Some theoretical results for the photochemical decomposition of large molecules

The expressions describing photochemical dissociation derived by Rice, McLaughlin, and Jortner are evaluated analytically for molecules satisfying Γ≫(l+r) and for times t≪h/ε, where T is the width of the initial state due to interaction with an intermediate manifold, ε is the level spacing of the manifold, and r is essentially the ratio of the manifold level widths to ε. Excitation is found to decay exponentially from the initial state with rate Γ/[ (1+r)h]. In contrast to the behavior originally perdicted, the decay is found to be nonsequential, and a constant ratio, equal to r, is maintained between the populations of the continuum and the manifold. The results should be applicable to large molecules having a single decomposition mode.