Oxygen-induced Rh 3d5/2 surface core-level shifts on Rh(111)

High-resolution measurements are reported of the surface core-level shift (SCLS) of the 3d level for the Rh(111) surface as a function of oxygen coverage Θ on the surface. These measurements are analyzed by density-functional theory calculations of the initial- and final-state contributions to the shifts. The calculations are found to reproduce well the trends and magnitudes of the experimental shifts. Adsorption of oxygen shifts the Rh 3d surface core levels to higher binding energies with the magnitude of the shift depending almost linearly on the coordination number of Rh surface atoms to O adatoms. The Rh 3d binding energy increases by about 0.3 eV per bond to an O adatom. This correlation is robust with respect to differences between initial- and transition-state theory calculations of the SCLS's. The results are discussed in a simple physical picture.