CO Chemisorption Effects on Cerium Initial and Final States in the Core Level Photoelectron Spectrum of CeIr2

摘要

Carbon monoxide (CO) adsorption on the mixed-valence compound CeIr2 has been studied by X-ray photoelectron spectroscopy. CO adsorption on this surface is predominantly molecular. We show that changes in the cerium 3d spectrum upon CO chemisorption may be separated into initial- and final-state effects. In the initial state, stabilization of the (Xe)(5d6s)34f1 configuration occurs due to an increase in effective nuclear charge on the cerium atom. This leads to a decrease in f0 intensity in the recorded spectrum. Increased f-electron repulsion in the final state raises the energy of the f2 final-state configuration and causes a 2.2-eV shift to higher binding energy of the 3d5/2f2 peak. The 0.5-eV binding energy shifts of the 3d5/2f1 and 3d3/2f1 peaks along with the 2.2-eV shift of the 3d5/2f2 peak indicate that the f orbitals are quite sensitive indicators of the surface oxidation state in this compound.