Photodissociation dynamics of the Kr-HBr cluster: the effect of the rare gas atom substitution.

The ultraviolet photolysis dynamics of Kr-HBr(v=0) is investigated by means of wave packet calculations, focusing on the fragmentation pathway Kr-HBr+ variant Planck's over 2pi omega-->H+Kr-Br. Photolysis is simulated by starting from two different cluster initial states, namely the ground van der Waals (vdW) and an excited vdW bending state, associated with the Kr-H-Br and Kr-Br-H isomers, respectively. The results show that, for the two initial states of the cluster, the Kr-Br product yield is lower than that of Ar-Br radicals found in previous studies on Ar-HBr photolysis. Despite this decrease, the Kr-Br yield is found to be still rather high, in particular for the initial excited vdW state of Kr-HBr(v=0). In addition, the Kr-Br product state distributions exhibit a remarkably higher excitation (mainly rotational) than the corresponding Ar-Br distributions. The lower yield and higher excitation of Kr-Br as compared to Ar-Br, are attributed to a larger share of the energy available for the radical going to internal excitation in the case of the Kr-Br product. The different partition of the energy available for Kr-Br also causes significant deviations in the photolysis behavior of Kr-HBr when compared to that of Ar-HBr, in the case of the initial excited vdW state of both clusters. A common feature of the photodissociation of Kr-HBr and Ar-HBr is the manifestation of quantum interference effects in the Kr-Br and Ar-Br rotational state distributions, in the form of pronounced structures of supernumerary rotational rainbows.