Surface vibrations of oxygen on W(100)

The localized surface vibrations of oxygen adsorbed on a clean W (100) surface were studied by high-resolution electron-energy-loss spectroscopy. At low coverages $\theta <0.25\mathrm{}$ a single surface vibration of the dissociated oxygen atoms is observed, while a rather complicated loss spectrum develops at higher coverages. Spectra of oxygen-covered annealed surfaces are also reported. Rather detailed models are presented for both surfaces, which are consistent with the number and frequency of the observed vibrations as well as with previous results on the same system. It is argued that the driving forces for the formation of the adsorbate superlattice are Coulomb repulsion and the energy gain in a surface disproportionation reaction.