DYNAMICAL PROPERTIES OF RH(111)H(1 X-1) SURFACE

In the experimental He atom scattering time-of-flight spectra of rhodi um covered with hydrogen there is no evidence of the anomalous high in tensity of the resonant mode present in the clean surface. In this pap er we explain the different behaviour of clean and covered rhodium (11 1) surface in terms of the ''corrugating'' effect of the electron dens ity of hydrogen atoms. For clean surface the surface electronic densit y is shifted with respect to the lattice atomic positions, i.e. there is an ''anticorrugating'' effect that enhances the intensity of the lo ngitudinal resonant mode which becomes dominant for some scattering ge ometries. For the covered surface the hydrogen atoms remove the antico rrugation, the charge profile becomes corrugated and the intensity of the longitudinal resonant vibrational mode remains very weak with resp ect to the Rayleigh wave intensity.