Dresden 2003 – wissenschaftliches Programm

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CPP: Chemische Physik und Polymerphysik

CPP 3: Biomoleküle

CPP 3.11: Vortrag

Montag, 24. März 2003, 12:45–13:00, ZEU/118

Ultrafast coherent vibrational response of hydrogen bonded complexes studied by mid-infrared spectroscopy — •Karsten Heyne, Nils Huse, Erik T. J. Nibbering, and Thomas Elsaesser — Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Str. 2A, 12489 Berlin, Germany

Cyclic dimers of carboxylic acids are important model systems forming coupled intermolecular hydrogen bonds. We investigated the vibrational motions and underlying microscopic couplings in cyclic acetic acid dimers by time-resolved pump-probe experiments in the mid-infrared. Femtosecond excitation of the OH (OD) stretching mode, induces oscillatory modulations of the pump-probe signal due to coherent nuclear motions along low-frequency modes of the dimer, persisting for several picoseconds. We assign such vibrations with frequencies of 50 cm⁻¹, 145 cm⁻¹ and 170 cm⁻¹ to an in plane counter rotation and to dimer stretching vibrations in the OH stretching mode ground and excited state. Comparative measurements on mixed dimers show that the anharmonic coupling of the OH stretching and the low frequency mode is isolated in the nonlinear vibrational response, whereas resonant splitting (davydov coupling) is suppressed.