THE COUPLING BETWEEN ADSORPTION DYNAMICS AND THE SURFACE-STRUCTURE - H-2 ON SI(100)

We provide direct theoretical evidence for the existence of a strong coupling between the barrier for H2 dissociation and the structure of the Si(100) surface. Our arguments are based on an ab initio calculation of the potential energy surface for the dissociation process. While adsorption on the buckled dimers, which make up the surface ground state, is found to be activated by 0.67 eV, exciting the dimers to a less buckled configuration lowers the barrier considerably. We argue that such a coupling is the key to resolve the apparent inconsistencies between desorption and sticking experiments and present a model calculation of its consequences for the variation of the adsorption probability with surface temperature. We can account quantitatively for the recently observed thermally activated sticking of H2 on this surface.