München 2004 – scientific programme

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MO: Molekülphysik

MO 10: Femtosekundenspektroskopie: Schwingungsdynamik

MO 10.1: Talk

Monday, March 22, 2004, 16:30–16:45, HS 315

IR versus Raman Spectroscopy: Monitoring Vibrational Cooling after Electronic Excitation — •Arne Sieg, Tobias Schrader, Florian Koller, Wolfgang Schreier, Qingrui An, and Peter Gilch — Sektion Physik, Ludwig-Maximilians-Universität, Oettingenstr. 67, D-80538 München, Germany

Molecules undergoing ultrafast (∼ 100 fs) internal conversion processes (IC) are very suitable model systems for the examination of the vibrational dynamics related with chemical reactions. The detection of these dynamics can be performed by time resolved IR and Raman spectroscopy. In a combined study on the vibrational cooling of para-nitroaniline (pNA) both methods are compared. Only Raman spectroscopy gives access to the excitation of a stretch mode, which is shown to decay in ∼ 3 ps [1]. IR spectroscopy is better suited to monitor the frequency shift of this resonance. This shift to lower wavenumbers relaxes with time constants of 1 – 11 ps. It stems from anharmonic coupling to other vibrational modes. Therefore, this shift is an useful sensor for the population and dynamics of these low frequency modes. [1] Q. An, P. Gilch, Chem. Phys. Lett. 363 (2002) 397