Stereodynamics and control effects in the ultraviolet photolysis of Ar–HBr

Abstract

The ultraviolet photolysis of the Ar–HBr cluster is studied by means of quasiclassical trajectory simulations. The goal is to investigate the effect of the initial distribution of intracluster orientations on the photolysis process. Cluster photolysis is simulated starting from two different initial states of Ar–HBr(v=1), namely the ground and the first excited van der Waals states corresponding to the Ar–H–Br and Ar–Br–H isomers, respectively. These two states represent different initial situations for hydrogen dissociation, which in the first case is hindered to a large extent, and in the second case is not. The probability for the fragmentation pathway into H and Ar–Br radical fragments is found to be substantially higher (and therefore the efficiency of the total fragmentation pathway, into H+Ar+Br, is lower) for the cluster initial state where H dissociation is less hindered. The effect of the angular distributions shape of the initial state is also clearly manifested in the state distributions of the different photofragments. It is concluded that selecting the initial state of the cluster on the basis of the shape of its angular distribution provides an efficient means to control the yield of the different fragmentation pathways, and the final states of their corresponding photolysis products.