Infrared intensities: A model for the quantitative prediction of the vibrational strengths of SF6 and UF6

Abstract

Using an atomic polar tensor for the F atom obtained from an analysis of the experimental infrared intensities of CH₃F and normal coordinate analyses of SF₆ and UF₆, the infrared spectra of SF₆ and of UF₆ have been predicted and compared with experiment. The absolute infrared intensities predicted for the infrared‐active fundamental vibrations of SF₆ agree quite well with experimental values; for UF₆, the experimental values are less well‐determined, but the agreement also appears to be satisfactory. The intensities of the binary combination bands have also been calculated, using anharmonic force constants introduced by the use of curvilinear coordinates supplemented by terms in the valence‐bond stretching coordinates estimated from an assumed Morse potential, and using the calculated intensities for the fundamentals neglecting electrical anharmonicities. These predictions also appear to be in semiquantitative agreement with the experimental data.