Weak interactions and photoinitiated unimolecular decomposition

Numerical studies have been carried out to examine the applicability of the density of states measured just below dissociation threshold to transition state rate theory. The model system consists of two weakly interacting manifolds of levels, one of which is optically accessible. Both manifolds are coupled to dissociative continua. These studies demonstrate that immediately above reaction threshold, coupling to continua is relatively slow on the time scale of inter-manifold coupling, and it is the mixed manifolds which decay. At higher energies, couplings to continua exceed inter-manifold couplings, and it is the photoexcited bright states which undergo unimolecular decomposition.