aktualisiertes pdf - DPG-Tagungen

MO 19.6 Fr 12:15 HS 332
HIGH RESOLUTION STUDY OF DELOCALIZED ELEC-
TRON CLOUDS BY PHOTOIONIZATION OF C60 IN
SMALL ENERGY STEPS — •Sanja Korica 1 , Axel
Reinköster 1 , Burkhard Langer 2 , Daniel Rolles 1 , Slobodan
Cvejanović 1 , Jens Viefhaus 1 , and Uwe Becker 1 —
1 Fritz-Haber-Institut der MPG, Faradayweg 4-6, D-14195 Berlin,
Germany — 2 Max-Born-Institut, Max-Born-Str. 2a, D-14489 Berlin,
Germany
Recent measurements of the non-resonant valence photoemission of
C60 in the oscillatory regime have shown that advanced theoretical calculations
are capable to describe the measured cross-section behavior in
great detail [1]. We have made measurements with high photon energy
resolution and small energy steps in order to reveal the predicted resonance
structures experimentally. The characteristic oscillations in the
partial photoionization cross sections of C60 are analysed in terms of geometrical
properties of both, the cage structure and the distribution of the
delocalized electron cloud of the highest occupied molecular orbitals. The
analysis is based on the Fourier transform of the cross section oscillations,
the results are corroborated by different theoretical models. In contrast
to this good overall agreement between theory and experiment there is
striking disagreement with respect to discrete resonance structure in the
partial cross sections predicted by the theoretical calculations. Possible
reasons for this behavior are discussed.
[1] A. Rüdel, R. Hentges, U. Becker, H.S. Chakraborty, M.E. Madjet, and
J.M. Rost, Phys. Rev. Lett. 89 (2002), 125503 and references therein
MO 19.7 Fr 12:30 HS 332
Fragmentation Dynamics of C60 — •Mark Boyle 1 , Ihar
Shchatsinin 1 , Tim Laarmann 1 , C.P. Schulz 1 , and I.V. Hertel 1,2
— 1 Max Born Institut, Max-Born-Str. 2A, 12489 Berlin — 2 Freie
Universität Berlin, Arnimallee 14, 14195 Berlin
The C60 cluster is an interesting model system for studying lasermatter
interaction. The high degree of symmetry facilitates the studies
MO 20 Schwingung und Rotation
of a complex system. One characteristic of great interest is the energy
redistribution after the initial fs-laser pulse excitation. The mechanisms
and time scales for energy redistribution are of considerable interest for
understanding and controlling their dynamical behavior. Fragmentation
can provide an indirect measure of the transfer of energy from the electronic
to the vibrational degrees of freedom. Pump-probe measurements
have been made to monitor the fragmentation of C60 on the femtosecond
and picosecond time scale. This presentation will cover recent results
from pump-probe measurements, as well as discuss the applications of
pulse shaping to control the dynamics.
MO 19.8 Fr 12:45 HS 332
Photoionisation als Struktursonde von delokalisierten Elektronen
in Fullerenen — •B. Langer — Max-Born-Institut für Nichtlineare
Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489
Berlin
Die Örtliche Verteilung von delokalisierten Elektronen ist im
allgemeinen einer experimentellen Bestimmung nur schwer zugänglich.
Erst in jüngster Zeit hat sich gezeigt, daß für eine bestimmte Klasse
von Clustern, aber insbesondere für Fullerne, eine derartige Analyse
möglich ist. Die spezifische Potentialstruktur dieser Fullerene gibt Anlaß
zu charakteristischen Oszillationen in den partiellen Photoionisations–
Wirkungsquerschnitten der äußeren Valenzschalen, die Informationen
über die Verteilung der delokalisierten Elektronen im reziproken
Fourier–Raum enthalten. Dies wurde kürzlich für C60 [1] gezeigt. Eine
analoge Untersuchung an C70 wurde mit dem Ziel durchgeführt, zu
prüfen, inwieweit diese Methode auf dieses nicht vollkommen sphärische
Molekül übertragbar ist. Die Messungen zeigen, daß die Methode in
der Tat auf eine weitere Gruppe von Fullerenen anwendbar ist, wobei
gerade die spezifischen Unterschiede zwischen C60 und C70 in den
charakteristischen Oszillationen zutage treten.
[1] A. Rüdel, R. Hentges, U. Becker, H. S. Chakraborty, M. E. Madjet,
and J. M. Rost, Phys. Rev. Lett., 89, 125503 (2002) and references therein.
