A RAIRS study of methoxy and ethoxy on oxidised Cu(100)

The adsorption and reaction of methanol and ethanol on a preoxidised Cu(100) surface was studied with Reflection-Absorption Infra-Red Spectroscopy (RAIRS). Both alcohols reacted with the modified surface well below room temperature, undergoing OH bond scission to form alkoxide species. The alkoxides were stable up to 340-360 K at which stage they desorbed as aldehydes. Vibrational assignments of the observed modes were made with reference to the RAIRS spectra of the alcohols and their deuterium substituted analogues on Cu(100) together with literature values for the gaseous, liquid and solid alcohols. Application of the metal surface selection rule to the alkoxide spectra indicate that in both cases the C-O bond lies perpendicular to the surface. The methoxy species is therefore assigned to an upright C-3v configuration. Oxygen precoverage is found to govern the amount of alkoxide formation which passes through a maximum at a precoverage of about 150 L.