SURFACE PHONONS OF HYDROGEN ON TUNGSTEN

The surface photons of a monolayer of hydrogen atoms chemisorbed on W(001) surface have been studied within the two-dimensional Brillouin zone. A lattice-dynamical model incorporating central forces up to third neighbors and the angular forces up to first neighbors between the adsorbate and substrate is employed. The adatom-adatom central interactions have also been included. The comparison with the experimental data enables us to obtain the magnitude of some of the force constants. Calculations have also been performed for Debe and Kings's model {11} for W(001) c{2 × 2}H reconstructed substrate surface. If we assume a W-H bond length just equal to that seen in the unreconstructed surface, we find it necessary to assume large displacements of W atoms (d > 0.5 A ̊) in order to understand the viriation of photon frequencies with coverage recently observed in electron energy loss spectroscopy within the framework of a Debe and King model considering W-H central interactions up to third neighbors. © 1979.