Charge flow and solvent dynamics in the photodissociation of solvated molecular ions

We survey recent experimental and theoretical studies of photodissociation and recombination of dihalide ions in gas-phase clusters and liquid solutio n. A crucial property of these systems is the flow of excess charge within the solute, which is strongly coupled to the motion of the surrounding mole cules. Using a model inspired by the theory of electron-transfer reactions, we have constructed a comprehensive physical picture of the interplay of c harge flow and solvent dynamics on multiple, coupled electronic states. The consequences are sometimes surprising: for example, in excited states havi ng antibonding character, the charge moves to the less solvated atom as the solute dissociates, leading to more efficient recombination than in neutra l systems. Our analysis also predicts extremely efficient spin-orbit quench ing (associated with solvent-induced curve crossings) following UV excitati on of I-2(-) clustered with CO2, which has been confirmed by experiment and suggests a revised interpretation of the transient absorption peak seen in pump-probe experiments.