Adsorption and Dissociation ofH2on Mg Surfaces

A self-consistent calculation of the potential-energy surface for a molecule (${\mathrm{H}}_{2}$) on a metal surface [Mg(0001)] is presented. The following experimentally observable adsorption features are identified and interpreted: (i) an activation barrier for molecular adsorption, (ii) a mobile molecularly chemisorbed state ("precursor state"), (iii) an activation barrier for dissociation (${{E}_{a}}^{d}$), and (iv) a strong dependence of ${{E}_{a}}^{d}$ on the adsorption-site geometry.