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MO: Molekülphysik

MO 42: Excitation and Coherence Decay

MO 42.6: Talk

Wednesday, March 15, 2006, 15:15–15:30, H12

Ultrafast proton transfer and vibrational coherence in the gas phase — •Christian Schriever, Stefan Lochbrunner, and Eberhard Riedle — LS für BioMolekulare Optik, Ludwig-Maximilians-Universität München

The ultrafast excited state intramolecular proton transfer (ESIPT) is a prototype photoinduced chemical reaction that strongly couples electronic and nuclear motion. It has recently been studied by means of transient absorption measurements with sub-30-fs resolution. From these measurements a novel model of the ESIPT mechanism was derived that emphasizes the importance of the slow skeletal modes [1]. Typically, the wavepackets that are observed in the keto form after the ESIPT dephase on a time scale of 1 ps. It is not yet known whether this dephasing is mainly due to intramolecular vibrational coupling or due to the influence of the solvent. Neither is it known, whether the ESIPT and its irreversible nature depend on the solvent for a given molecule. We will decide these questions by comparison of the solution phase and the gas phase ultrafast behavior. The measurement in the gas phase is quite challenging due to the low vapor pressure that necessitates a collinear pump probe arrangement with matching of the beam sizes over a long range. To maximize the transient signal, we have recorded time resolved spectra from 310 to 700 nm. These reveal very large absorptions in the near UV that render a fivefold larger signal than the stimulated emission in the visible.

[1] S. Lochbrunner, A. J. Wurzer, and E. Riedle J.Phys.Chem. A 107, 10580 (2003)