ALKALI-METAL-AFFECTED ADSORPTION OF CO ON W(110) STUDIED BY METASTABLE IMPACT ELECTRON-SPECTROSCOPY

The adsorption of CO on clean and alkali-covered W(110) is studied by Metastable Impact Electron Spectroscopy (MIES) and UPS. Moleculary adsorbed CO is not observed for adsorption on clean W(110) neither by MIES nor by UPS at room temperature, but its existence cannot be excluded by the present results. From a comparison with data for the coadsorption of oxygen and K it is concluded that for K precoverages up to 0.8 ML features from the molecular adsorption of CO are seen in the MIE spectra. K precoverages beyond 0.8 ML, however, show spectral features corresponding to oxygen adsorption only. The exposure of a CO saturated W(110) surface to various amounts of K confirms that the complete disappearance of CO induced molecular spectral features occurs around 0.8 ML K coverage, and is mediated by a direct transfer of the K(4s) electron to the CO molecule.