Molecular Orientation Dependence of Dynamical Processes on Metal Surfaces: Dissociative Adsorption and Scattering, and Associative Desorption of Hydrogen

Abstract

The effect of molecular rotational motion on such dynamical processes as dissociative adsorption and associative desorption of hydrogen molecules on metal surfaces is presented in the first half. It is shown that two effects, viz.,steering effect, and R-T (rotational-translational) energy transfer effect, which originate from the molecular rotational degrees of freedom, give rise to a non-monotonous behavior of the adsorption probability of H2(D2)/Cu(111) as a function of its initial rotational state when it undergoes dissociative adsorption. It is also shown that a very prominent initial cooling, a mild heating, and then a final cooling of the rotational temperature with respect to the surface temperature, for increasing rotational energies, is observed for the desorption of H2(D2) from Cu(111). In the second half, the dissociative scattering of hydrogen molecules from metal surfaces is used as a representative dynamical process occurring on surfaces in the hyperthermal beam energy region to show how molecular orientation dependence manifests itself.