OBSERVATION OF THE REACTION OF GAS-PHASE ATOMIC-HYDROGEN WITH RU(001)-P(1X2)-O AT 100-K

The interaction of gas-phase atomic hydrogen with chemisorbed oxygen o n Ru(001) has been investigated with high-resolution electron energy l oss spectroscopy. As gas-phase hydrogen atoms impinge on the p(1X2) ox ygen overlayer at surface temperatures below 100 K, water is formed, a reaction which has not been observed in previous studies of coadsorbe d hydrogen and oxygen on Ru(001). The water molecules which are produc ed exist as adsorbed monomers initially but form clusters at greater e xtents of reaction. Since this reaction occurs at low surface temperat ures, an Eley-Rideal-like mechanism is suggested in which hydrogen ato ms from the gas phase react with adsorbed oxygen before being thermall y accommodated to the surface. More than 50% of the saturation coverag e of oxygen can be removed by means of gas-phase atomic hydrogen. Comp lete removal of the oxygen overlayer is inhibited by the water that is produced in the reaction.