Theory of Radiationless Transitions in an Isolated Molecule

A treatment of radiationless transitions in an isolated molecule is considered using a Green's-function formalism. Molecular eigenstates are constructed by superposition of quasidegenerate Born–Oppenheimer states, considering the mixing of one and two discrete zero-order BO states(s) with a manifold of quasicontinuum BO states, which correspond to another electronic configuration. The nature of inhomogeneous line broadening and the time evolution of the excited states are considered. The radiative decay following a coherent excitation process is treated in detail. The various features and anomalies observed in the decay times of medium-size and large molecules can be properly accounted for.