Interpretation of absorption edges by resonant electronic spectroscopy: experiment and theory

Resonant electronic spectroscopy consists in measuring a non-radiative decay process (Auger or autoionization process) excited with photon energies around an absorption edge. The resonant spectra carry information both on the nature of the electronic transitions near the absorption edge by scanning the very first empty orbitals above the Fermi level (through the absorption process), and, on the other hand, on the atomic electronic configuration through the lineshape of the observed decay process. In this paper, after a quick review of the pioneering works in this field, we show that resonant measurements and their theoretical modeling can be used to precisely interpret complex absorption spectra. Hence, Ce resonant 3d photoemission spectra allow, in the Ce-L3 edge, to attribute the two white lines to 4f1 and 4f0 final state electronic configurations and to evidence the presence of a hidden 4f2 structure in the rise of the absorption threshold. Quadrupolar transitions towards localized 3d orbitals are also detected and quantitatively characterized in the titanium K-edge prepeaks in TiO2, thanks to angular dependent resonant Ti-KLL Auger measurements