15min:

VERONIKA HORKÁ, MARTIN QUACK, MARTIN WILLEKE, Laboratorium für Physikalische Chemie, ETH Zürich, CH-8093, Zürich, Switzerland.

Intramolecular vibrational energy redistribution (IVR) on the femto- to picosecond time scale is a central primary process in unimolecular chemical reaction dynamics. There are two main approaches towards its understanding. One is the analysis of the highly resolved vibrational spectra of polyatomic molecules^, combined with ab initio calculations. Another approach consists in time resolved femtosecond (fs) pump-probe experiments, which we have recently carried out for a series of alkyliodides including \mathrmCHD₂I. For the latter molecule we present here results for IVR processes within the CH-chromophore. The infrared absorption spectrum of \mathrmCHD₂I from 500 to 12000 cm^-1 has been recorded with a Bomem Fourier transform infrared spectrometer equipped with a White type multi reflection cell and resolutions of 0.10 and 0.15 cm^-1. The CH-chromophore bands dominate the vibrational overtone spectrum of \mathrmCHD₂I and we have assigned 24 of them. Vibrational variational calculations were carried out for the overtone spectrum of the CH-chromophore based on a 3-dimensional ab initio potential energy and electric dipole moment surface in normal coordinates. The anharmonic resonance structure between the CH-stretching and bending modes was investigated via an effective Hamiltonian for both experimental and theoretical spectra. Finally, we have calculated the time dependent dynamics on the fs time scale.