Surface phonons on the Pt(111) surface: a comparison of He-scattering experiments with lattice dynamical calculations

Angular distributions and surface-phonon dispersion curves have been measured by He-atom scattering for clean Pt between T=160 and 373 K and for Pt-H(1 71) at 160 K along the \u3008110\u3009 and \u3008112\u3009 azimuths. Inelastic-scattering intensities over a wide range of wave vectors are also reported for the clean surface. The results are analyzed with use of the distorted-wave Born approximation for a model potential describing the He-atom\u2013Pt-surface potential. A set of 14 force constants adjusted to the bulk-phonon dispersion data cannot explain the measured time-of-flight spectra and the observed first-layer relaxation. However, by modifying at the surface the nearest-neighbor tangential force constants (\u3b11\u2019\u2019=1.7\u3b11b, and \u3b11\u2019=1.3\u3b11b), the radial force constants (\u3b21\u2019\u2019=0.39\u3b21b), and the three-body force constant (\u3b31\u2019\u2019=0.037\u3b31b)\u2014 where the superscripts 25 and a5 denote forces within the surface plane and between the first and second planes, respectively\u2014a good fit to all the data is achieved. The new surface force constants are discussed in terms of electronic-charge redistribution within the first layer