Helium atom scattering study of the frustrated translation mode of CO adsorbed on the Cu(001) surface

摘要: The structure and vibrational modes of CO adsorbed on Cu(001) have been investigated by helium atom scattering (HAS). Below coverages θ=0.13, adsorbs as isolated molecules, the time flight (TOF) spectra atoms scattered from surface are characterized energy losses gains 3.94 ± 0.07 meV. With aid isotope shift measurements, this mode is unambiguously assigned to frustrated translation CO. In c(2×2) (θ=0.5) found show dispersion in both 〈100〉 〈110〉 azimuths with frequencies ranging 3.9 meV at zone origin 5.6 boundary. A simple force constant model a single nearest neighbor within layer be sufficient describe dispersion. For slightly less than θ=0.5 angular distributions features characteristic vacancies overlayer. TOF an additional nondispersive about 4 also seen molecules adjacent Rayleigh clearly observed but decrease frequency while longitudinal resonance, which especially prominent clean surface, disappears completely. results interpreted slab calculations.