Hamburg 2009 – scientific programme

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MO: Fachverband Molekülphysik

MO 19: Spektroskopie in He-Tröpfchen

MO 19.3: Talk

Thursday, March 5, 2009, 14:45–15:00, VMP 6 HS-F

Electronic Spectroscopy of Pyrromethene Dyes in Superfluid Helium Droplets — •Dominik Pentlehner, Anja Stromeck-Faderl, Bernhard Dick, and Alkwin Slenczka — Universität Regensburg, Institut für Physikalische und Theoretische Chemie, 93053 Regensburg, Germany

Among the vibrational modes of pyrromethene (PM) dyes the low-frequency modes are a significant spectroscopic signature. Electronic spectra of gas phase samples show low frequency progressions which depend on the substituents such as methyl or phenyl. These low-frequency modes are sensitive to interactions with the environment and thus are suited to study the helium-dopant interaction in superfluid helium droplets. Our project aims for a better understanding of this interaction which allows for both, a highly efficient dopant to helium energy dissipation, but also for free dopant rotation. Therefore, we have measured fluorescence excitation spectra and dispersed emission spectra of various PM dyes in the gas phase as well as in helium droplets, which are generated by a pulsed Even-Lavie valve.

In contrast to most electronic spectra of molecules embedded into helium droplets, the spectra of some of the PM dyes in helium droplets deviate from the respective gas phase data by substantial broadening or even missing of vibronic transitions. Our data reveal a correlation between the presence of low energy modes in the gas phase and the line broadening effect in helium droplets.