Photodissociation and vibrational relaxation of OClO at liquid surfaces

The photodissociation dynamics of OClO to O + ClO on the (2)A(2) excited state and the vibrational relaxation of OClO in the ground electronic state at the interface of several polar liquids are studied using classical molecular dynamics computer simulations. The results are compared with recent calculations and experiments of photodissociation and vibrational relaxation of OClO in bulk water, acetonitrile, and ethanol. In contrast with substantial geminate recombination in the bulk, the photodissociation at the liquid/vapor interface of all three liquids gives rise to nearly 100% cage escape. In most of the trajectories at least one of the dissociation fragments desorb, although a significant percentage of the ClO fragments remain adsorbed at the interface. The reduced density at the interface gives rise to reduced friction and to slower vibrational relaxation of ground-state OClO (which may form as a result of geminate recombination of the photofragments). The vibrational relaxation of ground-state OClO is slower at the interface than in the bulk by a factor of 2-4, depending on the solvent and the excitation energy.