Electronic and vibronic states of uranium hexafluoride in the gas and in the solid phase at very low temperatures

Abstract

Complex vibronic structure has been observed in the electric-dipole-forbidden charge transfer absorption bands of solid and matrix-isolated UF 6 in the temperature range 8-14 K. These bands have their maximum intensity near 260 and 375 nm. Associated with the 260 nm band are four electronic transitions with origins at 30331, 31032, 32120, and 32821 cm-" the first two being observed directly. Two more nophonon transitions are associated with the weak band at 375 nm, one at 24564 cm-I and another at 25265 cm-I . These levels are assigned via a weak j-j coupling scheme as excitations from the ligand tluG" orbital to empty uranium Sf orbitals. Uranium spin-orbit coupling in UF 6 charge transfer states strongly resembles that of UF 6 -. Several progressions in the symmetric stretch frequency VI = 580-595 cm-I are present which have as their origins various combinations of the above electronic levels with the bending modes V" vs, and V6 or their overtones 2v •• 2vs, and 2V6' Temperature effects, which account for the principal differences between the gas and solid spectra, are also discussed. A much more intense band at 214 nm is lacking in vibronic structure and is attributed to an allowed charge transfer transition.Although the Cary 14 spectrometer appeared to have more than adequate resolution for the UF 8 spectrum, a

Theoretical Investigations of Geometry, Electronic Structure and Stability of UO6: Octahedral Uranium Hexoxide and Its Isomers†

“…U 6+ (F − ) 6 is a closed-shell species with a HOMO−LUMO Kohn−Sham energy-gap around 2.6 eV (the experimental gap from electronic excitation is 3.1 eV) . The 4t 1u (g 3/2u ) HOMO is dominantly F-2p, and the 1a 2u (e 5/2u ) LUMO is dominantly U-5f.…”

The electronic spectra of alkali metal uranates and band assignments: an analysis of their diffuse reflectance spectra

“…An analysis of the charge transfer transitions within the octahedral uranate group, has been performed on the UO 6 6~, basis of the calculations of the electronic structure of uranium hexaÑuoride, which is isoelectronic with and UF 6 , U O 6 6h as been studied in detail.4,25h27 In total, from 18 to 20 charge transfer transitions have been theoretically predicted in the electronic spectrum of above 24 400 cm~1 (below 410 UF 6 nm),25,26 but only six were experimentally observed. 25 Lewis et al 26 proposed that 5f-, 6p-, 6d-and 7s-uranium orbitals are employed in the formation of molecular UF 6 orbitals. The same approach was subsequently adopted upon analysis of transitions in uranate compounds based on regular octahedral site symmetry.…”

Photoelectron spectroscopy and theoretical studies of UF5− and UF6−

“…8 All six fundamental modes of vibration for the highly symmetric O h UF 6 are known from Raman and infrared spectroscopy. [9][10][11][12][13][14][15][16] The electronic structure of UF 6 has also been well studied with absorption spectroscopy, [17][18][19] electron impact spectroscopy, 20,21 and photoelectron spectroscopy (PES). 22,23 To understand these available experimental data, computational actinide chemistry has experienced a steady growth in developing better relativistic quantum chemistry methods.…”