Electronic spectroscopy of UF6 and WF6 by electron impact

Abstract

The electron-impact excitation spectra of uranium hexafluoride (UF6) and tungsten hexafluoride (WF6) have been studied experimentally at impact energies of 30, 50, and 75 eV and at scattering angles from 5° to 80°. Eleven features in UF6 are observed with maxima at 3.26, 4.2, ∼4.7, 5.8, 7.0, 7.86, 9.26, 11.01, 11.75, 12.5, and 13.2 eV. Four features in WF6 are observed with maximum intensity at 7.25, 7.9, 8.5, and 9.85, in good agreement with optical work. In addition, three previously unobserved features in WF6 at 11.75, 12.6, and 13.5 eV are reported. Similarity between the spectra of UF6 and WF6 suggests that the primary contribution to the absorption intensity in UF6 above 5.8 eV and in WF6 results from charge transfer transitions from fluorine p orbitals to metal d orbitals. Tentative assignments based in part on recent theoretical studies are made.

Theoretical studies on the physical properties and bonding of the 5d metal hexafluorides using the multiple scattering X.alpha. technique

“…The transition observed at 11.75 eV could not be fitted by eq 2 and is therefore assigned as a Rydberg transition in agreement with the assignment given in ref 40. However, our other assignments differ considerably from those qualitatively suggested in ref 40, in which a one-to-one correspondence between the spectra of WFe and UFe was assumed. Our Xa calculations of UFe28 and WFe do not show such a one-to-one correspondence in the order of either the one-electron energies or the calculated IPs.…”

“…In the case of uranium hexafluoride the main bonding is between the metal 5f orbitals and ligand SALCs of a2u, t2u, and t;u symmetry. The interaction between these SALCs and the 5f orbitals stabilizes orbitals of this symmetry which results in a different order in the energy levels of UF6 than in WFe so that there is not a one-to-one correspondance between the IPs of the two molecules as assumed by Rianda et al 40 Nonrelativistic MSXa14•28 calculations predict that electron attachment to UF6 takes place into an a2U orbital which is almost entirely f electron in character. Very recent OSMSXa calculations by Boring and Wood,44 who included relativistic corrections within the multiple scattering formalism, predict that the EA of UFg is decreased by about 1 eV compared to the nonrelativistic result.14…”

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.…”

Electron scattering from hexafluoride molecules: WF6and C2F6. Absolute total cross section measurements from 1 to 250 eV

“…Studies of electron scattering on a tungsten hexafluoride (WF 6 ) molecule have so far been rather incidental and have been mainly focused on the formation of negative ions (Thynne and Harland 1973, de Wall and Neuert 1977, Hildenbrand 1977. Rianda et al (1979) have studied the electron-impact excitation spectra in a crossed-beam experiment. Formation of WF − 6 and its dissociative products in electron transfer reactions was investigated by Dispert and Lackmann (1977).…”