Core level spectroscopy of physisorbed molecules on graphite

Abstract

Several recent applications of high-resolution core-level spectroscopies to the investigation of physisorbed molecules (N 2 and O 2 on graphite) are reviewed. The ordered arrangements of the adsorbed molecules allow the distinction between σ and π molecular states revealing for instance a complex nature of the so called σ-resonance region. The molecular Rydberg states are found to persist in the adsorbates. An orientational phase transition of O 2 on graphite has been investigated using polarization dependent XAS. This phase transition also gives rise to pronounced changes in the XPS line profile due to a position dependent screening response from the substrate. The Auger spectrum of N 2 on graphite shows features corresponding to the decay of ionic as well as neutral states making it possible to determine the charge transfer rate for the neutralization process. The new possibility of recording autoionization spectra with vibrational selection in both the excitation and decay steps are demonstrated for adsorbed N 2.