecules approach with the<br />
inclusion <strong>of</strong> the spin-orbit coupling and the most important three-body polarization interactions.<br />
123
A - 17<br />
124<br />
Experimental study <strong>of</strong> the phase transformations<br />
in molecular clusters <strong>of</strong> Ar and N2<br />
O. G. Danylchenko, S. I. Kovalenko, V. N. Samovarov<br />
B. Verkin Institute for Low Temperature Physics and Engineering, Natl. Academy <strong>of</strong> Sciences <strong>of</strong> Ukraine,<br />
47 Lenin Ave., Kharkov, 61103, Ukraine<br />
We use an electron diffraction technique to study the structure <strong>of</strong> substrate-free Ar and N2<br />
clusters and nanoparticles formed in the process <strong>of</strong> homogeneous nucleation in a supersonic jet<br />
isentropically expanding into vacuum. The average size N <strong>of</strong> aggregations varied between 5⋅10 2<br />
and 1.5⋅10 5 atoms (molecules) per cluster. The temperature <strong>of</strong> clusters and nanoparticles was<br />
T=(38±5) K in the diffraction zone.<br />
Analysis <strong>of</strong> the obtained electron-diffraction patterns has shown for the first time the existence<br />
<strong>of</strong> an amorphous phase in large rare-gas clusters (N≈600 atoms/cluster). As N increased in a<br />
relatively narrow size interval a transition occurred from the amorphous phase to the multilayer<br />
icosahedral one observed for N=1300 atoms/cluster. Formation <strong>of</strong> a crystalline face-centered<br />
cubic (fcc) structure <strong>of</strong> argon with stacking faults took place for N=3⋅10 3 atoms/cluster which is<br />
in good accordance with the previous observations [1,2]. The electron-diffraction patterns <strong>of</strong><br />
bigger clusters (N∼10 4 atoms/cluster) are shown to be characterized by hexagonal close-packed<br />
(hcp) maxima along with the fcc peaks. The intensity <strong>of</strong> the hcp peaks grew with increasing<br />
aggregation size, and for nanoparticles with N∼10 5 atoms/cluster we clearly detected (100),<br />
(101), (103), and (202) peaks characteristic <strong>of</strong> an hcp structure with intensity comparable with<br />
that <strong>of</strong> the fcc peaks.<br />
In case <strong>of</strong> linear molecules like those <strong>of</strong> nitrogen, besides the central interaction between<br />
particles there is a considerable contribution <strong>of</strong> non-central electrostatic forces which are<br />
responsible for the orientational ordering <strong>of</strong> molecules at low temperatures. The structure <strong>of</strong><br />
such clusters can differ significantly from the structure <strong>of</strong> rare-gas clusters depending on the<br />
anisotropic contribution to the total lattice energy. In contrast to amorphous argon clusters, for<br />
nitrogen beams with N≈500 molecules/cluster we first observed the formation <strong>of</strong> aggregations<br />
with multilayer icosahedral packing <strong>of</strong> molecules. The ‘wings’ <strong>of</strong> the most prominent<br />
icosahedral-phase maximum (in the region corresponding to the (100) and (101) peaks <strong>of</strong> the<br />
high-temperature β phase <strong>of</strong> N2, α-β phase transition in a bulk at T=35.6 K) are found to be<br />
curved thus indicating the presence <strong>of</strong> traces <strong>of</strong> the β phase in these clusters. As the cluster size<br />
grows at the same T in the diffraction zone, the diffraction pattern undergoes transformations<br />
and for N∼10 3 molecules/cluster it contains maxima <strong>of</strong> both cubic (α) and hcp (β) phases.<br />
Further cluster growing is accompanied by a decrease in the intensity <strong>of</strong> the cubic-phase peaks<br />
and strenghening <strong>of</strong> the hcp peaks. Clusters with N∼10 4 actually have only the high-temperature<br />
β phase.<br />
We propose and discuss a mechanism underlying the observed structural transformations in Ar<br />
and N2 which supposes cluster formation from a liquid droplet and takes into account the<br />
kinetics <strong>of</strong> phase growth when there are energy barriers between phases.<br />
References<br />
[1] I. Farges, M.F. de Feraudy, B. Roult, G. Torchet, Adv. Chem. Phys. 70, 45 (1988).<br />
[2] O.G. Danylchenko, S.I. Kovalenko, V.N. Samovarov, Low Temp. Phys. 30, 166 (2004).
Molecular Dynamics Simulations <strong>of</strong> the Melting-like Transition in<br />
Homogeneous and Heterogeneous Alkali Clusters<br />
Andrés Aguado and José M. López<br />
A - 18<br />
Department <strong>of</strong> Theoretical Physics, University <strong>of</strong> Valladolid, C/ Real de Burgos s/n, Valladolid, 47011,<br />
Spain<br />
A theoretical analysis <strong>of</strong> the equilibrium geometries and thermal behaviour <strong>of</strong> the impuritydoped<br />
A1Na54 (with A=Li,K,Rb,Cs) clusters, <strong>of</strong> binary Li13Na42 and Na13Cs42 and <strong>of</strong> ternary<br />
Li13Na32Cs12 nanoalloys is presented. The calculations are based on the orbital-free approach to<br />
density functional theory and the classical newtonian equations to deal with the electronic and<br />
ionic subsystems, respectively. The icosahedral symmetry <strong>of</strong> homogeneous Na55 is preserved in<br />
the impurity-doped clusters, with the Li impurity located at the center <strong>of</strong> the icosahedron and<br />
K,Rb and Cs impurities occupying a surface site. The ground state<br />
isomer <strong>of</strong> Na13Cs42 and Li13Na32Cs12 nanoalloys is an onion-like polyicosahedral structure, with<br />
a core shell formed by the element <strong>of</strong> highest surface tension and smallest atomic size, and a<br />
surface shell formed by the atomic species <strong>of</strong> largest size and lowest surface tension. Li13Na42<br />
adopts an amorphous-like structure, albeit with significant polyicosahedral local order, due to<br />
partial mixing <strong>of</strong> Li and Na species in the core-shell. Regarding the thermal properties, the<br />
impurity-doped clusters A1Na54 are found to melt in two well-defined steps upon heating, each<br />
one associated to the activation <strong>of</strong> diffusive motion for atoms <strong>of</strong> a given species. Regarding the<br />
thermal behavior <strong>of</strong> nanoalloys, we have not studied yet explicitly a representative number <strong>of</strong><br />
examples and can not draw very general conclusions. However, our partial results already<br />
indicate that: (1) when the polyicosahedral ordering is not perfect and/or the structure is not<br />
highly compact (as is the case for Li13Na42 and Na13Cs42), premelting effects are more relevant<br />
than in corresponding homogeneous clusters; (2) if<br />
polyicosahedral ordering is strictly preserved (as it<br />
happens for Li13Na32Cs12) the relative stability <strong>of</strong> the<br />
solid-like phase can be significantly enhanced. For<br />
example, the surface <strong>of</strong> this ternary cluster (formed by<br />
Cs atoms) melts at approximately 140 K, which is 50<br />
K above typical surface melting temperatures <strong>of</strong><br />
homogeneous Cs clusters.<br />
If possible, we will complement the results mentioned<br />
in the previous paragraph with those <strong>of</strong> additional<br />
molecular dynamics simulations on homogeneous and<br />
heterogeneous alkali clusters which are still on the<br />
way at the date <strong>of</strong> submission <strong>of</strong> this abstract.<br />
References<br />
Figure 1. Ground state structure <strong>of</strong> Li 13Na 30Cs 12.<br />
[1] A. Aguado, L. E. González, and J. M. López, J. Phys. Chem. B 108, 11722 (2004).<br />
[2] A. Aguado, J. M. López, and S. Núñez, Comp. Mat. Sci. to be published.<br />
[3] A. Aguado and J. M. López, unpublished works.<br />
125
A - 19<br />
126<br />
Phase Changes in Clusters: Targets for Experiments<br />
R. Stephen Berry 1 , and Ana Proykova 2<br />
1 Department <strong>of</strong> Chemistry and The James Franck Institute, The University <strong>of</strong> Chicago, Chicago,<br />
Illinois 60637, USA<br />
2 University <strong>of</strong> S<strong>of</strong>ia, Faculty <strong>of</strong> Physics, 5 James Bourchier Blvd, S<strong>of</strong>ia 1126, Bulgaria<br />
It is now well established that some clusters exhibit the finite-system counterparts <strong>of</strong> firstorder<br />
transitions, and that these differ from bulk phase transitions ins<strong>of</strong>ar as clusters may exist<br />
in two or more phases in observable amounts, in thermal equilibrium. It is also apparent from<br />
simulations that bulk second-order transitions may have small-system analogues that have either<br />
one or two local free-energy minima, corresponding to second-order-like or first-order-like<br />
behavior. These findings raise several questions that await experimental study. One is the<br />
observation <strong>of</strong> sharp upper or (more likely) lower temperature bounds for the local stability <strong>of</strong><br />
the unfavored phase. A second is the possibility <strong>of</strong> observing and distinguishing between cases<br />
in which phases persist long enough to exhibit well-defined, measurable characteristics and<br />
cases in which the dynamic equilibrium between the phases is so labile that no well-defined<br />
distinguishable phases can be observed. Still a third challenge is the possibility <strong>of</strong> observing<br />
phase changes or phase coexistence that look first-order-like in small clusters but become<br />
second-order in the large-system limit. With this challenge is the alternative <strong>of</strong> true secondorder-like<br />
behavior in which multiple phases do not coexist because the free energy has only a<br />
single minimum. All <strong>of</strong> these are experimental investigations that will almost certainly require<br />
monodisperse cluster samples, because the phase behavior <strong>of</strong> small clusters is highly variable<br />
and not at all monotonic with cluster size.
