Empty Orbitals of Adsorbates Determined by Inverse Ultraviolet Photoemission

Abstract

The position of the lowest empty orbitals of CO and O chemisorbed on Ni(111) have been determined by use of inverse photoemission in the ultraviolet. The $2{\pi }^{*}$ orbital of CO is lowered by 4.5 eV upon chemisorption and broadened to a 5.5-eV-wide resonance centered 3.5 eV above $E_{\mathrm{F}}$. Chemisorbed oxygen has sharp $2p_{x,y}$ states at 1.4 eV above $E_{\mathrm{F}}$ at $k_{\parallel }=0\mathrm{}$ with the total density of states extending from $E_{\mathrm{F}}$ to $E_{\mathrm{F}}+2\mathrm{}$ eV in agreement with band calculations. This state disappears upon oxide formation.