Inner electron binding energy in atoms and ions

The Is-electron binding energies of first and second row atoms were obtained from Clementi's analytical Hartree-Fock wavefunctions with the use of Koopmans' theorem. These were compared with the differences of the expectation values of r(-1) between various low lying states of the charged and neutral atoms. and the ground state of the neutral atom. Good agreement was found. Extension of this analysis to molecules and crystals should make possible a better interpretation of the chemical shift observed in photoelectron spectroscopy.