RADIATIVE DECAY OF POLYATOMIC MOLECULES

In this paper we present a quantum-mechanical treatment of the radiative decay of polyatomic molecules. The decay of a manifold of closely spaced coupled levels is handled by applying the Green's function formalism for the transition probability, where the matrix elements are displayed in an energy representation which involves either the Born-Oppenheimer or the molecular eigenstate basis set. General criteria are obtained for the occurrence of an irreversible intramolecular electronic relaxation process. The features of radiationless transitions in large, medium-sized, and small molecules are elucidated, deriving general expressions for the radiative decay times and for the fluorescence quantum yields. Some possibilities for studying radiative interference effects in intersystem crossing are explored. A general theoretical demonstration of the occurrence of long radiative lifetimes of small molecules is presented.