Quantum statistical mechanical (QSM) approach to molecular relaxation phenomena: An irreversible thermodynamic theory for radiationless transitions

The quantum statistical mechanical (QSM) approach to molecular relaxation phenomena is extended to allow for nonexponential decay and the incorporation of external disturbances. Microscopic models can be substituted into the final results to study the temporal evolution of multistate systems. The relationship of the present version of QSM theory to Onsager’s theory of linear irreversible processes is discussed. It is shown that kinetics and the principle of detailed balance emerge from QSM theory. The results of QSM theory are related to Fermi’s golden rule, the scattering theoretic formulation of radiationless transitions, and Kubo’s generating function technique.