Resonant electron scattering of physisorbed O2 on Ag(111)

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