Zeit: Freitag 11:00–12:45 Raum: HS 355
MO 20.1 Fr 11:00 HS 355
Gas Phase Investigation of Strong Hydrogen Bonds by
Infrared Spectroscopy — •Eva Cristina Kaposta 1 , Nicholas
L. Pivonka 2 , Mathias Bruemmer 1 , Gabriele Santambrogio 1 ,
Carlos Cibrian Uhalte 1 , Matt Nee 2 , Andreas Osterwalde
2 , Gert von Helden 3 , Gerard Meijer 3 , Daniel M.
Neumark 2 , Ludger Woeste 1 , and Knut R. Asmis 3 — 1 Institut
fuer Experimentalphysik, Freie Universitaet Berlin, Arnimallee 14,
D-14195 Berlin, Germany — 2 Department of Chemistry, University of
California, Berkley, California 94720 USA — 3 Fritz-Haber-Institut der
Max-Planck-Gesellschaft, Abteilung Molekuelphysik, Faradayweg 4-6,
D-14195 Berlin, Germany
Hydrogen bonds govern physical and chemical phenomena ranging
from the solvent properties of water to the structure of proteins and
nucleic acids. Strong hydrogen bonds are characterized by low exchange
barriers and often the central proton or hydrogen atom is shared equally
by the two heteroatoms. In the present work we characterize the infrared
(IR) spectroscopy of strong hydrogen bonds in the gas phase.
IR-photodissociation spectra were measured for (BrHBr) − , (BrDBr) − ,
(BrHI) − and (BrDI) − , model compounds, which function as precursors
for transition state spectroscopy experiments, as well as of the protonated
water dimer H5O + 2 . The spectra were measured in the region from 625
to 1700 wave numbers by combining a tandem mass spectrometer with
the output of the tunable, intense free electron laser FELIX.
MO 20.2 Fr 11:15 HS 355
Direct observation of Tiers in the Energy Landscape of a Chromoprotein:
a Single-Molecule study — •Clemens Hofmann 1 ,
Martin Richter 1 , Thijs J. Aartsma 2 , Hartmut Michel 3 , and
Jürgen Köhler 1 — 1 Experimental Physics IV, University of Bayreuth
— 2 Department of Biophysics, Leiden University — 3 Department of
Molecular Membrane Biology, MPI of Biophysics, Frankfurt
Pigment-protein complexes play an important role in light-harvesting
of bacterial photosynthesis. From x-ray crystallography it is known that
70
the light-harvesting 2 complex (LH2) from Rhodospirillum molischianum
consists of 24 BChl a molecules arranged in C8 symmetry in two concentric
rings containing eight and sixteen pigments, respectively. The
electronically excited states of the eight-ring (B800) are mainly localised
on individual BChl a molecules due to the weak coupling between the
chromophores. A sensitive tool to monitor structural fluctuations of the
protein backbone in the local environment of the chromophore is provided
by recording the changes of the spectral positions of the pigment
absorptions as a function of time. The data provide information about
the organisation of the energy landscape of the protein in distinct tiers
that can be characterised by an average barrier height. In addition, a
clear correlation for the transition rates between those states and the
energy separation of the levels is uncovered.
[1] Clemens Hofmann, Thijs J. Aartsma, Hartmut Michel,
Jürgen Köhler, PNAS 100 15534-15538 (2003).
[2] Clemens Hofmann, Thijs J. Aartsma, Hartmut Michel,
Jürgen Köhler New J. Phys. (in press).
MO 20.3 Fr 11:30 HS 355
Free Rotation of Paraterpenyl in PMMA Nanocavities —
•Christian Spitz, David von Seggern, and Ralf Menzel —
Universität Potsdam, Institut für Physik, Am Neuen Palais 10, 14469
Potsdam
By the use of transient grating diffraction measurements the population
dynamics as well as the polarization dynamics in thin films can be
investigated on a ps timescale. In this technique a pair of pump beams
modulates the sample absorption with its interference pattern. Subsequently,
a probe beam is diffracted on the population grating as well as
on the polarization grating.
In this paper the excited state behaviour of p-terphenyl in cyclohexane
solution and in a rigid poly(methyl methacrylate) (PMMA) film is
reported. In both cases the signal shows a biexponential decay with a
slower component corresponding to the excited state lifetime. The faster
time constant is predicted for rotational reorientation in the case of liquid
solution. Unexpectedly in the rigid film this reorientation becomes