Chemical bonding effects in the inverse photoemission spectra of chemisorbed CO

The inverse photoemission spectra of CO chemisorbed on several transition metal surfaces shows a broad, = 3 eV full-width at half-maximum, resonance associated with the CO 2π* level. For CO/Cu(100), there is a doublet rather than a single broad peak. We interpret the chemisorbed CO structure as being due to chemical bonding effects in the anionic system. An electron may be added into one of two distinct kinds of orbitals. In the first kind, associated with lower energy ionic states, the orbital is bonding between CO(2π*) and the surface conduction band; in the second kind, the orbital is anti-bonding. This interpretation is based on ab initio Hartree-Fock wavefunctions for CunCO clusters. © 1985.