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MO 3.6 Mo 12:15 HS 355
Jet-cooled neutral and cationic PAHs studied by cavity
ring-down spectroscopy — •A. Staicu 1 , O. Sukhorukov 1 ,
G. Rouillé 2,3 , E. Diegel 1 , F. Huisken 2,3 , and Th. Henning
3 — 1 Astrophysikalisches Institut und Universitätssternwarte,
Friedrich-Schiller-Universität Jena — 2 Institut für Festkörperphysik,
Friedrich-Schiller-Universität Jena — 3 Max-Planck-Institut für
Astronomie, Heidelberg
Polycyclic aromatic hydrocarbons (PAHs) are relevant molecules for
astrophysics. It is expected that they are present in the interstellar
medium (ISM), and they are considered as possible carriers of the diffuse
interstellar bands (DIBs). To prove this, absorption spectra of PAHs
under astrophysical conditions should be obtained. Collision-free environment
and low temperatures similar to those encountered in the ISM can
be obtained in the laboratory in supersonic jets. We have chosen cavity
ring-down spectroscopy (CRDS) to measure direct absorption spectra of
jet-cooled PAHs in their neutral and cationic form. The absorption spectra
of anthracene, pyrene, and fluorene, corresponding to their electronic
transitions in the UV spectral range, have been studied. On the other
hand, the cations of small PAHs exhibit absorption bands in the visible
range where DIBs are observed. First CRDS experiments on the cations
of naphthalene and anthracene were successful and their results will be
presented.
MO 3.7 Mo 12:30 HS 355
IBBCEAS an Flüssigkeiten — •Sven E. Fiedler 1 , Achim Hese 1
und Albert A. Ruth 2 — 1 Technische Universität Berlin, Institut für
Atomare Physik und Fachdidaktik, Hardenbergstr. 36, 10623 Berlin —
2 Department of Chemistry, National University of Ireland, College Cork,
Ireland
In diesem Beitrag wird die neue, hochempfindliche und bisher nur auf
Moleküle in der Gasphase angewendete Technik der Incoherent Broad-
Band Cavity Enhanced Absorption Spectroscopy (IBBCEAS) kurz vorgestellt.
Die ersten Ergebnisse von Messungen an Flüssigkeiten und Molekülen
in Lösung werden hinsichtlich der Empfindlichkeit und Potential
dieser Methode diskutiert.
MO 3.8 Mo 12:45 HS 355
Spectroscopy of the XeC2 molecule in Xenon, Argon and
Krypton matrices — •Marcin Frankowski, Alice M.
Smith-Gicklhorn, and Vladimir E. Bondybey — Institut
für Physikalische und Theoretische Chemie, Technische Universität
München, Lichtenbergstr. 4, 85748, Garching, Germany
A self-igniting DC-electric discharge of C2H2 in Xe (matrix gas) or
C2H2/Xe in Ar or Kr (matrix gases) is used to produce and study the
XeC2 molecule in these various rare gases at 12 K. Unlike in Ar and Kr
matrices, the well-known electronic spectra of C2 is completely absent in
a Xe matrix. This together with annealing experiments in Ar matrices
indicate that ground state Xe and C2 react uniquely and without a barrier
to form the XeC2 molecule. The infrared-active C-C stretch of this
compound is found to be close to the C-C stretching frequency of C − 2 anion,
in excellent agreement with our density functional theoretical (DFT)
calculations which yield a XeCC singlet species bent by 148.6 o and with
substantial charge separation approaching Xe + C − 2 and a notably short,
2.107 ˚A, Xe-C bond. The spectra of the Xe- 13 C- 12 C, Xe- 12 C- 13 C and Xe-
13 C- 13 C species are also obtained and the isotopic shifts are in excellent
agreement with the DFT predictions, although not sufficient to distinguish
a bent from a linear structure.
Numerous broad absorptions centered near 423 nm (in Xe) are observed
which are clearly due to the XeC2 molecule. Laser-induced fluorescence
studies reveal a near-infrared emission likely due to XeC2 but
not yet understood.
