THE SURFACE-CHEMISTRY OF METHYLENE IODIDE ADSORBED ON CLEAN AND OXYGEN-COVERED MO(100) - FORMATION AND CHEMISTRY OF CARBENES

Carbene species are grafted onto Mo(100) by the thermal decomposition of methylene iodide, where the decomposition is followed using ultravi olet photoelectron spectroscopy. Carbenes hydrogenate to methane by re action with surface hydrogen via a second-order reaction with an activ ation energy of 21 +/- 2 kJ mol(-1). Experiments with deuterium show t hat there appears to be no hydrogen-deuterium exchange between the car bene and surface hydrogen. The carbene decomposition temperature incre ases with the addition of oxygen to the surface, and this effect is as cribed to the effect of site blocking rather than a chemical modificat ion of the adsorbed carbene by coadsorbed oxygen. Similarly, although the methane desorption temperature increases with increasing oxygen co verage, this effect is found to be due to a change in the surface cove rage of carbene and hydrogen rather than a chemical modification of th e carbene itself. Finally, no ethylene or ethane are found to desorb f rom the surface. (C) 1997 Elsevier Science B.V.