An analysis was made of the energy levels of U6+O5F and U5+O5F centers with C4v symmetry. The experimental energies of the fine-structure lines of seven p-f transitions of the prominent (U6+O5F)5+ center with C4v symmetry were deduced from well-resolved absorption spectra in the ultra-violet range and from polarized emission and excitation experiments at 18000 to 40000/cm. A comparison with the f-f energy levels of U5+, previously observed in X- or γ-irradiated UO5F centers, showed that the energies of the p-f transitions of U6+ could be approximately accounted for by shifting the energies of the f-f transitions of U5+ by 19493/cm. The shift represented the energy difference between the center of gravity of the fine-structure levels of the first excited level, and the fundamental level of the configuration 5f0. An analysis of the fine-structure lines associated with the p-f transitions, and a comparison with the relativistic electronic structures of the 5f0 and 5f1 configurations of cubic molecules, UF6, UF8- and NpF6, were performed in order to determine which p and f orbitals were associated with the observed p-f transitions of U6+.

p-f and f-f Transitions of U6+O5F and U5+O5F Centers in LiF. R.Parrot, D.Boulanger, F.Gendron, C.Naud: Physical Review B, 2004, 69[3], 035112 (6pp)