The dynamics of H2 dissociation on Ni(100): A quantum mechanical study of a restricted two-dimensional model

Abstract

A quantum mechanical study of the dynamics of H2 dissociation on Ni is presented. The H2 molecule approaches the surface and is held parallel to the surface. The center of mass is atop a Ni atom and the dissociated atoms have minimum energy at bridge binding sites. This restricted molecular configuration allows us to propagate the molecular wave function in time numerically, using fast Fourier transform techniques. The probability for dissociative adsorption is computed as a function of initial molecular kinetic energy, for a variety of model gas–surface potentials. The way in which the height of the barrier to dissociation affects this energy dependence, as well as the nature of the transfer of energy from the center of mass into the relative motion of the H atoms is examined. By including effects due to H atom mobility it is demonstrated how barriers to surface diffusion can dominate dissociation rates by controlling the extent of recombination. Activation barriers to adsorption in the entrance channel are shown to attenuate the incoming molecular beam, and temporarily trap H2 near the surface. The dissociation of H2 is fairly nonclassical, particularly at thermal energies where much reflection occurs at barrier crossing even when the incident energy is above the barrier.