Hannover 2013 – scientific programme

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MO: Fachverband Molekülphysik

MO 19: Poster 2: Biomolecules, Cold Molecules, Experimental Techniques, Various Topics

MO 19.1: Poster

Wednesday, March 20, 2013, 16:00–18:30, Empore Lichthof

Fluorescence spectroscopy of isolated PTCDA molecules on the KCl surface: Site selection and vibrational spectra — •Alexander Paulheim, Mathias Müller, Christian Marquardt, and Moritz Sokolowski — Institute for Physical Chemistry, University of Bonn, Wegelerstraße 12, 53115 Bonn, Germany

We performed fluorescence and fluorescence excitation spectroscopy on the model molecule perylene-3,4,9,10-tetracarboxyl acid dianhydride (PTCDA) for very low coverages (below 1% of a monolayer) on thin (100)-oriented KCl films. Two different states of PTCDA molecules can be distinguished in the spectra: an initial state which is observed directly after deposition onto the cold sample, and a final state which is found after thermal annealing or intensive optical excitation. The spectrum of the final state is blue-shifted with respect to that of the initial state by 130 cm⁻¹ and exhibits a smaller FWHM due to reduced inhomogeneous site broadening. This can be explained by a thermally or optically induced diffusion of the PTCDA molecules from initial terrace sites to energetically favored step edge sites. In addition, we analyzed the vibronic modes in detail. This analysis reveals that the bonding of the molecule to the surface results in additional vibrational modes which are caused by a reduction of the molecular symmetry.