Physisorption and Chemisorption Effects on Atom—Adsorbate van der Waals Potentials. Application to He and He* Scattering from Adsorbed CO

Abstract

AbstractThe dynamical polarizability of an atomic or molecular species may undergo significant changes upon physical and chemical adsorption onto a metallic substrate. The physical effect derives from the presence of the polarizable substrate surface which gives rise to a modification of all the polarization induced or van der Waals potentials acting between the adsorbate and the nearby atoms or molecules in the gas phase. The chemical effect, viz. chemisorption, may give rise to the broadening of adsorbate valence orbitals into resonances which will be occupied up to the substrate Fermi level. Provided the electronic density of the localized resonance states at the Fermi level is non‐vanishing, chemisorption will open a new channel of intra‐adsorbate dynamic polarizability. Both effects (i.e. the physical and the chemical one) will enhance the total van der Waals potentials encountered in the thermal energy atom scattering and Penning spectroscopy of adsorbates. Calculations are made of these effects on the adsorbate—gas phase atom van der Waals potentials and their influence on the thermal energy atom scattering (TEAS) cross sections and the effective Penning deexcitation energies discussed for the case of He and He* collisions with adsorbed CO.