Physical Principles of Electron Spectroscopy

Abstract

In the field of X-ray photoelectron spectroscopy there exists at present a large amount of experimental data that requires a complete theoretical analysis. Before the first papers reporting experimental data on photoelectron spectra were published, it was considered that the energy eigenvalues determined for multielectron systems by applying the Hartree-Fock or Hartree-Fock-Slater methods were an adequate approximation for the electron binding energies. However, it has been shown that the magnitude of the binding energies of deeply lying core electrons is affected significantly not only by relativistic effects but also by relaxation effects. Creation of holes in the photoionization process results in a modification of the electron wave functions of the system, and this introduces a significant contribution to the values of binding energies. However, in the case of core electrons, both the relativistic and the relaxation effects are not very sensitive to the environment of the given atom incorporated in a molecule or in a solid material, and consequently the magnitude of core-level chemical shifts is determined mainly by modifications of the density-of-state distribution of the valence electrons.