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 $\text{Γ ≫ ε (1+r)}$ and for times $\mathrm{t\; \ll \; \hslash \; /\; \epsilon }$ , where $\Gamma$ 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 $\text{Γ / [(1+r) ℏ]}$ . 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.