Rare Gases<br />
127
A - 19<br />
128
A - 20<br />
Decay behaviour <strong>of</strong> dimer ions: kinetic energy distributions and 1/t law<br />
J. Fedor 1 , K. Głuch 2 , S. Matt-Leubner 1 , O. Echt 3 , P. Scheier 1 , F. Hagelberg 4 , K. Hansen 5 , J. U. Andersen 6 ,<br />
T. D. Märk 1<br />
1 Institute for Ion Physics, Innsbruck University, Technikerstrasse 25, A-6020 Innsbruck, Austria<br />
2 Institute <strong>of</strong> Mathematics, Physics and Informatics, Maria Curie-Skłodowska University, Lublin 20-031,<br />
Poland<br />
3 Dept. <strong>of</strong> Physics, University <strong>of</strong> New Hampshire, Durham, NH 03824, USA<br />
4 Dept. <strong>of</strong> Physics, Atmospheric Sciences, and General Science, Jackson State University, Jackson, MS<br />
39217, USA<br />
5 Department <strong>of</strong> Physics, Gothenburg University, SE-41296 Gothenburg, Sweden<br />
6 Institute <strong>of</strong> Physics and Astronomy, University <strong>of</strong> Aarhus, DK-8000 Aarhus, Denmark.<br />
There exists a plethora <strong>of</strong> data on metastable decay <strong>of</strong> large cluster ions. For instance, the<br />
analysis <strong>of</strong> the kinetic energy distributions <strong>of</strong> fragment ions has led to the evaluation <strong>of</strong> their<br />
binding energies [1] and the time dependence <strong>of</strong> the decay intensity has been shown to obey a<br />
powerlaw [2]. These decays have been successfully described with statistical theories.<br />
Dimers represent the system where the degree <strong>of</strong> randomization required for thermal statistical<br />
treatment is not possible. Experimental findings on dimer ions however show that they can have<br />
decay characteristics resembling those <strong>of</strong> the large clusters.<br />
Here we present the measurements <strong>of</strong> the kinetic energy release distributions <strong>of</strong> the rare gas<br />
dimer anions (Ne2 + , Ar2 + , Kr2 + , Xe2 + ) using a three sector field mass spectrometer, as well as the<br />
measurements <strong>of</strong> decay intensity time dependence for the dissociation <strong>of</strong> the metal dimer anions<br />
(Cu2 - , Ag2 - ) obtained on the ELISA storage ring in Aarhus. The decay behaviour has been<br />
successfully explained either by the metastable electronic transitions in case <strong>of</strong> rare gases or by<br />
the tunneling through the high angular momentum barrier in the metal anions. The quasicontinuum<br />
<strong>of</strong> rotational states in the later case is sufficiently dense to lead to a 1/t law.<br />
References<br />
[1] K. Gluch, S. Matt-Leubner, O. Echt, R. Deng, J.U. Andersen, P. Scheier and T.D. Märk, Chem.<br />
Phys. Lett. 385 449 (2004)<br />
[2] K.Hansen, J.U.Andersen, P.Hvelplund, S.P.Møller, U.V.Pedersen and V.V.Petrunin,<br />
Phys.Rev.Lett. 87 123401 (2001)<br />
129
A - 21<br />
130<br />
Fragmentation dynamics <strong>of</strong> rare-gas trimer cations.<br />
Ivan Janeček, Daniel Hrivňák, and René Kalus<br />
Department <strong>of</strong> Physics, University <strong>of</strong> Ostrava,30. dubna 22, 701 03 Ostrava, Czech Republic<br />
Hemiquantal, mean-field dynamics and recently developed extended diatomics-inmolecules<br />
models <strong>of</strong> intra-cluster interactions with the inclusion <strong>of</strong> the spin-orbit coupling and<br />
the most important three-body forces are used to study fragmentation <strong>of</strong> argon, krypton and<br />
xenon trimer cations after a sudden ionization <strong>of</strong> respective vibrationally excited neutral trimers.<br />
Both fragmentation from adiabatic and diabatic states is included and the computational results<br />
are compared, where possible, with data from experiments as well as from other theoretical<br />
studies. The main focus is on the role the spin-orbit coupling plays in the relaxation <strong>of</strong> the initial<br />
electronic excitation and during its conversion into cluster vibrational energy. Kinetics <strong>of</strong> the<br />
cluster fragmentation is thoroughly analyzed and recognized to consist <strong>of</strong> two (or even more)<br />
consecutive first-order processes most probably involving the electronic relaxation and the<br />
subsequent cluster decay.
High resolution electron ionization study <strong>of</strong> helium-clusters<br />
S. Denifl 1 , S. Ptasińska 1 , F. Martinez 2 , K. Głuch 3 , S. Feil 1 , P. Scheier 1 , T. D. Märk 1<br />
A - 22<br />
1 Insitut für Ionenphysi,, <strong>Universität</strong> Innsbruck, Technikerstrasse 25, 6020 Innsbruck, Austria<br />
2 Institut für Physik, Ernst Moritz Arndt <strong>Universität</strong> Greifswald, Domstrasse 10a,17487 Greifswald,<br />
Germany<br />
3 Institute <strong>of</strong> Physics, Maria Curie-Sklodowska University, Pl. Marii Curie-Sklodowskiej 1, 20-031 Lublin,<br />
Poland<br />
After many years <strong>of</strong> research the determination and interpretation <strong>of</strong> appearance energies<br />
(AE’s) for clusters using electron impact ionization is still difficult and involves large error bars.<br />
The reasons for this are a number <strong>of</strong> technical obstacles to prepare electrons with high-energy<br />
resolution. In addition we are confronted with a complicated physical situation <strong>of</strong> a reaction<br />
complex involving a quantum mechanical many body system. The use <strong>of</strong> photoionization<br />
sometimes appears to be less difficult but nevertheless the AE values obtained are not directly<br />
comparable to those obtained by electron impact studies. Both processes are intrinsically<br />
different, because the transition complexes in the ionization process are not the same.<br />
This work presents the high resolution study <strong>of</strong> the threshold behavior for small helium cluster<br />
ions. The crossed electron/cluster beams apparatus used for these measurements consists <strong>of</strong> a<br />
cluster source, a hemispherical electron monochromator and a quadrupole mass spectrometer. A<br />
standard home-built hemispherical electron analyzer produces electrons with a typical energy<br />
distribution <strong>of</strong> 150 meV. The helium clusters are produced by supersonic expansion in a cluster<br />
source which can be cooled down to 8.5 K. Previously already all other rare gases (Ne, Ar, Kr,<br />
Xe), H2-, D2-, N2- and N2O-clusters have been studied with the present experimental setup<br />
(except a different cluster source was used). The data evaluation is basing on an extension <strong>of</strong><br />
Wannier’s law for the ionization <strong>of</strong> atoms towards the case <strong>of</strong> clusters. The present results for<br />
helium cluster up to size n = 10 are compared with those <strong>of</strong> previous experiments with small<br />
helium clusters using electron impact [1] or photon impact [2], respectively.<br />
This work was supported by FWF, Wien, Austria, and the European Commission,<br />
Brussels.<br />
References<br />
[1] R. Fröchtenicht, U. Henne, J. P. Toennis, A. Ding, M. Fieber-Erdmann, T. Drewello, J. Chem.<br />
Phys. 104, 2548 (1996).<br />
[2] B. E. Callicoat, K. Förde, L. F. Jung, T. Ruchti, K. C. Janda, J. Chem. Phys. 109, 10195 (1998).<br />
131
A - 23<br />
132<br />
Surface Entropy <strong>of</strong> Argon Clusters<br />
Mikael Kjellberg, Sergey Prasalovich, Vladimir Popok, Klavs Hansen, Eleanor E. B. Campbell<br />
Department <strong>of</strong> Physics, Göteborg University, SE-41296 Göteborg, Sweden<br />
The enhanced stability <strong>of</strong> certain cluster sizes is traditionally inferred from the enhanced<br />
abundance <strong>of</strong> these species in mass spectra. For rare gas clusters, the stability pattern can be<br />
described as due to a close packing <strong>of</strong> atoms into closed structures (shells) with the symmetry <strong>of</strong><br />
Mackay icosahedra. The mere presence <strong>of</strong> shell closings does not give any information on the<br />
magnitude <strong>of</strong> the energies involved. A quantitative comparison requires knowledge <strong>of</strong> the<br />
binding energies <strong>of</strong> the clusters. It is possible to extract this information from the mass spectra<br />
by making reasonable general assumptions [1] with the restriction that only relative values can<br />
be found. The flat abundance spectrum (after background subtraction) is related to relative<br />
I ∝ D + C D − D G.<br />
energies as ( )<br />
N N+ 1 v N N+<br />
1 /<br />
This has been done in Fig 1(A) for masses around the N = 55 “magic number”. The amplitude<br />
in the relative energy variations does not follow the same trend as the local abundance<br />
variations. In particular the maximum in the relative energy is shifted to smaller N. The reason<br />
for this is that the relative energies obtained in this procedure are not the dissociation energies,<br />
DN, <strong>of</strong> the clusters but the free energies, FN = DN – TSN, where SN is identified with the surface<br />
entropy (the natural logarithm <strong>of</strong> the number <strong>of</strong> ways the configurational ground state can be<br />
contructed). This can be estimated from the structures calculated by Northby [2] and used to<br />
extract the dissociation energies. This is shown in Fig. 1(B) and compared with the calculated<br />
dissociation energies, where the absolute scale was obtained by scaling with the bulk and<br />
surface energy. The agreement <strong>of</strong> the trend in the values is very satisfactory.<br />
∆F (meV)<br />
80<br />
75<br />
70<br />
65<br />
60<br />
Figure 1. A, Left:Integrated peak intensities from Ar N + mass spectrum filled squares, (right y-axis) and the<br />
dissociation energies extracted from the spectrum (free energies) (open squares, left y-axis). B, Right: Extracted<br />
dissociation energies (free energies) (open circles), dissociation energies after subtraction <strong>of</strong> the entropy term (open<br />
squares), calculated energies from Northby [2] (filled squares).<br />
References<br />
50 51 52 53 54 55 56 57 58 59 60<br />
0<br />
61<br />
N<br />
[1] K. Hansen and U. Näher, Phys. Rev. A , 60 1240 (1999).<br />
[2] J.A. Northby, J. Xie, D.L. Freeman, J.D. Doll, Z. Phys. D 12 69 (1989)<br />
∆F<br />
I N<br />
3<br />
2<br />
1<br />
I N<br />
Energies [meV]<br />
85<br />
80<br />
75<br />
70<br />
65<br />
60<br />
55<br />
50<br />
45<br />
∆F N,exp<br />
D N,exp<br />
D N,Northby<br />
50 52 54 56 58 60<br />
N
Photodissociation <strong>of</strong> rare-gas trimer cations.<br />
Daniel Hrivňák 1 , René Kalus 1 , Florent X. Gadéa 2<br />
1 Department <strong>of</strong> Physics, University <strong>of</strong> Ostrava, Czech Republic<br />
2 Groupe NanoScience, CEMES, France<br />
A - 24<br />
Hemiquantal, mean-field dynamics and recently developed extended diatomics-inmolecules<br />
models <strong>of</strong> intra-cluster interactions and electronic transitions in rare-gas cluster<br />
cations are used to study the dissociation <strong>of</strong> argon, krypton and xenon trimer cations after<br />
absorption <strong>of</strong> a photon. The main focus is on the importance <strong>of</strong> the spin-orbit coupling for the<br />
photodissociation dynamics. The theoretical data on fragmentation channels, the kinetic energy<br />
<strong>of</strong> phot<strong>of</strong>ragments and the ratios for the symmetric and asymmetric fragmentation are<br />
thoroughly compared with the experimental data by Haberland’s group. A very good agreement<br />
is obtained. The importance <strong>of</strong> initial vibrational excitations <strong>of</strong> the trimer cations is also<br />
analyzed using a constant-temperature Monte Carlo sampling method. It has been found that the<br />
kinetic energy <strong>of</strong> phot<strong>of</strong>ragments is only negligibly influenced by the initial heating <strong>of</strong> the<br />
trimer, the ratios <strong>of</strong> the symmetric fragmentation change significantly with temperature<br />
however, particularly in the temperature region corresponding to structural changes <strong>of</strong> the<br />
trimers.<br />
133
Semiconductors<br />
135
A - 24<br />
136
A - 25<br />
Theoretical Investigation <strong>of</strong> the Influence <strong>of</strong> Ligands on Structural and<br />
Electronic Properties <strong>of</strong> Indium Phosphide Clusters<br />
Sudip Roy, Michael Springborg<br />
Physikalische Chemie, <strong>Universität</strong> des Saarlandes, 66123 Saarbrücken, Germany<br />
Results <strong>of</strong> a theoretical study <strong>of</strong> the effects <strong>of</strong> including ligands on stoichiometric InnPn<br />
clusters are presented. We apply a parameterized density-functional method 1 and consider<br />
clusters with n up to above 70. As ligands we consider H atoms and CH3 groups, and the results<br />
are compared with our earlier ones for the naked clusters 2 . We find that the ligands lead to only<br />
smaller structural changes, but that an enhanced In-to-P electron transfer in the outermost parts<br />
<strong>of</strong> the clusters, that we observed for the naked clusters, is largely suppressed, so that there is a<br />
more homogeneous In-to-P transfer throughout the whole cluster. Adding the ligands leads in<br />
most cases to an increase in the HOMO-LUMO gap and, therefore, also to an increase in the<br />
stability <strong>of</strong> the clusters. However, we find also that the HOMO-LUMO gap depends critically<br />
on the type, sites, and number <strong>of</strong> the ligands that are added.<br />
References<br />
[1] G. Seifert, D. Porezag, and Th. Frauenheim, Int. J. Quant. Chem., 58, 185 (1996).<br />
[2] S. Roy and M. Springborg, J. Phys. Chem. B , 107, 2771 (2003)<br />
137
A - 26<br />
138<br />
Sizedependence <strong>of</strong> Electronic and Structural Properties <strong>of</strong><br />
Semiconductor Nanoparticles<br />
Michael Springborg, Jan-Ole Joswig, Sudip Roy, Pranab Sarkar<br />
Physical and Theoretical Chemistry, University <strong>of</strong> Saarland, 66123 Saarbrücken, Germany<br />
Using a parameterized density-functional method we have calculated the electronic and<br />
structural properties <strong>of</strong> naked AB semiconductor nanoparticles as a function <strong>of</strong> size with up to<br />
around 200 atoms. We assumed that the structure is related to that <strong>of</strong> a spherical cutout <strong>of</strong> either<br />
the zincblende or the wurtzite crystal structure, which subsequently is allowed to relax to its<br />
closest total-energy minimum. In addition, we have also studied core/shell nanoparticles where<br />
one semiconductor forms the shell on the core <strong>of</strong> another semiconductor. The properties that we<br />
shall discuss include structure, optical gap, charge transfers and stability.
