Matrix elements in inverse X-ray photo-emission (bremsstrahlung isochromat spectroscopy)

Abstract
Transition matrix elements for photo-emission (X-ray photo-electron spectroscopy (XPS)) and inverse photo-emission (bremsstrahlung isochromat spectroscopy (BIS)) in the X-ray region are computed for 17 solid elements (Al, and the 3d and 4d series). The results show a strong dependence on atomic number, angular momentum quantum number and final-state energy. The origin of these effects is traced to the value of the final-state wavefunction in the core region of the atom for BIS (initial-state wavefunction for XPS). The results are discussed in terms of atomic number, band width and lattice constants. Finally, detailed comparisons are made with experimental BIS spectra of transition metals and transition-metal alloys, where it is shown that correct interpretation of spectra in terms of the density of states necessitates the inclusion of the matrix elements.