EVIDENCE FOR THE BREAKDOWN OF THE POINT MULTIPOLE APPROXIMATION FROM FAR-INFRARED STUDIES ON LIQUID FLUORINATED BENZENES

Attempts to explain the observed liquid phase far-infrared intensities of benzene, hexafluorobenzene and 1,3,5-trifluorobenzene in terms ofpointquadrupole-induced dipole interactions result in failure to account for the extremely different absorption strengths. We consider the possible sources of (gross) error in this (simple) approach and conclude that the use of distributed charges to compute site-site interactions (including short ranged attractive (CT) forces) would be necessary in order to predict such spectra for non-polar molecules. The power of far-infrared absorption spectroscopy in studying short ranged "ordering" and dynamics in liquids is emphasised. © 1990.