Structural, Electronic and Optical Properties <strong>of</strong><br />
Surface saturated Cadmium Sulfide Clusters<br />
Johannes Frenzel 1 , Gotthard Seifert 1 , Jan-Ole Joswig 2 , Michael Springborg 2<br />
1 Institut für Physikalische Chemie, Technische <strong>Universität</strong> Dresden, D-01062 Dresden, Germany<br />
2 Institut für Physikalische Chemie, <strong>Universität</strong> des Saarlandes, D-66123 Saarbrücken, Germany<br />
A - 27<br />
Due to the quantum-confinement effects the optical properties <strong>of</strong> cadmium sulfide clusters<br />
tune with respect to their size. In this theoretical work clusters up to 4 nm in diameter, derived<br />
from the electronically almost degenerated crystal structures <strong>of</strong> cadmium sulfide, wurtzite and<br />
zinc blende (sphalerite), were studied systematically using a simplified LCAO-DFT-LDA<br />
method (DFTB) 1,2 . With a time-dependent extension (TD-DFRT-TB) 2 <strong>of</strong> this method the optical<br />
spectra <strong>of</strong> bare and surface saturated cadmium sulfide clusters were calculated. Since there is a<br />
strong dependency <strong>of</strong> the lowest unoccupied molecular orbitals on structural properties,<br />
basically on the number single-bonded surface atoms the HOMO/LUMO gap trend to zero for<br />
clusters having a large number <strong>of</strong> single bonded Cadmium atoms 3 . It is shown that effect,<br />
caused by low lying cadmium 5s states, disappears when to these clusters surfactants are added,<br />
namely hydrogen atoms and thiol-groups and their spectra show an asymptotical decreasing <strong>of</strong><br />
the HOMO/LUMO gap toward the bulk band gap <strong>of</strong> CdS while increasing their size.<br />
Figure 1. Structurual shape (left side) and TD-DFRT-TB spectra (right side) <strong>of</strong> a spherical cadmium sulfide clusters,<br />
unsaturated (dashed curve) and saturated (solid curve).The curves are broadened with Gausians (0.1 eV).<br />
References<br />
[1] Porezag, D. et al., Phys. Rev. B 51, 12947 (1995).<br />
[2] Seifert, G. et al., Int. J. Quantum Chem. 58,185 (1996).<br />
[3] Niehaus, T. et al., Phys. Rev. B 63, 085108 (2001).<br />
[4] Joswig, J.-O. et al., J. Phys. Chem B 107, 2897 (2003).<br />
139
Solvations<br />
141
A - 27<br />
142
Ionization Potentials <strong>of</strong> Large Sodium Doped Ammonia Clusters<br />
Christ<strong>of</strong> Steinbach, Udo Buck<br />
Max-Planck-Institut für Strömungsforschung, Bunsenstrasse 10, 37073 Göttingen, Germany<br />
A - 28<br />
In a continuous neat supersonic expansion ammonia clusters are generated and doped with<br />
sodium atoms in a pickup cell. In this way Na(NH3)n clusters are produced and photoionized by<br />
a tunable dye laser system. The ions are mass analyzed in a reflectron time-<strong>of</strong>-flight mass<br />
spectrometer, and the wavelength dependent ion signals serve for the determination <strong>of</strong> the<br />
ionization potentials (IP) <strong>of</strong> the different clusters in the size range 10 < n < 500. For clusters n <<br />
18 the results agree with those published previously. 1 In particular, the plateau for 10 < n
A - 29<br />
Charge and Energy Transfer Processes Induced by Core Ionization <strong>of</strong><br />
Anion-Molecule Microsolvated Clusters<br />
144<br />
Nikolai V. Kryzhevoi, Lorenz S. Cederbaum<br />
Theoretical Chemistry, Institute <strong>of</strong> Physical Chemistry, Heidelberg University,<br />
Im Neuenheimer Feld 229, 69120 Heidelberg, Germany<br />
Cluster physics pertains to exploration <strong>of</strong> various active topics <strong>of</strong> chemical science.<br />
Solvation is among them. Studying microsolvated clusters provides an opportunity to gain<br />
insight into the solvation phenomenon at the microscopic level. Anion-molecule microsolvated<br />
clusters are <strong>of</strong> wide interest due to their unique properties. As well as being a subject <strong>of</strong> diverse<br />
experimental studies, small clusters are also amenable to accurate theoretical treatments from<br />
first principles. The first core level ab initio investigation <strong>of</strong> selected clusters <strong>of</strong> this type are<br />
reported here. The localized character <strong>of</strong> core electrons allows one to probe local properties <strong>of</strong><br />
selected units <strong>of</strong> clusters providing information on the chemical state and interactions <strong>of</strong> each<br />
unit with its local environment. Ionization <strong>of</strong> molecular core levels in anion-molecule clusters<br />
induces, besides local excitations in the molecule itself, a variety <strong>of</strong> charge and energy transfer<br />
processes which are nonlocal in nature. Low-lying satellites appearing in core level spectra due<br />
to these nonlocal processes are apparently not present in spectra <strong>of</strong> free molecules and are a<br />
peculiarity <strong>of</strong> clusters only. Energies and intensities <strong>of</strong> these satellites are found to strongly<br />
depend on the chemical type <strong>of</strong> the anion as well as on the type <strong>of</strong> the ionized solvent molecule.<br />
It is shown that valuable information on properties <strong>of</strong> anion-molecule clusters and their<br />
monomers like the strength <strong>of</strong> anion-molecule interaction and the geometry <strong>of</strong> the clusters can<br />
be obtain by studying charge and energy transfer satellites in core level spectra <strong>of</strong> clusters.
First principles studies on the reaction mechanisms for the intracluster<br />
reactions in Mg + (H2O)n and Al + (H2O)n<br />
Zhifeng Liu<br />
Department <strong>of</strong> Chemistry<br />
Chinese University <strong>of</strong> Hong Kong<br />
Shatin, Hong Kong, China<br />
A - 30<br />
Size dependent reactions in solvation clusters provide invaluable clues to the link<br />
between the microsolvation environment and the reaction mechanisms. The loss <strong>of</strong> a<br />
hydrogen atom in an Mg + (H2O)n and the loss <strong>of</strong> a hydrogen molecule in an Al + (H2O)n<br />
cluster are the classical examples <strong>of</strong> such reactions, which are turned on at a certain size<br />
(5 for Mg + (H2O)n and 12 for Al + (H2O)n) and then turned <strong>of</strong>f at a larger size (17 for<br />
Mg + (H2O)n and 24 for Al + (H2O)n). The properties and structures <strong>of</strong> these clusters have<br />
attracted much attention over the years. In this presentation, I will report the recent<br />
progresses made in my group to understand the mechanisms for these size dependent<br />
reactions by first principles calculations [1, 2, 3]. In the case <strong>of</strong> Al + (H2O)n, the reactivity<br />
is actually due to its isomer (HAlOH) + (H2O)n-1 and is controlled by the cage-like cluster<br />
structure, which is essential to bring a proton near the H--Al bond. In contrast, the<br />
crucial factor in the case <strong>of</strong> Mg + (H2O)n is the solvation <strong>of</strong> the unpaired electron, as the<br />
relative distance between the electron and the Mg 2+ center determines the barrier for the<br />
production <strong>of</strong> the H atom. The details for both clusters provide interesting examples on<br />
the subtle and intricate effects <strong>of</strong> solvation on chemical reactions.<br />
References:<br />
[1] C.K. Siu, Z.F. Liu, and J.S. Tse, “Ab Initio Studies on Al + (H2O)n, HAlOH + (H2O)n-1, and the Size<br />
Dependent H2 Elimination Reaction”, J. Am. Chem. Soc. 124 (2002) 10846-60<br />
[2] C.K. Siu, and Z.F. Liu, “Ab initio Studies on the Mechanism <strong>of</strong> the Size Dependent H Elimination<br />
Reaction in Mg + (H2O)n”, Chem. Eu. J. 8 (2002) 3177-86<br />
[3] C.K. Siu, and Z.F. Liu, “Reaction mechanisms for the size-dependent H loss in Mg + (H2O)n:<br />
solvation controlled electron transfer”, submitted to Phys. Chem. Chem. Phys.<br />
145
Surface<br />
147
148
Alkali Metal Atoms and Clusters on Graphite:<br />
a Density Functional Study<br />
K. Rytkönen 1 , J. Akola 2 , M. Manninen 1<br />
1 Nanoscience Center, P.O. Box 35, FIN-40014 University <strong>of</strong> Jyväskylä, Finland<br />
2 Institut fϋr Festkörperforschung, Forschungszentrum Jϋlich, D-52425 Jϋlich, Germany<br />
A - 31<br />
Sodium atoms and clusters (≤ 5) on graphite (0001) are studied using density functional<br />
theory, pseudopotentials and periodic boundary conditions [1]. A single Na atom is observed to<br />
bind at a hollow site 2.45 Å above the surface with an adsorption energy <strong>of</strong> 0.51 eV. The small<br />
diffusion barrier <strong>of</strong> 0.06 eV indicates a flat potential energy surface. Increased Na coverage<br />
results in a weak adsorbate-substrate interaction, which is evident in the larger separation from<br />
the surface in the cases <strong>of</strong> Na3, Na4, Na5, and the (2×2) Na overlayer. The binding is weak for<br />
Na2, which has a full valence electron shell. The presence <strong>of</strong> substrate modifies the structures <strong>of</strong><br />
Na3, Na4, and Na5 significantly, and both Na4 and Na5 are distorted from planarity. The<br />
calculated formation energies suggest that clustering <strong>of</strong> atoms is energetically favorable, and<br />
that the open shell clusters (e.g. Na3 and Na5) can be more abundant on graphite than in the gas<br />
phase. Analysis <strong>of</strong> the lateral charge density distributions <strong>of</strong> Na and Na3 shows a charge transfer<br />
<strong>of</strong> ~0.5 electrons in both cases. Results for other alkali metals (Li, K, Rb, Cs) will be presented<br />
too.<br />
References<br />
[1] K. Rytkönen, J. Akola, and M. Manninen, Phys. Rev. B 69, 205404 (2004).<br />
149
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150<br />
Single Atom Dispersion <strong>of</strong> Platinum on Carbon Nanotubes<br />
Yong-Tae Kim 1 , Kazuyoshi Ohshima 1 , Koichi Higashimine 2 , Kazuo Kato 3 , Tomoya Uruga 3 , Keiichi<br />
Osaka 3 , Kenichi Kato 3,4 , Masaki Takada 3,4 , Hiroyoshi Suematsu 3 , Tadaoki Mitani 1<br />
