The character of the far infra-red absorptions in non-polar liquids

Using Fourier spectrometry submillimetre absorption. and in some cases refraction. spectra have been observed for a number of liquids. The molecules chosen have small or zero permanent electric dipole moments: cyclohexane C6H12. dimethylacetylene C6H6, 1-octyne C8H14, 1,4-dioxan C4H8O2, benzene C6H6, carbon tetrachloride CCl4, carbon disulphide CS2 and cyclohexene C6H10. The observed absorptions are greater the greater the polarity of the molecules or the lower the rigidity and symmetry of the molecular structure. A translational-vibrational (collisional) origin is suggested for the attenuation in the non-polar systems.