Frankfurt 2006 – scientific programme

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MO: Molekülphysik

MO 14: Ultrafast IR and Raman Probe and Control

MO 14.2: Talk

Monday, March 13, 2006, 16:45–17:00, H12

Ultrafast vibrational relaxation of the O–H bending mode in liquid H₂O — •Satoshi Ashihara, Nils Huse, Erik T. J. Nibbering, and Thomas Elsaesser — Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489 Berlin, Germany

The mechanisms of vibrational energy transfer in liquid water are essential for the understanding of its physical and chemical properties. The dynamics of the O–H stretching vibrations in water have been intensively studied in recent years but much less is known about the dynamics of the O–H bending mode. This mode is highly relevant for the geometry of the intermolecular hydrogen bonds and for the relaxation of O–H stretching excitations. Here we study the population relaxation of the O–H bending mode in pure liquid H₂O in mid-infrared pump-probe experiments with 100 fs time resolution [1]. After resonant excitation of the v = 0 to 1 bending transition, a v = 1 lifetime of 170 fs is measured. This short lifetime is determined by the anharmonic couplings to the fluctuating liquid environment forming an extended hydrogen bond network. The population relaxation is followed by slower spectral diffusion and energy redistribution processes within 1-2 ps. Femtosecond excitation also induces ultrafast nonlinear changes of the broad librational absorption occurring at frequencies below the v = 0 to 1 bending transition.

[1] N. Huse, S. Ashihara, E.T.J. Nibbering, T. Elsaesser, Chem. Phys. Lett. 404 (2005) 389.