1 School <strong>of</strong> Materials Science and Center for Nano Materials and Technology, Japan Advanced<br />
2 Institute <strong>of</strong> Science and Technology (JAIST), 1-1 Asahidai, Tatsunokuchi, Ishikawa 923-1292, Japan<br />
3 Japan Synchrotron Radiation Research Institute (JASRI)/SPring-8, 1-1-1 Kouto, Mikazuki,<br />
Hyogo 679-5198, Japan<br />
4 Core Research for Evolutional Science and Technology, Japan Science Technology Cooperation<br />
(CREST/JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan<br />
Electrocatalyst is the key factor to determine the performance <strong>of</strong> fuel cell. Generally, it is<br />
prepared by the supporting electrocatalytical active material such as platinum on carbon<br />
materials in order to elevate an activity and reduce the usage <strong>of</strong> novel metal. Carbon supports<br />
therefore affect largely the properties <strong>of</strong> electrocatalyst such as dispersity, size distribution,<br />
particle shape and intrinsic conductivity. Since the discovery <strong>of</strong> carbon nanotubes (CNT) in<br />
1991 by Iijima 1 , the application to electrocatalyst supports has been attempted in order to utilize<br />
their superior properties such as good intrinsic conductivity, adequate specific surface area,<br />
accessible surface texture and electrochemical stability. However, there have been also a<br />
limitation that it is difficult to disperse highly and uniformly electrocatalytical active material on<br />
CNT, because they have the inert and plane surface which is difficult to wet in precursor<br />
solution and easy to cause the agglomeration 2 . In order to solve this problem, we adopted the<br />
introduction <strong>of</strong> thiol groups known to be the functional groups having a good affinity to novel<br />
metal on CNT surfaces. It was expected that high dispersity could be obtained by preventing the<br />
agglomeration among Pt clusters, since surface thiol groups formed the strong bonding with Pt<br />
clusters.<br />
Surprisingly, it was revealed that the surface <strong>of</strong> thiolated carbon nanotubes was covered with the<br />
mono-layer <strong>of</strong> single platinum atoms bonded with the surface thiol groups over our expectation.<br />
This phenomenon was confirmed with several analysis tools, such as X-ray Absorption Fine<br />
Structure analysis (EXAFS, XANES), X-Ray Diffractometry (XRD) with synchrotron radiation<br />
<strong>of</strong> SPring-8, X-ray Photoemission Spectrometry (XPS) and Transmission Electron Microscopy<br />
(TEM).<br />
Here we report the single atom dispersion as the extreme dispersed state <strong>of</strong> metal and the<br />
possibility to control the cluster size uniformly from single atom.<br />
References<br />
O<br />
Pt<br />
S<br />
NH<br />
C<br />
O<br />
Pt<br />
S<br />
NH<br />
C<br />
Figure 1. Schematic diagram <strong>of</strong> single Pt atom dispersion on CNT.<br />
[1] S. Iijima, Nature 354, 56 (1991).<br />
[2] E. Dujardin, T. W. Ebbesen, H. Hiura, K. Tanigaki, Science 265, 1850 (1994).<br />
O<br />
Pt<br />
S<br />
NH<br />
C<br />
O<br />
Pt<br />
S<br />
NH<br />
C<br />
O<br />
Pt<br />
S<br />
NH<br />
C
Self-Assembly <strong>of</strong> Metal Nanoclusters on Oxide Surfaces<br />
N. Berdunov 1 , G. Mariotto 1 , S. Murphy 1 , K. Balakrishnan 1 , Y. M. Mukovskii 2 , I. V. Shvets 1<br />
1 SFI Laboratories, Physics Dept., Trinity College Dublin, Ireland<br />
2 MISIS, Leninsky Prospect 4, Moscow 119991, Russia<br />
A - 33<br />
The self-assembly <strong>of</strong> ordered arrays <strong>of</strong> metal nanoclusters is a fascinating scientific<br />
phenomenon as well as a particularly promising subject for technological applications, such as<br />
microelectronics, ultra-high density recording, corrosion and catalysis. For example, magnetite<br />
and iron play an important role in industrial processes such as the production <strong>of</strong> hydrogen and<br />
the synthesis <strong>of</strong> ammonia. The ability <strong>of</strong> controlling the size and arrangement <strong>of</strong> Fe<br />
nanostructures may influence the way catalytic processes take place.<br />
We have studied the formation <strong>of</strong> Fe nanostructures on the magnetite (111) surface <strong>of</strong> single<br />
crystals and thin films. The Fe3O4(111) surface exhibits an hexagonal 42 Å superstructure, when<br />
annealed in oxygen atmosphere [1]. We have shown that this highly regular pattern is useful as<br />
a template for the self-assembly <strong>of</strong> nanostructures.<br />
We have deposited Fe films <strong>of</strong> 0.2, 0.5, 1 and 2 Å thickness at room temperature by means <strong>of</strong><br />
electron beam evaporation. STM images prove that ordered nucleation <strong>of</strong> nanoclusters takes<br />
place only on the patterned regions <strong>of</strong> the surface, while random nucleation takes place on the<br />
unpatterned regions (see Fig. 1). These results have been reproduced in the case <strong>of</strong> a 0.5 Å Cr<br />
film. The metal nanostructures are characterized by a very regular size distribution over a length<br />
<strong>of</strong> several hundreds nanometers.<br />
Our results demonstrate that the self-assembly <strong>of</strong> crystalline Fe and Cr nanostructures takes<br />
place on the preferential nucleation sites provided by the nanopatterned Fe3O4(111) surface. We<br />
suggest that ordered arrays <strong>of</strong> nanostructures could be grown on different oxides displaying<br />
long-range surface reconstruction, as recently demonstrated by the growth <strong>of</strong> ordered Pd<br />
clusters on Al2O3 [2].<br />
Figure 1. 80 nm × 80 nm STM image <strong>of</strong> 0.5 Å Fe deposited onto the Fe3O4(111) surface. Self-assembly <strong>of</strong> Fe<br />
nanostructures takes place only on the patterned areas <strong>of</strong> the crystal (terrace A), while Fe nucleates randomly onto the<br />
unpatterned areas (terrace B).<br />
References<br />
[1] N. Berdunov, S. Murphy, G. Mariotto and I.V. Shvets, Phys. Rev. B 70, 085404 (2004).<br />
[2] S. Degen, C. Becker and K. Wandelt, Faraday Discuss. 125, 343 (2004).<br />
151
A - 34<br />
152<br />
Supported Gold Clusters and Cluster-Based Nanoparticles:<br />
Characterization, Stability and Growth Studies by In Situ Grazing<br />
Incidence Small Angle X-ray Scattering Technique<br />
Stefan Vajda 1 , Jeffrey W. Elam 2 , Byeongdu Lee 3 , Michael J. Pellin 4 , Sönke Seifert 3 , George Y.<br />
Tikhonov 1 and Nancy A. Tomczyk 1 , Randall E. Winans 1,3<br />
1 Chemistry Division, 2 Energy Systems Division, 3 Experimental Facility Division, and 4 Materials Science<br />
Division<br />
Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 6043, USA<br />
Supported clusters possess unique, strongly size-dependent properties. However, the<br />
Achilles heal <strong>of</strong> supported particles remains their sintering at elevated temperatures or when<br />
exposed to mixtures <strong>of</strong> reactive gases. In this paper, the issue <strong>of</strong> thermal stability and<br />
agglomeration <strong>of</strong> atomic gold clusters and nanoparticles produced by cluster deposition on<br />
oxide surfaces is addressed as a function <strong>of</strong> deposited cluster size, level <strong>of</strong> surface coverage,<br />
temperature and time <strong>of</strong> heat treatment by synchrotron X-ray radiation at the Advanced Photon<br />
Source.<br />
The continuous beam <strong>of</strong> gold clusters was generated in a laser vaporization source. The Aun +<br />
clusters were deflected into setup with an incorporated mass spectrometer for the pre-selection<br />
<strong>of</strong> narrow cluster distributions in the size range Aun + , n=2,…10, with 1 to 5 dominant sizes. As<br />
support, silica as well as Al2O3 and TiO2 films grown by atomic layer deposition on<br />
SiO2/Si(111) were used. Coverages up to 45% <strong>of</strong> atomic monolayer equivalents were employed.<br />
The temperature region <strong>of</strong> aggregation was determined by gradually heating up the samples and<br />
recording 2-D X-ray scattering images during the heat treatment. The analysis <strong>of</strong> the data<br />
provides information about the average size and shape <strong>of</strong> supported particles [1].<br />
The size <strong>of</strong> the nanoparticles formed on the surface upon cluster deposition and their thermal<br />
stability exhibited a very strong dependence on the initial size <strong>of</strong> the clusters, level <strong>of</strong> surface<br />
coverage and material <strong>of</strong> the support. When applying surface coverages higher than 5% ML,<br />
aggregation <strong>of</strong> the clusters into nanometer-size particles with narrow size distribution prevailed.<br />
With decreasing coverage, the fraction <strong>of</strong> not-aggregated clusters significantly increased. Heat<br />
treatment led to final particle sizes determined by initial cluster size, coverage and length <strong>of</strong><br />
treatment. The most striking results were observed when depositing 2.5 % ML <strong>of</strong> Au7-Au10<br />
clusters on SiO2/Si(111): particles <strong>of</strong> one size, corresponding to Au20 were formed. Moreover,<br />
these particles exhibited extraordinary and unexpected thermal stability as well, not undergoing<br />
aggregation until 400 °C, when an onset <strong>of</strong> a slow agglomeration takes place [2]. Work on<br />
supported clusters <strong>of</strong> single size and in reactive gas atmosphere is currently under progress.<br />
This work and use <strong>of</strong> APS was supported by the U.S. Department <strong>of</strong> Energy, Office <strong>of</strong> Basic<br />
Energy Sciences, Division <strong>of</strong> Chemical Sciences, Geosciences, and Biosciences under contract<br />
number W-31-109-ENG-38.<br />
References<br />
[1] R. E. Winans, S. Vajda, B. Lee, S. J. Riley, S. Seifert, G.Y. Tikhonov, N. Tomczyk, J. Phys.<br />
Chem. B, 108, 18105 (2004).<br />
[2] S. Vajda, R. E. Winans, J.W. Elam, B. Lee, M.J. Pellin, S.J. Riley, S. Seifert, G.Y. Tikhonov and<br />
