Photodissociation of the SO2⋅SO+2 dimer in the visible region of the spectrum: Product relative kinetic energy distributions and product angular distributions

Abstract

The results of an investigation of the photodissociation of the SO2⋅SO+2 cluster ion in the visible wavelength range (458–590 nm) are presented. The studies were performed using a crossed fast ion beam/laser beam experiment. Product relative kinetic energy distributions and product center of mass angular distributions are reported. Methods used to extract the angular distributions from the experimental measurements are described. The only ionic product observed from the photodissociation of SO2⋅SO+2 was SO+2. The product relative kinetic energy distributions are characteristic of statistical energy disposal. However, statistical phase space theory substantially overestimates the fraction of available energy partitioned into relative kinetic energy. The product angular distributions are discussed in terms of the asymmetry parameter β. β increases with the products relative velocity. A simple phase space theory model for β is developed for statistical dissociation with complete rotational averaging. The model accounts for the variation of β with the products relative velocity. β also varies with wavelength. The variation of β with wavelength is ascribed to changes in the lifetime of the cluster. At 458 nm the values of β indicate that complete rotational averaging has not occurred. At 590 nm the data are consistent with complete rotational averaging, implying a lifetime>5 average rotational periods. The results are interpreted in terms of a transition to a low lying bound excited state of the SO2⋅SO+2 cluster which arises from one of the low lying excited states of SO+2 and the ground state of SO2.