Dresden 2003 – scientific programme

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O: Oberflächenphysik

O 4: Elektronische Struktur I

O 4.4: Talk

Monday, March 24, 2003, 12:00–12:15, FOE/ANOR

Electron-vibron coupling in core excitations of organic molecules — •Achim Schöll¹, M.L.M. Rocco², Y. Zou¹, D. Hübner¹, Th. Schmidt¹, R. Fink³, and E. Umbach¹ — ¹Experimentelle Physik II, Universität Würzburg, Am Hubland, 97074 Würzburg — ²Instituto de Quimica,Universidade Federal de Rio de Janeiro, 21949-900, Ilha do Fundao, Rio de Janeiro, RJ, Brazil — ³Universität Erlangen-Nürnberg, Physikalische Chemie II, Egerlandstrasse 3, 91058 Erlangen

The ultrahigh resolution of third-generation, high-brilliance synchrotron beamlines allows us to observe a wealth of new fine structures in the near-edge x-ray absorption spectra of thin films of condensed organic molecules. The now visible coupling of electronic transitions to vibronic excitations yields information on the localization of the electronic system. We report on a recent high-resolution C-K and O-K NEXAFS study on the similar molecules NTCDA, NDCA, BPDCA and ANQ, consisting of ring systems of different size with either anhydride or quinoidic functional groups, as well as on Antracene and Tetracene. The spectra show very distinct differences in the electron-vibronic coupling; e.g. for some molecules vibronic coupling is only visible for C-K, for others only for O-K excitation. The data are very sensitive to the molecular structure and the geometric order within the film. Backed by ab-initio calculations we discuss these differences in terms of the localization of the core hole and of the molecular π-system. (Förderung durch das BMBF, Fkz. 05 KS1WWA 5)