The interaction of hydrogen with the Rh(1 1 1) surface was studied by means of high-resolution real-time X-ray core-level photoemission. The analysis of the intensity of the Rh3d(5/2) core-level components was used to determine the hydrogen adsorption sites as a function of the hydrogen dose. While at low coverage only three-fold adsorption sites are occupied, at higher hydrogen concentrations bridge species are also present. The temperature dependence of the core-level spectra indicates that during desorption, surface depopulation occurs in an almost reverse order with respect to the adsorption process.
