CORE-LEVEL SPECTROSCOPY OF PHYSISORBED MOLECULES ON GRAPHITE

Several recent applications of high-resolution core-level spectroscopi es to the investigation of physisorbed molecules (N2 and O2 on graphit e) are reviewed. The ordered arrangements of the adsorbed molecules al low the distinction between sigma and pi molecular states revealing fo r instance a complex nature of the so called sigma-resonance region. T he molecular Rydberg states are found to persist in the adsorbates. An orientational phase transition of O2 on graphite has been investigate d using polarization dependent XAS. This phase transition also gives r ise to pronounced changes in the XPS line profile due to a position de pendent screening response from the substrate. The Auger spectrum of N 2 on graphite shows features corresponding to the decay of ionic as we ll as neutral states making it possible to determine the charge transf er rate for the neutralization process. The new possibility of recordi ng autoionization spectra with vibrational selection in both the excit ation and decay steps are demonstrated for adsorbed N2.