Assignments in the ultraviolet spectra of MoF6 and WF6

Abstract

The ultraviolet absorption spectra of gaseous MoF₆ and WF₆ were measured from 1100 to 2500 Å (40 000–90 000 cm⁻¹). Assignments of the observed transitions, based on a qualitative molecular orbital diagram and comparisons of predicted and observed relative band intensities, are proposed. The ligand field splitting of the Mo(4)d orbitals is estimated to be 40 000 cm⁻¹. A comparison of the uv absorption and photoelectron ionization spectrum of WF₆ suggests that for this molecule the ligand field approximation is excellent: There are no interactions between the ligand and metal orbitals. Many of the observed transitions manifest progressions in the a₁ vibrational mode from which expansions of the molecular octahedron in each of the assorted electronic excited states is deduced.