Temporary Negative-Ion Formation in Chemisorbed Species: The Energy and Angular Dependence of Vibrational Losses for Electron Scattering Studies of HCOO/Ni(110)

We have studied both the energy and angular dependence of vibrational losses for the formate species chemisorbed on Ni(110), using high-resolution electron-energy-loss spectroscopy. Temporary negativeion formation, at an incident electron energy of {~} 14 eV, leads to a dramatic enhancement in the intensity of the symmetric O-C-O stretch. Electron emission shows a strong angular dependence which peaks at high emission angles away from the surface normal. This effect is compared to previous photoemission studies of adsorbed CO, where the scattering in the σ-shape resonance is directed along the C-O bond.