CHEMICALLY DRIVEN MOLECULAR DECOMPOSITION AT SEMICONDUCTOR SURFACES

We present an analysis of the chemistry of dissociative adsorption bas ed on an ab initio molecular dynamics simulation of Cl2 incident on Si (111)-2x1 at an energy of 1 eV. It is shown that the break-up of the m olecule occurs because of charge transfer into a more antibonding mole cular orbital. The process is strongly orientationally dependent and i s absent if the molecule is oriented perpendicular to the surface. In this case the molecule enters a precursor state and subsequently disso ciates when it escapes from the local energy minimum.