RAIRS Characterization of CO and O Coadsorption on Cu(111)

In a study preliminary to investigating CO₂ dissociation, we report our results on oxygen and carbon monoxide coadsorption on Cu(111). We use reflection adsorption infrared spectroscopy and Auger electron spectroscopy to characterize and quantify adsorbed species. On clean Cu(111), the CO internal stretch mode appears initially at 2077 cm^-1 for a surface temperature of ∼80 K. We accurately reproduce the previously determined redshift of the absorption band with increasing CO coverage. We subsequently oxidize the surface by exposure to O₂ at 300 K to ensure O₂ dissociation. The band's frequency and line shape of subsequently adsorbed CO at ∼80 K are not affected. However, the maximum absorbance and integrated peak intensities drop with increasing O coverage. The data suggest that CO is not adsorbed near O, likely as a consequence of the mechanism of Cu(111) surface oxidation by O₂ at 300 K. We discuss whether our RAIRS results may be used to quantify CO₂ dissociation in the zero-coverage limit.