Angular and vibrational effects in the sticking and scattering of H2

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Abstract
The results of quantum mechanical simulations of H2 dissociation on metal surfaces are presented using an extension of the familiar two‐dimensional ‘‘elbow’’ potential. By including corrugation parallel to the surface, it has been possible to examine the effects on the angular and energy distributions of dissociative adsorption and scattering. Additionally, trends obtained by moving the activation barrier from entrance to exit channel have been studied. To effect a closer analogy with experiment, seeding of the incident beam has been simulated by Boltzmann weighting dissociation probabilities. It is particularly important to include the experimental spread of the incident translational energy in calculations. It is found that for hydrogen dissociation on Cu and Fe, dissociative adsorption results can only be reconciled with a late barrier, while for Ni and Pd it appears to be early. For the scattered fraction, the late barrier gives rise to a significant enhancement in the diffraction of vibrationally excited molecules. This is explained in terms of the corrugation of the vibrationally adiabatic potential energy surfaces.