surface science 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 fmethylene iodide, where the decomposition is followed using ultraviolet photoelectron spectroscopy. Carbenes hydrogenate o methane by reaction with surface hydrogen via a second-order reaction with an activation energy of 21 __ _ 2 kJ mol- 1. Experiments with deuterium show that there appears to be no hydrogen-deuterium exchange between the carbene and surface hydrogen. The carbene decomposition temperature increases with the addition of oxygen to the surface, and this effect is ascribed to the effect of site blocking rather than a chemical modification of the adsorbed carbene by coadsorhed oxygen. Similarly, although the methane desorption temperature increases with increasing oxygen coverage, this effect is found to be due to a change in the surface coverage of carbene and hydrogen rather than a chemical modification of the carbene itself. Finally, no ethylene or ethane are found to desorb from the surface. © 1997 Elsevier Science B.V. All rights reserved