Photoacoustic and Absorption Spectra of UF4

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Abstract
The visible and near IR spectrum of the U4+ ion has been studied by several authors, including aqueous solution studies1 and work on UF2,3 4, UC14 4, and U4+ in CaF2. The last experiment resulted in a spectrum which was sharper than that obtained for pure UF4, and the spectra features were assigned according to the prescription of Spedding.6 While good agreement between the calculated and experimental energies was obtained, the matter of U4+ site symmetry in CaF2 has not been resolved. The actual symmetry of U4+ in UF4 is an eight-cordinate, distorted square antiprism with U-F bond distances ranging from 2.249 Å to 2.318 Å (cf ref. 7, 8). Such low U4+ site symmetry makes a group theoretical analysis of electronic states from the f2 ion of little aid in the assignment of the Russel-Sanders atomic states and their respective J term microstates. This low site symmetry, and the resulting J term splitting, may in part cause the wide peak widths observed in UF4 (and U02).