A comparative study of CO and N2 adsorbed on clean and promoted transition metal surfaces by a combined use of EELS, XPES and UVPES

CO and N2 adsorbed on transition metal surfaces in the end-on (perpendicular)configuration and possessing bond orders not far below 3, show two-peak u.v. photoelectron spectra with little separation between the 1 π and 5σ levels. When the molecules are adsorbed on transition metal surfaces modified by Ba or At, the bond order of the adsorbate is close to unity in the case of CO and slightly less than two in the case of N2. These precursor states which undergo facile dissociation to atomic species show three.peak u.v. spectra with well-separated lπ and 5σ levels. The ordering of the In and 5a levels seems to be different in CO and N2 adsorbed on the promoted .surfaces; furthermore, the 4a level is shifted to higher energies in the former. UVPES results suggest that the orientation of the two molecules on the promoted surfaces are likely to be different.