Frank deGroot: Transition metal K edge spectral shapes: The influence of core hole screening

Using High-Energy-Resolution-Fluorescence-Detection (HERFD), one can sharpen the pre-edge structures revealing their multiplet nature. In ionic systems, they can be calculated from the transition from the 3dN ground state to the 1s13dN+1 final state, where covalent systems need the inclusion of charge transfer effects.[1] The main edge is usually interpreted from the calculation of the transitions to empty states, using DFT theory, for example multiple scattering (FEFF). The 1s XPS spectra of transition metal oxides show multiple peaks, implying that one photon energy gives rise to electrons with multiple kinetic energies. This implies that the 1s XAS spectral shape must be described as the convolution of the empty states with the 1s XPS spectral shape [2]. Isolated transition metal ions only show a pre-edge and an edge, but bulk oxides show additional intensity between the pre-edge and edge. One can show that this intensity is related to dipole transitions of metal p-character that is part of the 3d-states of a near-neighbour metal ion [3]. X-MCD measurements of CrO2 reveal that the pre-edge is invisible in normal XAS [4]. In systems with two different metal ions one can observe the metal-metal charge transfer in the non-local peaks. [5]

References:
[1] J. Phys. Cond. Matt. 21, 104207 (2009).
[2] Ghiasi et al., Phys. Rev. B. 100, 075146 (2019).
[3] Juhin et al., Phys. Rev. B. 81, 115115 (2010).
[4] Zimmermann et al., J. Elec. Spec. 222, 74 (2018).
[5] Juhin et al. Inorg. Chem. 56, 10882 (2017).