RESONANT ELECTRON-SCATTERING OF PHYSISORBED O-2 ON AG(111)

Physisorbed O-2 on Ag(111) at mono- and multilayer coverages was studi ed by high-resolution electron energy-loss spectroscopy. As the excita tion mechanism, the (4) Sigma(u)(-) negative-ion resonance was chosen. The O-2 stretch mode and its overtones exhibit a strong rail to highe r loss energies. For the multilayer, a broad peak around 7 meV is obse rved. This observation and the lack of any larger intensity on the gai n side made it likely that vibrational energy quanta as large as 7 meV are the dominant contribution to the tail.