Crystal-field splitting strength of U-6d orbitals in NaUO₃, KUO₃ and RbUO₃

Here, the uranium valence electronic structures in the perovskite-based ternary uranate systems NaUO₃, KUO₃ and RbUO₃ are reported on the basis of high-energy resolved fluorescence-detected X-ray absorption spectroscopy experiments at the U L₃ edge and relativistic quantum chemistry calculations based on density functional theory. Advanced theoretical simulations allowed us to identify the origin of spectral features and to assess the impact of structural distortion within the oxygen octahedra. The octahedral crystal-field strength extracted from both experiments and calculations is reported for all three compounds.