The insufficiency of the charge transfer model for resonant XES in UF₄

Recently, it was suggested that the single-electron charge transfer model (ligand 2p to Uranium 5f transition) could be used to explain the U M_4,5 Resonant X-ray Emission Spectroscopy (XES) of uranium dioxide (UO₂) and uranium tetrafluoride (UF₄) (Tobin et al. (2022) J. Phys. Cond. Matter 34:505601). Here, it is shown that this model produces results inconsistent with a joint consideration of both of the bandgaps of UO₂ and UF₄ and is thus insufficient to explain the observed behavior. An alternative Raman-based model is proposed.