Observation of Nondipole Electron Impact Vibrational Excitations: H on W (100)

High-resolution inelastic electron spectra have been measured for a saturated coverage of atomic hydrogen adsorbed on W(100). The fundamental modes corresponding to H occupying a $C_{2v}$ point-group-symmetry bridge site plus an overtone ($v=0\mathrm{}\to 2$) of the intense symmetric stretch are resolved at angles off the specular direction. The intensity of these modes (normalized to the elastic peak) exhibits resonantlike behavior as a function of the impact energy.