N. A. Tomczyk, invited paper, submitted to ACS.
Oxidation <strong>of</strong> free and supported Pd clusters<br />
Bernd Huber 1 , Michael Moseler 1,2<br />
1 Freiburger Materialforschungszentrum , Stefan-Meier-Strasse 21, 79104 Freiburg, Germany<br />
2 Fraunh<strong>of</strong>er Institut für Werkst<strong>of</strong>fmechanik, Wöhlerstrasse 11, 79108 Freiburg, Germany<br />
A - 35<br />
The adsorption sites <strong>of</strong> O2 on neutral PdN clusters (N=1-5) were studied using spin density<br />
functional theory [1]. Only for Pd1O2 molecular adsorption is found to be favorable. For Pd2-5O2<br />
dissociative adsorption with the oxygen sitting on Pd bridge sites is preferred. For N=4,5 the<br />
cluster increases its spin state from triplet to a quintet state in comparision to the pure gas phase<br />
Pd cluster. For molecular adsorption the O-O bond gets activated to a superoxolike state.<br />
While for the gas phase clusters the adsorption-induced relaxation <strong>of</strong> the PdN cluster was small,<br />
we see for the oxidation on MgO supported clusters the breaking <strong>of</strong> Pd-Pd bonds and the<br />
formation <strong>of</strong> nano-oxides reflecting the ionic crystal structure <strong>of</strong> the MgO underlayer (Fig. 1).<br />
Figure 1. The formation <strong>of</strong> Pd4 nano-oxides on a MgO underlayer. While the oxidized gas phase Pd 4 cluster (a)<br />
remains in the same structure as the pure cluster, supported Pd 4O 2 deforms into a structure reflecting the ionic crystal<br />
structure <strong>of</strong> the MgO underlayer (b + c).<br />
References<br />
[1] B. Huber, H. Häkkinen, U. Landman and M. Moseler, Comp. Mat. Sci. (accepted).<br />
153
A - 36<br />
The Size-Evolution <strong>of</strong> the Optical Properties <strong>of</strong> Supported Gold<br />
Clusters and Nanocrystals Studied by Cavity Ringdown Spectroscopy:<br />
From the Atom to the Bulk<br />
154<br />
J. M. Antonietti, M. Michalski, H. Jones, and U. Heiz<br />
Institute <strong>of</strong> Surface Chemistry and Catalysis, <strong>Universität</strong> Ulm, 89069 Ulm, Germany<br />
Measuring the size-dependent electronic structure <strong>of</strong> supported clusters near the Fermi level<br />
is <strong>of</strong> critical importance in order to understand the catalytic activities <strong>of</strong> supported clusters or to<br />
tune the optical properties <strong>of</strong> cluster assembled materials with the number <strong>of</strong> atoms. Up to now,<br />
extensive studies on the electronic structure <strong>of</strong> size-selected, supported clusters are sparse,<br />
because <strong>of</strong> the experimental challenges which must be overcome: preparation <strong>of</strong> monodispersed<br />
samples, high sensitivity required for recording the signal arising from a highly dilute sample,<br />
detection <strong>of</strong> the signal due to the clusters from the intense background signal arising from the<br />
substrate.<br />
In order to overcome these problems, a new experimental setup has been designed and built to<br />
perfom Cavity Ringdown Spectroscopy (CRDS) in the visible spectral range on size-selected<br />
clusters deposited on silica in UHV conditions. The clusters are produced in a laser vaporization<br />
source, size-selected in the gas phase, and s<strong>of</strong>t-landed onto the substrate.<br />
In this work, the ability to prepare monodispersed cluster samples is demonstrated. The ultimate<br />
sensitivity <strong>of</strong> the setup is such that absorption cross-sections <strong>of</strong> 0.02 Å 2 with cluster coverage<br />
down to 0.05% <strong>of</strong> a monolayer (~1 10 12 clusters/cm 2 ) can be detected. The absorption spectra <strong>of</strong><br />
gold clusters, Aun (n = 1, 4, 8, and 20) deposited on silica are presented. Additionally, the<br />
optical properties <strong>of</strong> self-organized gold nanocrystals with well-defined diameters (1 to 20 nm),<br />
prepared by chemical means and deposited on silica have been measured. The spectrum <strong>of</strong> the<br />
atom exhibits sharp peaks which are attributed to atoms attached at various defect sites on the<br />
surface. A dramatic size-sensitivity <strong>of</strong> the absorption properties <strong>of</strong> clusters is observed.<br />
However, Au8 shows features which are associated with nanocrystals, rather than small clusters.
A - 37<br />
The Influence <strong>of</strong> Growth Kinetics on Island Morphology for Antimony<br />
and Bismuth Diffusion and Aggregation on Graphite<br />
Bernhard Kaiser 1 , Bert Stegemann 1 , Shelley Scott 2;3 , Simon Brown 2;3<br />
1 Institute for Chemistry, Humboldt-University, Berlin, Germany<br />
2 The MacDiarmid Institute for Advanced Materials and Nanotechnology, New Zealand<br />
3 Department <strong>of</strong> Physics and Astronomy, University <strong>of</strong> Canterbury, Christchurch, New Zealand<br />
The morphology <strong>of</strong> antimony and bismuth islands has been studied with scanning electron<br />
microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy<br />
(AFM). Altering the deposition parameters (particle flux and coverage) shifts the balance<br />
between thermodynamics and kinetics. For antimony islands, we observe that for low flux and<br />
coverage the islands are compact, but undergo a transition to dendritic morphologies for higher<br />
flux and coverage regimes, consistent with previous investigations [1]. The islands also become<br />
flatter with increasing flux. For bismuth islands, we find a morphology transition from<br />
hexagonal to six-pointed star with increasing kinetic influence. Also, the island height is<br />
independent <strong>of</strong> flux, and vertical growth proceeds via an unusual striped layer growth.<br />
Furthermore, for bismuth it is possible to grow nanorods with a well-defined diameter <strong>of</strong> only a<br />
few nanometers and a length <strong>of</strong> several micrometers.<br />
References<br />
[1] B. Kaiser, B. Stegemann, H. Kaukel, K . Rademann, Surf. Sci. 496, L18 (2002)<br />
155
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156<br />
Transition From One- to Two-Dimensional Island Growth During<br />
Molecular Beam Epitaxy: A Monte Carlo Study<br />
S. P. Shrestha 1 and C. Y. Park 2<br />
1 Department <strong>of</strong> Physics, Patan M. Campus, Patan Dhola, Nepal<br />
2 Department <strong>of</strong> Physics, Sung Kyun Kwan University, Suwon 440-746, South Korea<br />
We present the Monte Carlo results for submonolayer island growth during Molecular<br />
Beam Epitaxy using irreversible nucleation and growth model. We have monitored island<br />
morphology and island anisotropy parameter for different diffusional and sticking anisotropy<br />
case. We find that in anisotropic sticking case, when diffusion is isotropic, increase in D/F leads<br />
highly elongated islands where as when diffusion is anisotropic, only slight elongation <strong>of</strong><br />
islands are observed. In this case, for all values <strong>of</strong> D/F ratio, increase in DA is observed to cause<br />
decrease in island elongation. Thus, when sticking is anisotropic, diffusional anisotropy<br />
produces adverse effect on island elongation. When sticking is isotropic islands always show 2d<br />
nature and when it is highly anisotropic the islands show 1d nature. At intermediate sticking<br />
ratio, the D/F ratio results in transition <strong>of</strong> island morphology from 1d nature at low D/F ratio to<br />
2d nature at high D/F ratio.
Spectroscopy <strong>of</strong> free clusters and clusters on surfaces<br />
Chunrong Yin 1 , I. Barke 2 , D. Böcker 2 , Th. Irawan 2 , H. Hövel 2 , and B. v. Issendorff 1<br />
1 Department <strong>of</strong> Physics, University <strong>of</strong> Freiburg, Stefan-Meier Str. 21, D-79104 Freiburg, Germany<br />
2 University <strong>of</strong> Dortmund, Experimentelle Physik I, D-44221 Dortmund, Germany<br />
A - 39<br />
Understanding the evolution <strong>of</strong> physical properties from free clusters to clusters on surfaces<br />
is a prerequisite for the use <strong>of</strong> clusters in technical applications. Photoelectron spectroscopy<br />
(PES) is a powerful tool to study the electronic properties <strong>of</strong> free clusters in vacuum as well as<br />
<strong>of</strong> supported clusters. Scanning tunneling spectroscopy (STS) is able to probe the electronic<br />
structure <strong>of</strong> individual clusters. Up to now, however, for metal clusters on surfaces these three<br />
techniques seemed to yield rather different results. A direct comparison <strong>of</strong> the results obtained<br />
on free clusters as well as on the same clusters deposited on well defined surfaces will hopefully<br />
clarify this situation, and yield definite informations about the electronic structure <strong>of</strong> the<br />
cluster/surface system and the nature <strong>of</strong> charge transfer processes between the cluster and the<br />
surface. Furthermore this comparison is expected to improve the fundamental understanding <strong>of</strong><br />
the results <strong>of</strong> tunneling spectroscopy on metal particles.<br />
Currently, a new setup is being built which will allow the deposition <strong>of</strong> size selected clusters on<br />
surfaces within an existing surface science apparatus. Scanning tunneling microscopy (STM)<br />
and ultraviolet photoelectron spectroscopy (UPS) will be performed on the deposited clusters<br />
and can be compared to the results <strong>of</strong> photoelectron spectroscopy obtained on the free clusters.<br />
Preliminary experiments have already been done on noble metal islands produced by deposition<br />
<strong>of</strong> metal atoms on rare gas films. First results show a dependence <strong>of</strong> the island Fermi edge<br />
position on the thickness <strong>of</strong> the isolating rare gas layer. Further measurements are underway.<br />
157
A - 40<br />
158<br />
Multiple Size-Selected Cluster Deposition:<br />
Epitaxial Growth at Thermal Energies<br />
Krist<strong>of</strong>fer Meinander, Kai Nordlund, and Juhani Keinonen<br />
Accelerator Laboratory, P.O.Box 43, FIN-00014 University <strong>of</strong> Helsinki, Finland<br />
It has been known for some time that when a small enough cluster lands on a singlecrystalline<br />
substrate it will align completely epitaxially upon impact [1]. In a previous study,<br />
using molecular dynamics simulations, it was noted that the upper size limit <strong>of</strong> Cu nanoclusters<br />
that will align epitaxially with a smooth (100) Cu substrate upon deposition at thermal energies<br />
is linearly dependent on temperature [2]. Deposition <strong>of</strong> clusters with sizes below the upper size<br />
limit will initially result in the formation <strong>of</strong> epitaxial structures on the surface <strong>of</strong> the substrate,<br />
however, as deposition continues clusters may impact on previously deposited clusters. The<br />
result <strong>of</strong> this may be a change in the likelihood <strong>of</strong> epitaxial alignment, as the deposition no<br />
longer takes place on a smooth surface, and hence a lowering in the upper size limit <strong>of</strong> clusters<br />
that can be used in the deposition <strong>of</strong> thick epitaxial films.<br />
Molecular dynamics simulations <strong>of</strong> multiple Cu cluster deposition were carried for different<br />
cluster sizes, over a temperature range <strong>of</strong> 0-750 K, in order to investigate the effect <strong>of</strong> cluster on<br />
cluster impacts to the upper size limit <strong>of</strong> epitaxial alignment. For each cluster size, several<br />
clusters were deposited in sequence, with a 2 ns interval between each cluster, on the same<br />
initially smooth, (100) Cu substrate. Through analysis <strong>of</strong> the degree <strong>of</strong> epitaxy between each<br />
deposition event, the maximum number <strong>of</strong> deposited clusters resulting in an epitaxial structure,<br />
for each specific cluster size, could be determined as a function <strong>of</strong> temperature.<br />
It was found that there is a substantial decrease in the upper size limit for epitaxial alignment<br />
when two clusters are deposited, as compared to that for the deposition <strong>of</strong> one cluster, for cases<br />
where the second cluster impacts directly on top <strong>of</strong> the one previously deposited. As the amount<br />
<strong>of</strong> deposited clusters increases, this decrease in the upper size limit is lowered, and ceases<br />
approximately after the fifth or sixth cluster.<br />
References<br />
[1] M. Yeadon et al., J. Elect. Microsc. 48 (Suppl.S), 1075 (1999).<br />
[2] K. Meinander, J. Frantz, K. Nordlund, and J. Keinonen, Thin Solid Films 45/1-2, 297-303 (2003).
