The surface vibrations of H adsorbed on W(100) at 300 K have been studied by electron-energy-loss spectroscopy. Two vibration modes corresponding to atomic hydrogen in two different sites have been found with the relative occupation depending on the total coverage. The single mode observed at high coverages is attributed to the occupation of bridge sites (${\beta }_1$ hydrogen) while the mode observed at low coverages is associated with on-top sites (${\beta }_2$ hydrogen).

• Received 19 January 1976

DOI:https://doi.org/10.1103/PhysRevLett.36.1549