Formation of novel rare-gas-containing molecules by molecular photodissociation in clusters

Recent work by Rasanen and coworkers showed that photolysis of hydrides in rare-gas matrices results in part in formation of novel, rare-gas-containin g molecules. Thus, photolysis of HCl in Xe and of H2O in Xe result respecti vely in formation of HXeCl and HXeOH in the Xe matrices. Ab initio calculat ions show that the compounds HRgY so formed are stable in isolation, and th at by the strength and nature of the bonding these are molecules, very diff erent from the corresponding weakly bound clusters Rg . . . HY. This paper presents a study of the formation mechanism of HRgY following the photolysi s of HY in clusters Rg(n)(HY). Calculations are described for HXeCl, as a r epresentative example. Potential energy surfaces that govern the formation of HXeCl in the photolysis of HCl in xenon clusters are obtained, and the d ynamics on these surfaces is analyzed, partly with insight from trajectorie s of molecular dynamics simulations. The potential surfaces are obtained by a new variant of the DIM (diatomics in molecules) and DIIS (diatomics in i onic systems) models. Non-adiabatic couplings are also obtained. The main r esults are : (1) Properties of HXeCl predicted by the DIM-DIIS model are in reasonable accord with results of ab initio calculations. (2) The potentia l along the isomerization path HXeCl --> Xe . . . HCl predicted by DIM is i n semiquantitative accord with the ab initio results. (3) Surface-hopping m olecular dynamics simulations of the process in clusters, with "on the fly" calculations of the DIM-DIIS potentials and non-adiabatic couplings are co mputationally feasible. (4) Formation of HXeCl, following photolysis of HCl in Xe-54(HCl), requires cage-exit of the H atom as a precondition. The H a tom and the Cl can then attack the same Xe atom on opposite sides, leading to charge transfer and production of the ionic HXeCl. (5) Non-adiabatic pro cesses play an important role, both in the reagent configurations, and at t he charge-transfer stage. The results open the way to predictions of the fo rmation of new HRgY species.