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 microscopy. The adsorption process of a hydrogen covered Gd film being exposed to carbon monoxide consists of five steps. At the beginning the whole amount of adsorbed hydrogen atoms is removed from the surface. In the intermediate regime, carbon and oxygen is adsorbed at or near the surface. The last step demonstrates the oxidation to Gd2O3 acting as a catalyst for the transformation of CO to CO2 which creates stable carbonate species at the surface. This formation occurs also for the adsorption of oxygen and carbon monoxide. The visualization of the adsorption process during specific steps is obtained by STM. q1999 Elsevier Science B.V. All rights reserved