Electron energy loss characterization of NO on Rh(111). II. Coadsorption with oxygen and CO

摘要

High resolution electron energy loss spectroscopy has been used to examine the effects of coadsorbed oxygen and carbon monoxide on the bonding of nitric oxide adsorbed on the Rh (111) surface. NO is converted from twofold bridge sites (1500ndash;1600 cmminus;1) to linear sites (1840 cmminus;1) when annealed to 275 K in the presence of coadsorbed oxygen. Terminally bound linear NO does not dissociate, but desorbs molecularly, a finding consistent with the commonly observed oxygen inhibition of NO dissociation over noble metals. Coadsorbed CO does not significantly inhibit or promote the dissociation of a low coverage of nitric oxide compared to the clean Rh (111) surface. CO and NO appear to segregate and form islands of each species at 95 K if CO is adsorbed first. Annealing this adlayer above 250 K disperses the islands and mixes the adsorbate layer at temperatures below where NO dissociation and reaction with CO are significant. The Rhndash;CO bond is weakened in wellhyphen;mixed CO+NO adlayers, indicating that the NOndash;CO repulsive interaction acts through the Rh substrate rather than directly between the adsorbed molecules.