HREELS investigation of physisorbed molecules on single- crystalline surfaces through dipole and resonant electron-scattering mechanism

Abstract

Monolayer (ML) and multilayer of CO and N 2, physisorbed on Al(111), Ag(111), and Pd(111) surfaces at about 20 K have been investigated by high-resolution electron energy-loss Spectroscopy (HREELS) and UV photoelectron Spectroscopy (UPS). In the physisorption state, electron scattering via a negative-ion resonance (NIR) is the dominant process for N 2 at all coverages and for CO above the ML. Fingerprints of NIR scattering are a resonance in the primary energy of the excitation probability, the peculiar angular distribution of the scattered electrons, and the high overtone intensity of the intra- and inter-molecular vibrations. The lifetime of the NIR is discussed and examples for complete quenching of the NIR in physisorbed N 2 and CO are presented.