Application of multi‐edge HERFD‐XAS to assess the uranium valence electronic structure in potassium uranate (KUO3)

The uranium valence electronic structure in the prototypical undistorted perovskite KUO3 is reported on the basis of a comprehensive experimental study using multi‐edge HERFD‐XAS and relativistic quantum chemistry calculations based on density functional theory. Very good agreement is obtained between theory and experiments, including the confirmation of previously reported Laporte forbidden f–f transitions and X‐ray photoelectron spectroscopic measurements. Many spectral features are clearly identified in the probed U‐f, U‐p and U‐d states and the contribution of the O‐p states in those features could be assessed. The octahedral crystal field strength, 10Dq, was found to be 6.6 (1.5) eV and 6.9 (4) eV from experiment and calculations, respectively. Calculated electron binding energies down to U‐4f states are also reported. By combining HERFD‐XAS at the uranium L1‐, L3‐ and M4‐edge with relativistic quantum chemistry calculations the uranium valence electronic structure in KUO3 could be assessed in detail. The contribution of uranium and oxygen states in observed spectral features is discussed.