MO 4 Femtosekundenspektroskopie: Elektrontransfer
Zeit: Montag 11:00–12:45 Raum: HS 315
MO 4.1 Mo 11:00 HS 315
Ultraschnelle photoinduzierte Prozesse biologisch relevanter
Moleküle in der Gasphase: Indol, Pyrrol, Adenin — •Helmut
Lippert 1 , Volker Stert 1 , Ingolf Volker Hertel 1,2 und Wolfgang
Radloff 1 — 1 Max-Born-Institut, Max-Born-Str. 2A, D-12489
Berlin — 2 Freie Universität Berlin, Arnimallee 14, D-14195 Berlin
Die aromatischen Heterocyclen Indol, Pyrrol und Adenin wurden nach
Anregung bei λpump = 250 nm bzw. 263 nm mittels Femtosekunden
Pump-Probe Spektroskopie im Molekularstrahl untersucht. Die Resultate
werden mit Hinblick auf eine mögliche Population des repulsiven πσ ∗
Zustands diskutiert, der als wesentlich für die Photophysik derartiger
Chromophore angesehen wird [1]. Die Addition nur weniger Solvensmoleküle
wie Wasser oder Ammoniak beeinflußt die Dynamik entscheidend,
was durch Studien zu Indol(NH3)n Clustern bereits eindrucksvoll belegt
worden ist [2]. Für Pyrrol konnten erstmalig mit fs Laserimpulsen neutrale
H Atome als Fragmente mittels (2+1)REMPI bei λprobe = 243 nm
[3] zeitaufgelöst nachgewiesen werden.
[1] W. Domcke, A.L. Sobolewski, Science 302, 1693 (2003).
[2] H. Lippert, V. Stert, L. Hesse, C.P. Schulz, I.V. Hertel, W. Radloff,
JPC A 107, 8239 (2003).
[3] J. Wei, A. Kuczmann, J. Riedel, F. Renth, F. Temps, PCCP 5, 315
(2003).
MO 4.2 Mo 11:15 HS 315
The ultrafast photodynamics of indole — •Tanja Bizjak 1 ,
Prem B. Bisht 2 , Stefan Lochbrunner 1 , and Eberhard Riedle 1
— 1 Lehrstuhl für BioMolekulare Optik, Sektion Physik, Ludwig-
Maximilians-Universität München — 2 Physics Department, Indian
Institute of Technology Madras, Chennai, India
Indole is a chromophore of many nitrogen heterocyclic biomolecules,
like the essential amino acid tryptophan. We have performed femtosecond
UV-visible broadband absorption studies of the photodynamics of
indole in different solvents and compared the results with steady state
measurements. In the nonpolar solvent cyclohexane we observe population
transfer from the optically excited La state to the Lb state within 7
ps. In the polar solvent ethanol ultrafast state reversal is found followed
by population transfer from the Lb to the La state within 6 ps. In water
efficient photoionization is observed in addition to fluorescence. Presol-
49
vated electrons are formed together with indole radicals within our time
resolution of 60 fs and are solvated further in about 350 fs. We propose
an ultrafast branching between the ionization and fluorescence channel
immediately after the optical excitation. Contrary to the case of solvated
electrons in pure water, electrons stemming from indole do neither exhibit
dielectric relaxation in the range of 1 - 2 ps nor recombination on
the 100 ps time scale.
MO 4.3 Mo 11:30 HS 315
Time-resolved spectroscopy of intramolecular excited state electron
transfer — •Thomas Schultz 1,2 , Susanne Ullrich 1 , Stefan
Lochbrunner 1,3 , and Albert Stolow 1 — 1 Steacie Institute
for Molecular Sciences, National Research Council, Ottawa, Canada —
2 Present address: Max-Born Institute for Non-linear Optics, Berlin, Germany
— 3 Present address: LS für BioMolekulare Optik, Sektion Physik,
Ludwig-Maximilians-Universität München, Germany
We used time-resolved photoelectron spectroscopy to investigate
the excited state electron transfer dynamics in a series of
aminobenzonitriles including cyanobenzene, 4-aminobenzonitrile, N,N-4dimethylaminobenzonitrile
and N,N-4-diisopropylaminobenzonitrile (DI-
ABN). This class of molecules has been extensively discussed as prototype
models for twisted intramolecular charge transfer (TICT). We found very
fast initial dynamics due to intramolecular vibrational energy redistribution
in all investigated compounds. In DIABN we additionally observed
population transfer from a locally excited to the charge transfer state.
The electron transfer rate of 0.25/ps was independent of the excitation
energy in the wavelength range 250 - 303 nm. A discrepancy between the
observed population decay in the locally excited state and the population
rise in the charge transfer signal. Possible explanations for this finding
will be discussed in detail.
MO 4.4 Mo 11:45 HS 315
Experimental verification of the ultrafast intramolecular
electron transfer in triphenylmethane lactones — •Tanja
Bizjak 1 , Jerzy Karpiuk 2 , Stefan Lochbrunner 1 , and Eberhard
Riedle 1 — 1 LS für BioMolekulare Optik, Sektion Physik, Ludwig-
Maximilians-Universität München — 2 Institute of Physical Chemistry,
Polish Academy of Sciences, Warsaw