Anharmonic contribution to the temperature dependence of photoemission core-level spectroscopy of adsorbates on surfaces: Oxygen on Rh(110)

High-resolution x-ray photoelectron spectroscopy has been used to investigate the temperature behavior of the O $1s$ and O $2s$ core-level photoemission signals from the $\mathrm{O}-(2\mathrm{}\times 2)p2mg$ structure on Rh(110). With increasing temperature we observe a continuous shift of the photoemission peaks to lower binding energy. The width of the peaks increases with increasing temperature, as previously reported for other systems. Since the adsorption site of the O atoms is independent of temperature, the phenomenon is interpreted as due to anharmonic contributions to the potential-energy curve.