Theoretical studies of surface reactions on metals: I. Ethyl to ethylene conversion on platinum; II. Photodissociation of methane on platinum

An embedding method designed to provide a molecular level understanding Of adsorbate energetics and surface reaction mechanisms is presented. Electron ic structures; including relativistic effects, are described by an ab initi o formalism that permits an accurate determination of energies and adsorbat e structure. Applications to catalytic and photochemical reactions on trans ition metal surfaces are reported. (I) In the catalytic conversion of ethyl adsorbed on platinum surfaces to ethylene, the minimum energy pathway for the transfer of hydrogen to the metal surface is calculated. A detailed des cription of the transition state is presented. (II) In the photodissociatio n of methane physisorbed on platinum, results are reported for a methane mo lecule interacting with an embedded cluster model of Pt(111). Configuration interaction theory is: used to-sort out states resulting from electron att achment to methane from lower energy states that correspond to metal. excit ations. Energies of the ground and excited states of the Pt(111)CH4 complex are calculated as a function of geometrical distortions and the distance o f methane from the-surface. Key steps in the photodissociation process are described. (C) 1999 American Vacuum Society. [S0734-2101(99)15704-X].