Some Comments on a Formal Theory of Photochemical Dissociation Reactions

Abstract

In this paper we present a formal theory of photochemical fragmentation reactions for the case that intramolecular energy transfer is of importance. The zero‐order spectrum of the molecule is assumed to consist of a discrete level in resonance with a dense set of levels belonging to another electric manifold, which in turn is in resonance with a translational continuum representing molecular fragmentation. The exact eigenstates of the system are computed formally and shown to be resonant scattering states. Explicit formulas are derived for the probability of the system being in a nonstationary state represented by a wave packet localized in the discrete state, or the dense set of states resonant with the discrete state. In the case that the resonant scattering state may be approximated by a quasistationary bound state, an explicit formula relating the rate of unimolecular photochemical decomposition to the coupling matrix elements and densities of eigenstates of the system is derived. The general relationship between translational motion and internal molecular motion is discussed, as are some aspects of the dissociative decay process, the nature of the excited states, and the possible role of interference phenomena involving coherently excited states.