Origin of the chemical shift in X‐ray absorption near‐edge spectroscopy at the Mn K ‐edge in manganese oxide compounds

The absorption edge in Mn K ‐edge X‐ray absorption spectra of manganese oxide compounds shows a shift of several electronvolts in going from MnO through LaMnO 3 to CaMnO 3 . On the other hand, in X‐ray photoelectron spectra much smaller shifts are observed. To identify the mechanisms that cause the observed chemical shifts, 1 s ionization as well as 1 s → “4 p ” transition energies have been determined by electronic structure calculations on embedded Mn ions and embedded MnO 6 clusters. Systematic variation of the cluster geometry and the cluster embedding showed that the chemical shifts are predominantly determined by two effects: the changes in the Mn 3 d occupation and the changes in the Madelung potential. The large chemical shift in the 1 s → 4 p transition energies between different materials occurs because the two effects do not compensate each other. The chemical shifts obtained for the embedded MnO 6 clusters agree reasonably with the experimental shifts. The small sensitivity to the material observed for the Mn 1 s ionization energies is explained by the near cancellation of the effects of the Madelung potential and the 3 d occupation of the Mn ion. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2003