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MO: Molekülphysik

MO 14: Femtosekundenspektroskopie V: molekulare Schwingungen

MO 14.2: Talk

Thursday, March 7, 2002, 14:15–14:30, HS 15/E07

Predissociation and Vibrational Energy Relaxation of the I₂ B-state in a Kr-matrix — •Markus Gühr¹, Matias Bargheer¹, Peter Dietrich², and Nikolaus Schwentner¹ — ¹Institut für Experimentalphysik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin — ²803-1000 Castle Hill Cres., Ottawa ON, K2C 3L7, Canada

I₂ B-state predissociation in high pressure rare gas environments at 300 K was studied by the group of A. Zewail and an increase of predissociation with higher rare gas density was found. In contrast, we observe a decrease of predissociation in even more dense low temperature cryogenic-matrices by a factor of twenty compared to the high pressure rates of Zewail. In our experiment, we monitor the vibrational wave-packets by fs-pump-probe spectroscopy. We observe an exponential decrease of the vibrational relaxation rate k_vib(E) with E [1], where E is the energy above the B- state crossing with a predissociation state. In contrast, the predissociation rate k_p(E) rises in going to lower energy (Nakamura, Landau-Zener). In our modell, energy relaxation transfers population down to energy regions, where k_p gets bigger. Predissociation predominantly occurs at energies, where k_p=k_vib. This actual k_p is determined experimentally by probing the predissociated population dynamics. An increase of the actual k_p at higher matrix temperature reflects the corresponding rise in k_vib in agreement with the modell. The modell resolves the case and provides a general sceme for predissociation in dense media.

[1] M.Bargheer, M. Gühr, P. Dietrich and N. Schwentner, PCCP in print