C58 on HOPG<br />
A. Böttcher, P. Weis, S. Jester, A. Bihlmeier, D. Löffler, M. M. Kappes<br />
A - 41<br />
Institut für Physikalische Chemie, <strong>Universität</strong> Karlsruhe, Fritz-Haber-Weg 4, 76131 Karlsruhe, Germany<br />
The process <strong>of</strong> electron-impact induced fragmentation <strong>of</strong> C60 molecules has been exploited<br />
as an intense source <strong>of</strong> C58 + ions. The ionic beam was directed toward a HOPG substrate by a<br />
system <strong>of</strong> electrostatic lenses. A new solid material grows on the substrate as result <strong>of</strong> gentle<br />
deposition <strong>of</strong> C58 + ions (kinetic energy < 0.1 eV/atom). Thermal desorption spectra <strong>of</strong> the films<br />
created indicate that neither substrate-mediated decomposition nor dimerization <strong>of</strong> C58 occurs.<br />
The activation energy for desorption <strong>of</strong> C58 molecules from the HOPG surface is about 1 eV<br />
higher than found for C60 molecules on the same substrate. The apparent binding energy varies<br />
with increasing adsorbate coverage from 2 to 2.2 eV. The morphology <strong>of</strong> the deposited films<br />
has been investigated by means <strong>of</strong> AFM and STM. A fractal growth <strong>of</strong> 2D islands has been<br />
found to be the dominating deposition channel. The growth kinetics depends on the impact<br />
energy and surface temperature.<br />
159
A - 42<br />
160<br />
A comparative simulation <strong>of</strong> Al interaction with Ge and Si<br />
nanoclusters<br />
Ol’ga Ananyina, Olexandr Yanovs’ky<br />
SSEM Department, Zaporozhye State University, Zhukovsky Str. 66, Zaporozhye, 69063 Ukraine, e-mail:<br />
ananyina@zsu.zp.ua.<br />
Results <strong>of</strong> quantum-chemical calculations <strong>of</strong> Al-clusters (Al2, Al3, Al4) interaction with Si<br />
and Ge(100) surfaces are represented in this work. Al adsorption on clean semiconductor<br />
surfaces has an important technological significance as one <strong>of</strong> the ways <strong>of</strong> receiving metalsemiconductor<br />
contacts. Our calculations were carried out with the help <strong>of</strong> semi-empirical<br />
MNDO method (modified neglect <strong>of</strong> differential overlap) for Si33(Ge33) and Si67(Ge67) clusters,<br />
which are modeling the clean ordered Si(100)-(2×4) and Ge(100)-(2×1) surfaces. Cluster<br />
geometry and total energy, atom bonds orders, value <strong>of</strong> the electron density, atom orbital<br />
populations and molecular localized orbitals were calculated. Simulation <strong>of</strong> possible structures,<br />
formed by Al-clusters on Si(Ge) surfaces is the goal <strong>of</strong> this work, because forming <strong>of</strong> the certain<br />
adsorbates structure defines further growth <strong>of</strong> Al film.<br />
Two possible states <strong>of</strong> surface covered with Al2 clusters were received: the Al-Al “vertical” and<br />
“lateral” dimer models. Electronic states <strong>of</strong> Si(Ge)-(100) surface for different dimer models are<br />
compared.<br />
Fig.1. A result <strong>of</strong> Al2 - and Al3 adsorption on Ge(100)-(2×1) surface: a) a part <strong>of</strong> a cluster modelling clean<br />
Ge(100) surface with adsorbed Al2; “lateral” Al dimers forming; b) a part <strong>of</strong> a cluster modelling clean<br />
Ge(100) surface with adsorbed Al2; “vertical” Al dimers forming; c) cluster Ge63 with adsorbed Al3.<br />
Al3 adsorption on the semiconductors surfaces can be accompanied by the dissociation <strong>of</strong> Al3<br />
cluster on the Al atoms, which saturates bonds <strong>of</strong> surface atoms <strong>of</strong> Si-Si (Ge-Ge) dimers. But<br />
minimal total system energy corresponds to the state when Al3 cluster adsorbed on the surface<br />
without dissociation. An increase in aluminum cluster size causes the increase <strong>of</strong> cluster<br />
dissociation probability.<br />
The influence <strong>of</strong> surface defects on the processes <strong>of</strong> “surface - cluster” interaction and the<br />
possible reaction mechanisms at different coverage <strong>of</strong> such surfaces by dihydride and<br />
monohydride chemisorption phases are discussed. Comparative analysis <strong>of</strong> results <strong>of</strong> simulation<br />
for clusters <strong>of</strong> different size is carried out.
Characterization and Catalysis on a Well-defined Pt Cluster<br />
in NaY Zeolite<br />
Xiong Liu 1 , Rüdiger-A. Eichel 2 , Emil Roduner 1<br />
1 Institut für Physikalische Chemie, <strong>Universität</strong> Stuttgart, Pfaffenwaldring 55<br />
D-70569 Stuttgart, Germany<br />
2 Institute <strong>of</strong> Physical Chemistry III, Darmstadt University <strong>of</strong> Technology, Petersenstraße 20<br />
D-64287 Darmstadt, Germany<br />
A - 43<br />
Size effects <strong>of</strong> metal clusters play an important role in heterogeneous catalysis since the<br />
electronic properties, reactivity and selectivity <strong>of</strong> catalysts with a few atoms are strongly sizedependent.<br />
Platinum clusters dispersed in zeolites or on porous oxide supports are highly active<br />
catalysts for the oxidation <strong>of</strong> CO and residual hydrocarbons in automotive exhaust catalysis and<br />
for hydrogenation in petrochemical reactions. It is found that the catalyst performance increases<br />
with decreasing Pt cluster size. Usually, in supported metal catalysts the cluster size, shape and<br />
morphology are not uniform, which make the evaluation <strong>of</strong> catalytic properties complicated.<br />
Therefore, the preparation and characterization <strong>of</strong> homogeneous size clusters for understanding<br />
catalytic elementary steps and realizing catalysis on well-defined clusters is very desirable.<br />
Recently, we have demonstrated that under carefully controlled conditions it is possible to<br />
observe a single, well-defined small Pt cluster in zeolites by EPR spectroscopy. A highly<br />
symmetric cluster with 12 paramagnetic equivalent Pt atoms was characterized by continuous<br />
wave and pulse EPR. ENDOR and HYSCORE experiments reveal the proton hyperfine<br />
couplings <strong>of</strong> the adsorbed hydrogen on the surface. The observed species may be Pt13H12 n+ [1]<br />
or Pt13H20 n+ (n = +1 or +3) cluster with an icosahedral structure.<br />
Hydrogen or deuterium adsorbed on the Pt cluster exchanges and is desorbed and re-adsorbed<br />
reversibly. The desorption energy amounts to 0.69 eV per atom, in good agreement with<br />
theoretical values based on DFT calculations. Exposure to CO results in the decomposition <strong>of</strong><br />
the cluster and growth <strong>of</strong> new paramagnetic Pt-carbonyl clusters. Amazingly, reaction with O2<br />
is rather slow. SQUID measurements reveal that there is a large fraction <strong>of</strong> EPR silent<br />
paramagnetic and diamagnetic Pt species. They are partly in electron transfer equilibrium with<br />
the observed cluster.<br />
2600 2800 3000 3200<br />
Magnetic Field (G)<br />
6% Pt/NaY; reduction in H 2<br />
then exchanged by D 2<br />
6% Pt/NaY; reduction in H 2<br />
Figure 1. EPR spectrum <strong>of</strong> 6% Pt/NaY recorded at 20 K, demonstrating reversible exchange <strong>of</strong> hydrogen isotopes.<br />
References<br />
[1] T. Schmauke, R-A. Eichel, A. Schweiger, E. Roduner; Phys. Chem. Chem. Phys. 5, 3076 (2003).<br />
161
A - 44<br />
DFT-Investigations <strong>of</strong> coalescence behaviour <strong>of</strong> Si4 and Si7 clusters on<br />
surfaces<br />
162<br />
Wolfram Quester 1 , Dominik Fischer 1,2 and Peter Nielaba 1<br />
1 Fachbereich Physik, <strong>Universität</strong> <strong>Konstanz</strong>, 78457 <strong>Konstanz</strong><br />
2 IBM Zürich Research Laboratory, Säumerstraße 4, 8803 Rüschlikon<br />
Experimental results show that Si4 and Si7 clusters do not form islands <strong>of</strong> bulk Si on weakly<br />
interacting surfaces (HOPG). We investigated the coalescence behaviour using Density<br />
Functional Theory implemented in the CPMD code (www.cpmd.org).<br />
We calculated potential energy curves <strong>of</strong> two approaching Si4 clusters on two reaction channels.<br />
It could be shown that there exists a fusion barrier which is higher than room temperature.<br />
These calculations will be extended to Si7 clusters. To get informations about the influence <strong>of</strong><br />
the substrate a calculation <strong>of</strong> a Si4 cluster on a gold surface was perfomed. This simulation<br />
revealed that gold is not suited as substrate for depositing Si clusters.
