CALCULATED ION-ATOM CORE-LEVEL SHIFTS FOR USE IN ESTIMATING ATOMIC AND IONIC RADII OF FREE ATOMS AND IONS

In X-ray photoelectron spectroscopy (XPS) core-level shifts of an atom in different chemi-cal environments, including the atom-free ion chemical change, result from both initial- and final-state effects (Egelhoff, 1987). The initial state effect is a static shift in the orbital energies in the ground state of the atom before core ionization. It is directly related to the nature of the chemical bonds in which the atom is involved. The charge distribution of an atom in molecules or solids, or as a free ion, in fact, changes the potentials of core electrons, even though the spa-tial character of the core electron wave function remains strongly localized within the atom. Instead, the final state effects are related to the degree to which core and valence electrons and the environment of the atom can polarize in response to ionization.