Photoemission spectra of adsorbed layers on Pd surfaces

Abstract

Adsorption of CO, NO, H₂ and O₂ on (110) and polycrystalline Pd surfaces was studied by means of ultra-violet photoelectron spectroscopy (UPS) using Hel and Hell resonance radiation. Generally, a marked decrease of the emitted intensity from the energy range just below the Fermi level was observed after adsorption. Adsorption of CO causes the appearance of two peaks at 7.9 and 10.8 eV below E_f; after NO adsorption two maxima at 9.3 and 15.5 eV were observed. Absorption of oxygen leads to a peak at 5.8 eV. Attempts are made to correlate these additional structures with energy levels of the free molecules. The usefulness of the UPS technique in studying surface reactions is demonstrated with the thermal decomposition of NO as well as with the displacement of adsorbed NO by CO.