Model interpretations of the far infrared absorptions in compressed gaseous and liquid bromotrifluoromethane, CBrF3

Abstract

The far infrared (2–100 cm^–1) absorption of the symmetric top molecule bromotrifluoromethane (CBrF₃) has been measured for the gas phase in pressure range 1.2–46.2 bar and for the liquid. Whereas the peak of the broad bands observed moves only slightly from 9.8 cm^–1 at 1.2 bar to 11.0 cm^–1 in the liquid at the same temperature (295 K), there are pronounced differences in the bandshape which are reflected in considerable damping of the time functions obtained by Fourier transformation of the frequency data. A simple model of bimolecular collision induced dipolar absorption accounts fairly well for the high frequency shoulders which appear in the spectra of the compressed gas. Using this model, preliminary values of the quadrupole (Q) and octopole moment (Ω) of the molecule have been obtained. A mechanism of collision disturbed torsional oscillation of the permanent dipole (µ) within potential wells accounts more satisfactorily for the absorption in the liquid than the J-diffusion model, which assumes free rotation between instantaneous collisions.