Orbiting resonance model for recombination of physisorbed atoms

The orbiting resonance model for atomic recombination, originally developed for applications to gas phase kinetics, is adapted for describing the recombination of atoms physisorbed on a surface. The model assumes that a population of atoms is initially physisorbed on a surface on which the atoms are free to move about in two dimensions. Atom-atom collisions give rise to long-lived orbiting pairs, which may in turn lose internal energy and become truly bound. The surface lowers the dimensionality of the problem, plays the role of the third body whose participation preserves energy and momentum conservation, and its corrugation provides the perturbation driving the second (inelastic) step of the mechanism. The present work involves the application of this model to the recombination of H or D atoms on the (111) and (100) surfaces of a Xe crystal, to obtain overall second-order rate constants at T=4 and 10 K.