A - 45<br />
Morphologies Studies <strong>of</strong> Mass Selected Au Clusters on Rutile TiO2 as a<br />
Function <strong>of</strong> Impact Energy and Surface Temperature<br />
P. Convers, R. Vallotton, R. Monot, W. Harbich<br />
Institut de Physique des Nanostructures,<br />
Ecole polytechnique Fédérale de Lausanne (EPFL),<br />
CH-1015 Lausanne<br />
In 1989 Haruta and coworkers have shown that small gold particles (diameter < 4 nm) are<br />
catalytically active [1]. Gold was found to be even more efficient for temperatures below 400°C<br />
than Pt, usually used for CO oxydation [2, 3]. More recent studies by Heiz et al. (Mass selected<br />
Aun deposited on MgO) and Anderson et al. (Mass selected Aun deposited on TiO2) report a<br />
pronounced size dependence <strong>of</strong> the catalytic activity [4, 5]. However informations on the<br />
morphology <strong>of</strong> the clusters is sparse. Wahlström et al. showed that atomic Au thermally<br />
deposited on a surface <strong>of</strong> TiO2(110) form clusters that are stabilized by oxygen vacancies at the<br />
surface [6]. The clusters are small enough for catalysis, however a temperature increase causes a<br />
sintering <strong>of</strong> the clusters and probably decreases the catalytic efficiency.<br />
To understand the clusters morphology as a function <strong>of</strong> temperature, we deposit mass-selected<br />
gold clusters with defined kinetic energy on a TiO2(110). The morphology is then studied by<br />
STM after different heating cycles up to 1000 K. We observe that large cluster sizes (n = 7) and<br />
high deposition energy (up to 4500 eV ) stabilize gold on the surface. Figure 1 is a typical STM<br />
image <strong>of</strong> a deposit <strong>of</strong> Au7 on TiO2 at 20 eV after a heating cycle at 800 K.<br />
References<br />
Figure 1. Au 7/TiO 2 at 20eV after annealing at 800K<br />
[1] M. Haruta, N. Yamada, T. Kobayashi, and S. Iijima, Journal <strong>of</strong> Catalysis 115, 301 (1989).<br />
[2] M. Haruta, Catalysis Today 36, 153 (1997).<br />
[3] M. Valden, X. Lai, and D. W. Goodman, Science 281, 1647 (1998).<br />
[4] A. Sanchez, S. Abbet, U. Heiz, W.-D. Schneider, H. Häkkinen, R. N. Barnett, and U. Landman, J.<br />
Phys. Chem. A 103, 9573 (1999).<br />
[5] S. Lee, C. Fan, T. Wu, and S. L. Anderson, J. Am. Chem. Soc. 126, 5682 (2004).<br />
[6] E. Wahlstrom, N. Lopez, R. Schaub, P. Thostrup, A. Ronnau, C. Africh, E. Laegsgaard, J.<br />
Norskov, and F. Besenbacher, Phys. Rev. Lett. 90, 026101 (2003).<br />
163
A - 46<br />
164<br />
Mass-selected Nanocrystal Superlattices<br />
J. T. Lau 1 , H.Weller 2 , T. Möller 1<br />
1 Technische <strong>Universität</strong> Berlin, IAPF PN 3-1, Hardenbergstraße 36, D-10623 Berlin<br />
2 <strong>Universität</strong> Hamburg, Institut für Physikalische Chemie, Grindelallee 117, D-20146 Hamburg<br />
Nanocrystal superlattices built <strong>of</strong> identical particles are expected to exhibit novel electronic and<br />
optical properties that can be tuned by particle size and interparticle distance. Below a distance<br />
<strong>of</strong> approx. 2–5 Å, for example, coherent tunneling coupling or exchange coupling between<br />
nanocrystals is expected because <strong>of</strong> wave function overlap.<br />
We will present the design <strong>of</strong> our experiment and discuss how superlattice properties can be<br />
probed by X-ray absorption, X-ray photoelectron spectroscopy, X-ray scattering and<br />
photoluminescence spectroscopy.
165
Author Index<br />
167
168
Abbet, S.......................................................... 53<br />
Aguado, A. ................................................... 125<br />
Ahmed, M....................................................... 65<br />
Akola, J......................................................... 149<br />
Alamanova, D............................................... 105<br />
Alexandrova, A. N........................................ 112<br />
Ananyina, O. ................................................ 160<br />
Andersen, J. U. ............................................. 129<br />
Anderson, S. L.................................................. 7<br />
Andersson, M. ................................................ 50<br />
Antonietti, J. M....................................... 53, 154<br />
Arredondo, M. G. ........................................... 49<br />
Asmis, K. R. ............................................. 55, 59<br />
Bahat, M....................................................... 118<br />
Balaj, O. P. ..................................................... 25<br />
Balakrishnan, K............................................ 151<br />
Balbás, L. C.................................................... 57<br />
Balteanu, I. ..................................................... 25<br />
Barat, M.......................................................... 13<br />
Barke, I......................................................... 157<br />
Barnakov, Y. A................................................. 9<br />
Bartels, Chr..................................................... 69<br />
Baruah, S. ....................................................... 96<br />
Bechthold, P. S. .............................................. 51<br />
Belosludov, R. V. ............................................. 9<br />
Benz, L. .......................................................... 16<br />
Berdunov, N. ................................................ 151<br />
Berry, R. St................................................... 126<br />
Bertram, N................................................ 88, 89<br />
Beuhler, R. J. .................................................. 54<br />
Beyer, M. K.................................................... 25<br />
Bihlmeier, A. ................................................ 159<br />
Blaum, K. ....................................................... 96<br />
Block, M......................................................... 96<br />
Blom, M. N................................................... 106<br />
Böcker, D. .................................................... 157<br />
Boese, A. D. ................................................. 116<br />
Boldyrev, A. I............................................... 112<br />
Bolton, K. ....................................................... 41<br />
Bonačić-Koutecký, V. ........................ 11, 62, 75<br />
Bondybey, V. E. ............................................. 25<br />
Böttcher, A. .................................................. 159<br />
Bousquet, G.................................................... 73<br />
Bouteiller, Y. .................................................. 12<br />
Bowen, Jr., K. H............................................... 6<br />
Bowers, M. T.................................................. 16<br />
Bréchignac, C. .................................................. 3<br />
Brown, S....................................................... 155<br />
Brück, J........................................................... 47<br />
Brümmer, M. .................................................. 59<br />
Buck, U................................................... 29, 143<br />
Bulusu, S. ..................................................... 112<br />
Buratto, S. K................................................... 16<br />
Bürgel, Chr..................................................... 62<br />
Burmeister, F.................................................. 66<br />
Campbell, E. E. B............................. 40, 68, 132<br />
Castleman Jr., A. W.................................. 26, 62<br />
Cederbaum, L. S........................................... 144<br />
Chaudhuri, A...................................................96<br />
Chelikowsky, J. R. ..........................................22<br />
Cheshnovsky, O. .............................................93<br />
Chrétien, St. ....................................................16<br />
Christen, W. ..................................................115<br />
Claas, P. ..........................................................72<br />
Concina, B. .....................................................38<br />
Convers, P.....................................................163<br />
Cordes, J. ........................................................89<br />
Danylchenko, O. G. ......................................124<br />
de Heer, W.......................................................19<br />
Dedonder-Lardeux, C. ....................................13<br />
Denifl, S..................................................38, 131<br />
Desfrançois, C...........................................12, 13<br />
Dietsche, R......................................................88<br />
Ding, F. ...........................................................41<br />
Dinh, M...........................................................73<br />
Dmitruk, I....................................................9, 85<br />
Dong, Y...........................................................48<br />
Donges, J.........................................................32<br />
Döppner, T......................................................71<br />
Droppelmann, G..............................................72<br />
Duncan, M. A....................................................5<br />
Eberhardt, W.............................................51, 66<br />
Echt, O. ...................................................38, 129<br />
Ehrler, O. T. ....................................................39<br />
Eichel, R.-A. .................................................161<br />
Elam, J. W.....................................................152<br />
Engelke, M......................................................74<br />
Fan, Ch..............................................................7<br />
Fanourgakis, G. S..........................................119<br />
Fayeton, J. A. ..................................................13<br />
Fedor, J. ........................................................129<br />
Fehrer, F..........................................................73<br />
Feil, S......................................................38, 131<br />
Fennel, Th. ......................................................71<br />
Fernández, E. M..............................................57<br />
Fielicke, A...............................................45, 103<br />
Fischer, D......................................................162<br />
Fischer, T. .......................................................88<br />
Fontanella, S. ..................................................59<br />
Frenzel, J.......................................................139<br />
Furche, F. ........................................................39<br />
Gadéa, F. X. ..................................................133<br />
Galak, M. ........................................................85<br />
Ganteför, G. ..................................61, 74, 88, 89<br />
Gemming, S. ...................................................30<br />
Giniger, R........................................................93<br />
Glaser, L. ........................................................17<br />
Głuch, K..........................................38, 129, 131<br />
Grégoire, G. ..............................................12, 13<br />
Grigoryan, V. G. ...........................................105<br />
Gromov, A. .....................................................40<br />
Haberland, H...................................................32<br />
Hagelberg, F..................................................129<br />
Häkkinen, H................................46, 87, 97, 104<br />
Hammer, B......................................................56<br />
Hampe, O........................................................52<br />
169
Hansen, K................................. 40, 68, 129, 132<br />
Harbich, W. .................................................. 163<br />
Hedén, M.................................................. 40, 68<br />
Heiz, U. .................................................. 53, 154<br />
Herfurth, F...................................................... 96<br />
Herlert, A.......................................... 96, 98, 110<br />
Higashimine, K............................................. 150<br />
Hippler, T. ...................................................... 32<br />
Hock, Chr. ...................................................... 69<br />
Horoi, M......................................................... 28<br />
Hövel, H. ...................................................... 157<br />
Hrivňák, D............................................ 130, 133<br />
Huang, X. ....................................................... 22<br />
Huber, B. .............................................. 111, 153<br />
Ikeda, K. S...................................................... 76<br />
Irawan, Th. ................................................... 157<br />
Jackson, K. A. .......................................... 28, 80<br />
Janeček, I...................................................... 130<br />
Janssens, E.................................................... 108<br />
Jena, P............................................................. 23<br />
Jester, S......................................................... 159<br />
Jeyadevan, V. ................................................... 9<br />
Johansson, M. P.............................................. 42<br />
Jones, H. ....................................................... 154<br />
Jonsson, F....................................................... 40<br />
Joswig, J.-O. ......................................... 138, 139<br />
Jouvet, C......................................................... 13<br />
Judai, K........................................................... 53<br />
Jusélius, J........................................................ 42<br />
Kaiser, B....................................................... 155<br />
Kalus, R........................................ 123, 130, 133<br />
Kang, H. ......................................................... 13<br />
Kantarci, Z.................................................... 118<br />
Kappes, M. M........................... 39, 52, 106, 159<br />
Karlický, F.................................................... 123<br />
Kasuya, A................................................... 9, 85<br />
Kato, K. ........................................................ 150<br />
Kawazoe, Y. ..................................................... 9<br />
Kaya, K........................................................... 31<br />
Keinonen, J................................................... 158<br />
Kellerbauer, A. ............................................... 96<br />
Kemper, P....................................................... 16<br />
Kern, K........................................................... 15<br />
Khan, F. A. ..................................................... 49<br />
Khanna, S. N. ................................................. 86<br />
Kim, J. H. ....................................................... 65<br />
Kim, Y. D..................................... 61, 74, 88, 89<br />
Kim, Y.-T. .................................................... 150<br />
Kimble, M. L.................................................. 62<br />
Kiran, B. ........................................... 58, 60, 112<br />
Kjellberg, M. ................................................ 132<br />
Klingeler, R. ................................................... 51<br />
Kluge, H.-J. .................................................... 96<br />
Knickelbein, M. B. ......................................... 20<br />
Kobayashi, T. ................................................. 76<br />
Kolmakov, A. ................................................. 16<br />
Kondow, T...................................................... 21<br />
Kordel, M. .................................................... 106<br />
Koskinen, P. ................................................. 104<br />
170<br />
Kostko, O................................................32, 109<br />
Kovalenko, S. I. ............................................124<br />
Krause, T.......................................................115<br />
Kresin, V. V............................................67, 107<br />
Kresin, V. Z. ...................................................67<br />
