Final-state screening and chemical shifts in photoelectron spectroscopy

Photoelectron spectroscopic measurements of core-electron levels in cations of transition-series insulators commonly show ``satellite'' features in the vicinity of the ``main'' photoelectron peaks. In this paper, the relationship between main lines and adjacent satellites is systematically examined for 3d-series insulators. The spectral features are interpreted using a relaxation model that allows for the possibility of different final-state screening conditions of the photoinduced hole. Systematic trends are examined by employing atomic calculations and utilizing transition-state theory to calculate electron removal energies for atoms in appropriately simulated chemical environments. It is demonstrated that the main-line and satellite energies are both dependent on the cation charge environment but with different degrees of sensitivity. The consequence is that sensitivity to chemical change can be monitored in the observed main-line to satellite separation. Model predictions are tested by monitoring the dependence of the satellite separations on the cation valence state and on the electronegativity of both cations and ligated anions. Systematic tests are applied to 3d-series insulators but more general applicability of the relaxation model is also discussed.