Electronic structure of solid uranium tetrafluorideUF4

Abstract

X-ray photoelectron spectra (XPS) and conversion electron spectra of the outer $(0--15\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ and inner $(15--40\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ valence electrons for ${\mathrm{UF}}_{4}$ were measured. Relativistic ${X}_{\ensuremath{\alpha}}$ discrete variation ($R{X}_{\ensuremath{\alpha}}$ DV) calculation data for the ${\mathrm{UF}}_{8}^{4\ensuremath{-}}\phantom{\rule{0.3em}{0ex}}({\mathrm{C}}_{4v})$ cluster reflecting uranium close environment in solid ${\mathrm{UF}}_{4}$ were used for the quantitative interpretation of the fine spectral structure. Quantitative agreement between the experimental and theoretical data was established. The $\mathrm{U}\phantom{\rule{0.3em}{0ex}}5f$ electrons ($\ensuremath{\approx}1$ $\mathrm{U}\phantom{\rule{0.3em}{0ex}}5f$ electron) were shown to participate directly in the chemical bond formation. This U 5$f$ electron was shown to be delocalized within the outer valence molecular orbitals (OVMO) range $(1--15\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$. The other $\mathrm{U}\phantom{\rule{0.3em}{0ex}}5f$ electrons were shown to be localized and to participate weakly in the chemical bond formation. The XPS line associated with these electrons was observed at $3.8\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The vacant $\mathrm{U}\phantom{\rule{0.3em}{0ex}}5f$ states are generally delocalized in the range of the low positive energies (0--7 eV). The contribution of the $\mathrm{U}\phantom{\rule{0.3em}{0ex}}6p$ electronic density to the molecular orbitals of ${\mathrm{UF}}_{4}$ was experimentally and theoretically evaluated. The $\mathrm{U}\phantom{\rule{0.3em}{0ex}}6p$ electrons were experimentally shown to participate significantly ($0.6\phantom{\rule{0.3em}{0ex}}\mathrm{U}\phantom{\rule{0.3em}{0ex}}6p$ electrons) in the formation of the OVMO beside the formation of the inner valence molecular orbitals (IVMO). IVMO composition and sequence order in the binding energy range $15--40\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ in ${\mathrm{UF}}_{4}$ were determined.