Kronik, L.........................................................22<br />
Kryzhevoi, N. V............................................144<br />
Kudo, T. ............................................................9<br />
Kuhnen, R. ......................................................69<br />
Kumar, V. .........................................................9<br />
kyun Lee, E.....................................................37<br />
Lagutschenkov, A. ..................................47, 119<br />
Landman, U. ...................................................53<br />
Lassesson, A. ................................................110<br />
Lau, J. T. .......................................................164<br />
Leavitt, A. J.....................................................49<br />
Lecomte, F. .....................................................12<br />
Lee, B............................................................152<br />
Lee, S. ...............................................................7<br />
Li, J. ........................................................58, 112<br />
Li, X..........................................................58, 60<br />
Lievens, P................................................50, 108<br />
Lifshitz, C. ......................................................38<br />
Lightstone, J....................................................54<br />
Lim, D. C. .................................................61, 88<br />
Liu, X............................................................161<br />
Liu, Z. .......................................................9, 145<br />
Löffler, D. .....................................................159<br />
López, J. M. ..................................................125<br />
Lopez-Salido, I..........................................61, 88<br />
Lucas, B. .........................................................12<br />
Lüttgens, G......................................................51<br />
Makmal, A. .....................................................22<br />
Malakzadeh, A. ...............................................69<br />
Mamykin, S. V..................................................9<br />
Manninen, M.................................................149<br />
Mariotto, G....................................................151<br />
Märk, T. D. .....................................38, 129, 131<br />
Martinez, F......................................98, 110, 131<br />
Martins, M. .....................................................17<br />
Marx, G.............................................96, 98, 110<br />
Matt-Leubner, S. .....................................38, 129<br />
Meijer, G...........................................45, 59, 103<br />
Meinander, K. ...............................................158<br />
Meiwes-Broer, K.-H. ................................70, 71<br />
Metiu, H..........................................................16<br />
Michalski, M.................................................154<br />
Milczarek, G. ....................................................9<br />
Mitani, T. ......................................................150<br />
Mitrić, R....................................................62, 75<br />
Mitsui, M. .......................................................31<br />
Molina, L. M...................................................56<br />
Möller, T. ......................................................164<br />
Monot, R. ......................................................163<br />
Moore, N. A....................................................62<br />
Moro, R.........................................................107<br />
Moseler, M....................................104, 111, 153<br />
Mukherjee, M..................................................96<br />
Mukovskii, Y. M...........................................151
Murakami, J.................................................... 24<br />
Murphy, S..................................................... 151<br />
Nakajima, A. ............................................ 31, 79<br />
Neeb, M.................................................... 51, 66<br />
Neukermans, S.............................................. 108<br />
Neumaier, M................................................... 52<br />
Neumark, D. M......................................... 10, 65<br />
Niedner-Schatteburg, G.................... 47, 81, 119<br />
Nielaba, P. .................................................... 162<br />
Niemietz, M.................................................... 74<br />
Nirasawa, T. ..................................................... 9<br />
Nordlund, K.................................................. 158<br />
Ohshima, K................................................... 150<br />
Ohsuna, T. ........................................................ 9<br />
Ohta, T............................................................ 21<br />
Osaka, K....................................................... 150<br />
Ovchinnikov, Y. N. ........................................ 67<br />
Palmer, R. E. .................................................. 14<br />
Pankewitz, T................................................... 47<br />
Park, C. Y..................................................... 156<br />
Park, J............................................................. 37<br />
Parks, J. H................................................. 8, 106<br />
Patterson, M. .................................................. 54<br />
Pedersen, D. B................................................ 45<br />
Pellin, M. J. .................................................. 152<br />
Peterka, D. S................................................... 65<br />
Pfeffer, B. ....................................................... 47<br />
Pontius, N....................................................... 51<br />
Popok, V....................................................... 132<br />
Prasalovich, S. .............................................. 132<br />
Proykova, A.................................................. 126<br />
Przystawik, A. ................................................ 70<br />
Ptasińska, S............................................. 38, 131<br />
Quester, W.................................................... 162<br />
Rabinovitch, R.............................................. 107<br />
Radcliffe, P..................................................... 70<br />
Ratsch, Chr................................................... 103<br />
Rayner, D. M.................................................. 45<br />
Reif, M. .......................................................... 17<br />
Reinhard, P.-G................................................ 73<br />
Ritter, H.......................................................... 98<br />
Roduner, E.................................................... 161<br />
Romanyuk, V. ............................................ 9, 85<br />
Ronen, S. ........................................................ 93<br />
Rönnow, E...................................................... 40<br />
Rosén, A......................................................... 41<br />
Roßteuscher, T................................................ 25<br />
Röttgen, M. A................................................. 53<br />
Roy, S................................................... 137, 138<br />
Rytkönen, K. ................................................ 149<br />
Samovarov, V. N.......................................... 124<br />
Santambrogio, G............................................. 59<br />
Santa-Nokki, T. .............................................. 46<br />
Sarfraz, A. .................................................... 115<br />
Sarkar, P. ...................................................... 138<br />
Sauer, J. .......................................................... 59<br />
Sawada, S. ...................................................... 76<br />
Scheier, P........................................ 38, 129, 131<br />
Schermann, J.-P........................................ 12, 13<br />
Schmidt, M......................................................32<br />
Schneider, H..........................................116, 117<br />
Schooss, D. ...................................................106<br />
Schulz, C.-P. ...................................................72<br />
Schweikhard, L. ................................96, 98, 110<br />
Scott, S..........................................................155<br />
Seifert, G.........................................30, 104, 139<br />
Seifert, S. ......................................................152<br />
Serrano, D. ......................................................49<br />
Shim, J. ...........................................................37<br />
Shimizu, Y. .....................................................76<br />
Shinoda, K. .......................................................9<br />
Shrestha, S. P. ...............................................156<br />
Shvets, I. V....................................................151<br />
Silverans, R. E. .............................................108<br />
Simard, B. .......................................................45<br />
Sivamohan, R....................................................9<br />
Springborg, M................. 48, 105, 137, 138, 139<br />
Srinivas, S. ......................................................80<br />
Stairs, J..........................................................106<br />
Stanzel, J. ........................................................66<br />
Stegemann, B................................................155<br />
Steinbach, Chr.........................................29, 143<br />
Stienkemeier, F. ..............................................72<br />
Suematsu, H..................................................150<br />
Sun, Q. ............................................................23<br />
Sundararajan, V. ...............................................9<br />
Sundholm, D. ..................................................42<br />
Suraud, E.........................................................73<br />
Swenson, D. R. ...............................................94<br />
Takada, M. ....................................................150<br />
Terasaki, A......................................................21<br />
Terasaki, O........................................................9<br />
Tiggesbäumker, J. .....................................70, 71<br />
Tikhonov, G. Y. ............................................152<br />
Tohji, K.............................................................9<br />
Tomczyk, N. A..............................................152<br />
Tong, X. ..........................................................16<br />
Tono, K. ..........................................................21<br />
Torres, M. B....................................................57<br />
Uruga, T........................................................150<br />
Vaara, J. ..........................................................42<br />
Vajda, St. ......................................................152<br />
Vallotton, R...................................................163<br />
Veldeman, N. ..........................................50, 108<br />
Velegrakis, M..................................................99<br />
Vetter, M.........................................................47<br />
Vítek, A.........................................................123<br />
von Gynz-Rekowski, F. ..................................88<br />
von Helden, G.........................................45, 103<br />
von Issendorff, B............... 32, 69, 109, 111, 157<br />
Wallace, W. T. ................................................49<br />
Walsh, N. ......................................................110<br />
Walter, L. ......................................................106<br />
Walter, M........................................................97<br />
Wang, C. .........................................................65<br />
Wang, L.-S........................................58, 60, 112<br />
Wang, Q..........................................................23<br />
Wang, X........................................................108<br />
171
Weber, J. M. ................................... 39, 116, 117<br />
Weigend, F. .................................................... 52<br />
Weis, P. ........................................................ 159<br />
Weller, H. ..................................................... 164<br />
Whetten, R. L. ................................................ 49<br />
White, M. G.................................................... 54<br />
Wies, St. ......................................................... 47<br />
Winans, R. E................................................. 152<br />
Wolf, I. ........................................................... 93<br />
Wörz, A. S...................................................... 53<br />
Wöste, L. .................................................... 4, 59<br />
Wu, T................................................................ 7<br />
Wurth, W.................................................. 17, 81<br />
172<br />
Wyrwas, R. B..................................................49<br />
Xantheas, S. S. ..............................................119<br />
Xia, C............................................................107<br />
Yamaguchi, W. ...............................................24<br />
Yanovs’ky, O................................................160<br />
Yazidjian, Ch. .................................................96<br />
Yeschenko, O..................................................85<br />
Yin, Ch..........................................................157<br />
Yoon, B...........................................................53<br />
Zeng, X. Ch...................................................112<br />
Zhai, H. J...........................................58, 60, 112<br />
Zhang, H.-F.....................................................58
Time<br />
8.30 a.m.<br />
9.15 a.m.<br />
10.00 a.m.<br />
10.30 a.m.<br />
11.15 a.m.<br />
12.00 p.m.<br />
2.00 p.m.<br />
-<br />
4.00 p.m.<br />
5.00 p.m.<br />
5.45 p.m.<br />
Sunday Monday<br />
Tuesday Wednesday Thursday Friday<br />
28 February 05<br />
27 February 05<br />
8:20 Opening<br />
1 March 05 2 March 05 3 March 05 4 March 05<br />
Arrival<br />
C. Bréchignac<br />
Metal Clusters and Oxygen<br />
L. Wöste<br />
Reactivity Ag+Au Clusters<br />
M. A. Duncan<br />
IR <strong>of</strong> Metal Complexes<br />
K. H. Bowen, Jr.<br />
Diffuse Electron States<br />
S. L. Anderson<br />
Model Au Catalysts<br />
J. H. Parks<br />
Structural Order in Metal Clusters<br />
D. M. Neumark<br />
Dynamics and Droplets<br />
V. Bonačić-Koutecký<br />
Tailoring functionality by size<br />
C. Desfrancois<br />
New Infrared Spectroscopy Tech.<br />
C. Jouvet<br />
The H-Transfer Reaction<br />
R. E. Palmer<br />
Immobilisation <strong>of</strong> Proteins<br />
K. Kern<br />
Architecture at surfaces<br />
W. A. de Heer<br />
Cluster Ferroelectricity<br />
M. B. Knickelbein<br />
Molecular Magnets<br />
A. W. Castleman, Jr.<br />
Cluster Assembled Materials<br />
M. F. Jarrold<br />
Al/Ga Cluster Melting<br />
HT 3 HT 8<br />
HT 5 HT 10<br />
HT 7<br />
K. Kaya<br />
S<strong>of</strong>t-Nano-Molecular Clusters<br />
H. Haberland<br />
Melting and Magic Numbers<br />
6.30 p.m. A. Kasuya (CdSe) n Clusters S. K. Buratto Ag n+Au n on TiO Concluding Remarks (P. Jena)<br />
*) Please see Table <strong>of</strong> Contents for the Poster Sessions<br />
Schedule<br />
Fermion/Boson Clusters+Catalysis<br />
C<strong>of</strong>fee<br />
Lunch<br />
Discussions<br />
K. Tono Oxidation <strong>of</strong> Cr n/Mn n<br />
L. Kronik Mag. Semiconductors<br />
Q. Sun Nanobullet for Tumor<br />
J. Murakami N 2 on supported W n<br />
M. Beyer CO-Oxidation on Pt n<br />
Special P. Leiderer Talk 15<br />
Potentials+Prospects <strong>of</strong> Nanoscience<br />
M. Horoi Phase Transitons<br />
U. Buck Na-doped H 2O Clusters<br />
G. Seifert MoS Clusters<br />
7.00 p.m.<br />
Dinner Conference<br />
8.30 p.m.<br />
Poster<br />
M. Martins Magnetic Clusters<br />
Poster<br />
Dinner<br />
9.15 p.m.<br />
Session A *)<br />
U. Landman<br />
Session B *)<br />
Post Conference Session<br />
Sketch: Scientific Dialogology - four<br />
techniques for asking proper questions<br />
Departure after<br />
breakfast