Photodissociation and caging of HBr and HI molecules on the surface of large rare gas clusters

Photodissociation experiments were carried out at a wavelength of 243 nm fo r single HBr and HI molecules adsorbed on the surface of large and clusters . The Ne-n, Ar-n, Kr-n Xe-n average size is about <n> = 130; the size range s <n> = 62-139 for the system HBr-Ar-n and <n> = 110-830 for HI-Xe-n were c overed. In this way the dependence of the photodissociation dynamics on bot h the size and the rare gas host cluster was investigated. The main observa ble is the kinetic energy distribution of the outgoing H atoms. The key res ults are that we do not find any size dependence for either system but that we observe a strong dependence on the rare gas clusters. All systems exhib it H atoms with no energy loss that indicate direct cage exit and those wit h nearly zero energy that are an indication of complete caging. The intensi ty ratio of caged to uncaged H atoms is largest for Ne-n decreases with inc reasing mass of the cage atoms, and is weakest for Xe-n. On the basis of ac companying calculations this behaviour is attributed to the large amplitude motion of the light H atom. This leads to direct cage exit and penetration of the atom through the cluster with different energy transfer per collisi on depending on the rare gas atoms. The differences between HBr and HI mole cules are attributed to different surface states, a flat and an encapsulate d site.