Empty Orbitals of Adsorbates Determined by Inverse Ultraviolet Photoemission

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 2π* 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 EF. Chemisorbed oxygen has sharp 2px,y states at 1.4 eV above EF at k_∥=0 with the total density of states extending from EF to EF+2 eV in agreement with band calculations. This state disappears upon oxide formation.