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MO: Molekülphysik
MO 5: Theorie I
MO 5.4: Vortrag
Montag, 22. März 2004, 14:45–15:00, HS 355
Identifying small organic molecules: A detailed experimental and theoretical study of C 1s NEXAFS spectra of C6 ring containing molecules — •C. Kolczewski1, R. Püttner2, M. Martins2, A.S. Schlachter2, G. Snell2, M. Sant’anna2, K. Hermann1, and G. Kaindl2 — 1Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany — 2Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin, Germany
High resolution, vibrationally resolved, NEXAFS spectra at the C 1s ionization threshold have been recorded for a series of small organic molecules from cyclohexene, C6H10, to the simplest aromatic molecule benzene, C6H6, with a fully delocalized π-electron system. Ab initio density functional theory (DFT) calculations have been performed to interpret the experimental spectra. Here we focus on the energetic position of the C 1s → π* transition peak in the experimental NEXAFS spectrum of 1,3 cyclohexadiene which is shifted with respect to the other molecules. Based on our theoretical studies the shift can be explained by the structure of the corresponding final state orbital. For 1,3 cyclohexadiene it is almost identical to that of cis-butadiene whereas for the remaining molecules the corresponding final state orbitals are more similar to those of benzene.
If electronic relaxation effects and an approximate vibrational fitting (based on experimental data) are included our theoretical spectra agree perfectly with experiment.