Auger parameter shifts in the case of the non-local screening mechanism: Applications of the electrostatic model to molecules, solids and adsorbed species

A simple electrostatic model is applied to predict and rationalize the Auger parameter shifts in molecules, solids and adsorbed species. The model is valid in the case of the non-local screening mechanism, i.e. when the screening of the core hole is due to the polarization of the nearest-neighbour ligands (no charge transfer from the ligands to localized electronic levels of the atom with the core hole, as occurs with the main peak of the core-ionized heavier 3dn transition metal ions or the light lanthanide ions). To good approximation it is shown that: (1) the Auger parameter shift is a function of the number, distance, electronic polarizability and local symmetry of the first-neighbour ligands of the core-ionized atom; (2) the dipole-dipole interactions can play a key role in determining the extent of the extra-atomic relaxation energy and hence of the Auger parameter shift.