The electronic structure of the elements from gas-phase X-ray photoelectron spectroscopy

Abstract

Abstract This work deals with some recent developments in the study of atoms and molecules by X-ray photoelectron spectroscopy. The experimental techniques of high temperature measurement are discussed, followed by a treatment of core binding energies and the various contributions to their values, in particular relaxation, correlation and relativistic effects. Binding energies in both free atoms and free ions are discussed and compared with corresponding binding energies in molecules and solids. In addition to the ‘main’ peaks observed in photoelectron spectroscopy corresponding to ionization of electrons from various orbitals, weaker satellite structures are also observed, resulting from electron excitation accompanying core ionization. Comparison is made between the intensities of these satellites in various atomic core regions, as well as in molecules containing these atoms. Finally, the photoionization cross-section is shown to change dramatically with the change in the energy of the exciting photon; this appears to have diagnostic value in determining molecular orbital parentage. On the other hand, changes in the photoelectron intensity ratios of spin-orbit components with photon energy may be more subtle, but make possible a very rigorous test of theory.