HREELS INVESTIGATION OF THE COADSORPTION OF CO AND NO ON NI(111) AT ROOM-TEMPERATURE

The adsorption of CO and NO, and the coadsorption of both species on N i(111) at room temperature, has been studied by high resolution electr on energy loss spectroscopy. Both CO and NO molecules adsorb whithout dissociation, giving the well-known c(4x2) LEED pattern. In the case o f coadsorption, preadsorbed CO molecules are easily removed by incomin g NO, whatever the initial CO coverage. In the reverse case, preadsorb ed NO molecules inhibit CO adsorption for initial NO coverages higher than about 0.1 ML. For lower NO coverages, CO are allowed to adsorb, b ut their vibrational spectrum is substantially different from that obs erved for CO adsorption on the clean surface. The results are interpre ted in terms of the different electronic structure of the two molecule s.