Friedrich Temps

Institut fuer Physikalische Chemie, Christian-Albrechts-Universitaet zu Kiel, Olshausenstr. 40, D-24098 Kiel, GERMANY

Stimulated Emission Pumping (SEP) spectra have provided detailed information on the vibrational structure and the state-specific unimolecular decay constants of DCO (X) up to energies of E_v = 18200 cm^-1, far above the asymptotic D-CO dissociation limit at 5400 cm^-1 [1].  The available experimental data were used to develop a simple effective polyad model Hamiltonian for the system which was applied to rationalize the observed unimolecular dynamics.  The parameters occuring in the model were determined by fitting to the measured vibrational bound and resonance state energies up to Ev = 15000 cm^-1. The vibrational states predicted by the model were found to be in excellent agreement with the experimental data and with data from published quantum dynamics work [2].  Based on the fitting results, the rates and pathways were investigated for intramolecular vibrational energy redistribution (IVR) in the highly excited DCO (X).  Decay constants could be predicted for the progressions of excited local mode CO stretching overtone states and excited DCO bending overtone states.  The results of these calculations show a mode specificity which reflects the different strengths of the couplings between the internal coordinates and explains the observed large discrepancies between the decay constants from the SEP measurements and the statistical rate theory calculations. Using a complex version of the model Hamiltonian, state specific decay constants could be calculated for the individual eigenstates near the threshold of the reaction which reflect the coarse experimental trends.

[1]  Stoeck et al., J. Chem. Phys.106, 5333 (1997).
[2]  Schinke et al., J. Chem. Phys. 106, 5359 (1997).