Relaxation shifts, line shapes and satellites in the x-ray and absorption spectroscopy of adsorbed species

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Abstract
Calculations of relaxation shifts, X-ray edge line shapes and satellites appearing in the photoemission and absorption spectra of adsorbate electron levels are presented. The formalism of the surface response function is developed for treating the nonbonding surface induced effects in adsorbate electron states. It is shown that relaxation shifts and asymmetric level broadening characteristic of adsorbate core level X-ray photoemission spectra can be ascribed to screening and shake up processes in metallic substrates. The role of the dynamic screening in production of inelastic satellite structure in XPS of core levels is examined and the variation of the satellite intensity and spread with the adatom separation from the surface is calculated. Level shifts and satellites appearing in absorption spectroscopy of core → valence level electron transitions in adsorbed atoms are discussed within a simple model of a chemisorption system which accounts for both chemical bonding and screening effects. A complete solution to the problem is obtained in the weak coupling limit using a special perturbation expansion. The results for the magnitude of relaxation shifts and satellite intensity differ remarkably from the corresponding ones in XPS