Deutsche Tagung f ¨ur Forschung mit ... - SNI-Portal

Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P286
Solid state and isotope effects in high–resolution NEXAFS spectra of large
organic molecules
Florian Holch 1 , Dominique Hübner 1 , Achim Schöll 1 , Rainer Fink 2 , Eberhard
Umbach 1
1 Universität Würzburg, Experimentelle Physik II – 2 Universität Erlangen, Physikalis-
che Chemie II
The interaction between most large organic molecules in the solid state is commonly
believed to be solely due to electrostatic and van–der–Waals forces. An analysis of
these intermolecular effects requires a comparison of high–quality spectroscopic data of
gaseous and condensed organic molecules. We present high–resolution NEXAFS spectra
of organic molecules with aromatic ring systems (naphthalene, NTCDA (1,4,5,8–
naphthalene–tetracarboxylic acid dianhydride) and ANQ (acenaphthenequinone)) in
the gas phase and solid state.
For the NTCDA and ANQ gas phase experiments a new experimental set–up has been
used that allows the measurement of free molecules with high sublimation temperatures.
A detailed Franck–Condon analysis of the vibronic fine structure of the NTCDA
spectra at the C–K edge yields consistent results for both phases. In contrast, pronounced
differences in the electronic features between gas phase and condensate can be
demonstrated. This corroborates the results for ANQ that also suggest an involvement
of the π ∗ –orbitals of the aromatic core in the intermolecular interaction. Our findings
thus indicate that intermolecular forces can be much stronger than commonly believed
and may cause the formation of intermolecular bonds.
Moreover, we will present results of NEXAFS investigations on naphthalene and fully
deuterated naphthalene in the gas phase [1]. The differences in the spectroscopic signatures
of the two isotopes strongly suggest significant contributions of C–H (C–D)
and C–C vibrational modes in contrast to theoretical results [2]. This is corroborated
by a comparison with similar spectra of (deuterated) benzene, which allows the identification
of at least two C–H (C–D) modes and one C–C mode.
This work has been financially supported by the BMBF (projects 05KS4WWC/2,
05SF8WWA7 and 05KS1WWA5). Traveling benefits to perform the experiments at
ELETTRA were provided by the EU through the VI Framework program for transnational
access, under Contract No. RII3-CT-2004-506008 (IA-SFS).
[1] D. Hübner et al., Chem. Phys. Lett. 415 (2005) 188
[2] I. Minkov et al., J. Chem. Phys. 121 (2004) 5733