Vibrationally and Orientationally Selective Probing of Intramolecular Potentials in Physisorbed Molecules

In the ${\mathrm{N}}_2$/Xe/Pt(111) physisorption system, differences between ${\mathrm{N}}_2$ valence orbitals parallel and perpendicular to the surface are demonstrated by polarization-dependent vibrationally resolved autoionization spectroscopy and calculations using a self-consistent image charge model. The adsorbate-substrate interaction is shown to affect the intramolecular bonding. The results disagree with the "hole hopping" model recently introduced in order to explain the differences in the valence photoemission vibrational progressions between free and physisorbed molecules.