EXPERIMENTAL STUDIES OF RESONANCES IN UNIMOLECULAR DECOMPOSITION

In recent years we have witnessed tremendous progress in our understan ding of unimolecular reactions on a fully state-resolved level. Here w e describe recent state-resolved experimental studies of resonances in unimolecular reactions, focusing on the transition from isolated to o verlapping resonances. Depending on th, well depth and extent of intra molecular vibrational energy redistribution, the resonances can exhibi t properties ranging from mode- and state-selective to statistical beh avior. In the statistical limit the resonances are usually overlapped, and interference effects may become prominent. We use recent studies of HCO, HFCO, and CH3O to examine the transition from mode-selective t o statistical behavior in the isolated regime. Experimental and theore tical studies of NO2, including photofragment yield spectra, fully res olved NO quantum state distributions, and decomposition rates are used to examine unimolecular decomposition in the regime of overlapping re sonances.