The predicted infrared spectrum and the structure of the isolated UF5 molecule

Abstract

The infrared absorption spectrum by the fundamental modes of UF5 is calculated using force constants transferred from UF6 to predict the wavenumbers and using the F atom polar tensor from CH3F to predict the intensities. Calculations are made for several assumed geometrical configurations of UF5. Comparison of the predicted spectra with the recently observed spectrum, in the UF-stretching region, of a photolysis product of UF6 isolated in an Ar matrix suggests strongly that the structure is square pyramidal (C4v) with the U atom above the F atom equatorial plane. Although the model for the intensities is simple, the calculated spectrum is expected to predict the correct order of magnitude of the intensities of the fundamentals, first overtones, and binary combination bands of UF5, and the approximate wavenumbers for the expected absorption. Some comparisons are given between the calculations for the several structures of UF5 and observed spectra of other XF5 molecules, including PF5, BrF5, and IF5.