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MO: Fachverband Molekülphysik

MO 52: Femtosecond Spectroscopy IV

MO 52.3: Vortrag

Donnerstag, 22. März 2007, 14:30–14:45, 6B

Mode-selective vibrational energy transfer after infrared excitation of a hydrogen-bonded OH stretching vibration — •Valeri Kozich, Wolfgang Werncke, Jens Dreyer, Satoshi Ashihara, and Thomas Elsaesser — Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Strasse 2A, D-12489 Berlin, Germany

Vibrational energy relaxation in hydrogen bonds is of considerable importance for understanding ultrafast dynamics in many chemical and biological systems. We have studied the relaxation of the hydrogen-bonded OH stretching vibration of 2-(2'-hydroxy-5'-methyl-phenyl)benzotriazole (TINUVIN P) by ultrafast infrared-pump/Raman probe and infrared-pump/infrared probe spectroscopy. We determined a 200 fs lifetime for the OH stretching mode and revealed that intramolecular vibrational energy redistribution occurs through a few major channels that all involve combination and overtone bands of modes with considerable in-plane OH bending character. The most prominent role for the primary relaxation process is played by the mode with the largest OH bending contribution, thus highlighting the important role of energy transfer from stretching to bending motions in hydrogen bonds. Theoretical calculations of vibrational energy transfer rates based on a Fermi golden rule approach are in accordance with these experimental results.