Determination of effective atomic charge,extra-atomic relaxation and madelung energy in chemical compounds on the basis of X-ray photoelectron and auger transition energies

Abstract

A new method is proposed for the determination of effective atomic charge, extra-atomic relaxation, and Madelung energy in chemical compounds, based on the experimentally measured energies of X-ray photoelectron and Auger transitions. The method has been applied to solid compounds of the elements from Na to Cl, and to a number of free sulfur-, phosphorus-, silicon-, and chlorine-containing molecules. The experimental energies are represented as consisting of two parts. The first part is determined by the ionization energy of a free ion with a given effective charge, and includes the intra-atomic relaxation. The second part is determined by the Madelung energy and the extra-atomic relaxation. The first contribution is calculated by using the Hartree-Fock method. The effective atomic charges required have been found from the shifts of Kα-lines in the X-ray spectra. The extra-atomic relaxations are obtained as the differences between experimental and theoretical Auger parameters, and the values calculated are the additive functions of ligands of the atom studied. The increments of the additive scheme correlate with the ligand refractions. The effective charges, extra-atomic relaxation energies and Madelung potentials obtained from ESCA and AES data agree well with both calculated and direct experimental results.