INVESTIGATION OF INTERNAL-CONVERSION IN CHROMYL CHLORIDE

The nature of the experimentally observed biexponential fluorescence decay from single vibronic levels of the first excited electronic state S1 of chromyl chloride [D. S. Tinti, J. S. Baskin, and A. H. Zewail, Chem. Phys. Lett. 155, 243 (1989)] was investigated theoretically on the basis of a model proposed by these authors. Through explicit computations of nonadiabatic coupling matrix elements and effective vibronic level densities, an internal conversion process was shown to occur to a sparse set of highly vibrationally excited levels, belonging to S0. The rate constant of the process was determined. This sparse set served as an intermediate state in the overall redistribution process, decaying subsequently [through intramolecular vibrational energy redistribution (IVR)] into the dense set of vibrational levels from S0. Analysis showed that the sparse set was characterized by extremely high (strongly nonequilibrium) excitation of Cr-O stretch vibrational character. The computations are consistent with the model proposed by Tinti et al. for rationalizing the fluorescence characteristics of S1 chromyl chloride.