Hannover 2010 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 4: Spectroscopy in He droplets

MO 4.4: Vortrag

Montag, 8. März 2010, 17:30–17:45, F 142

Electronic Spectroscopy of Anthracenes in superfluid helium droplets II: broadening of spectra — •Dominik Pentlehner, Christian Greil, Bernhard Dick, and Alkwin Slenczka — Universität Regensburg, Institut für Physikalische und Theoretische Chemie, 93053 Regensburg, Germany

Superfluid helium droplets are a favored cryogenic matrix due to a low temperature of only 0.37 K and its gentle interaction with dopants. Under these conditions, electronic spectra of rigid molecules like planar aromatic molecules use to show very sharp transitions. Though, electronic spectra of some organic molecules exhibit a broadening of zero phonon lines compared to the corresponding gas phase spectra.

The electronic spectra of anthracenes with a methyl or phenyl substituent will be discussed with particular emphasis on low frequency vibrational modes (torsions). In the case of extended Franck-Condon progressions in these modes, which indicate that a conformational change is induced by the electronic excitation, extensive line broadening appeared. For short Franck-Condon progressions the transitions remain sharp. We propose a model to explain the broadening by an enhanced dissipation of vibrational energy into the droplet leading to a homogeneous broadening of transitions. From the linewidth we estimate the time constant for the energy dissipation to be about 0.2 ps in the case of 9-Phenylanthracene and 0.5 ps for 2-Methylanthrace.