THE EXTRA-ATOMIC RELAXATION AND ENERGY RELATIONS ON THE ADSORBATE-SUBSTRATE INTERFACE

Energy relations important for the photoionization processes on the adsorbate-substrate interface are obtained with the help of smooth matching between the image potential outside the substrate and the exchange-correlation potential in the substrate bulk. Using these relations the extra-atomic relaxation for the electron levels of physisorbed atoms and molecules can be represented in a simple analytical form. It is then possible to obtain a general equation C - Delta phi = E(b)(F) + phi, where E(b)(F) is the binding energy with respect to the Fermi level, phi is the work function of the clean substrate and Delta phi is the change of the work function after adsorption, The calculated C values for Xe5p, Xe3d, and sigma(g), pi(u) and sigma(u) levels of N-2 molecules equal 11.6 eV, 65.7 eV, 13.6 eV, 15.0 eV and 16.8 eV, respectively, and are in good agreement with the experimental data. A similar relation is also obtained for the physisorption on the surface steps. The PAX method is discussed in connection with these relations. The presence of the induced Friedel oscillation in the final photoionization state is shown with the help of the experimental extra-atomic relaxation values. These oscillations are important for the difference in extra-atomic relaxation energy for valence and inner levels of the same atom or molecule and connect the extra-atomic relaxations of the valence levels with the spatial distribution of the corresponding wave functions.