Coadsorption of H and CO on Gd(0001)

We report on the electronic structure of hydrogen and carbon monoxide on Gd (0001) and the development of the adsorption processes studied by means of photoelectron spectroscopy in combination with scanning tunneling microscop y. The adsorption process of a hydrogen covered Gd film being exposed to ca rbon monoxide consists of five steps. At the beginning the whole amount of adsorbed hydrogen atoms is removed from the surface. In the intermediate re gime, carbon and oxygen is adsorbed at or near the surface. The last step d emonstrates the oxidation to Gd2O3 acting as a catalyst for the transformat ion of CO to CO2 which creates stable carbonate species at the surface. Thi s formation occurs also for the adsorption of oxygen and carbon monoxide. T he visualization of the adsorption process during specific steps is obtaine d by STM. (C) 1999 Elsevier Science B.V. All rights reserved.