TEMPERATURE-DEPENDENCE OF REORIENTATIONAL DIFFUSION IN HEXAFLUOROBENZENE

Raman bandwidths of the C-F stretching [nu1(a1g) and nu15(e2g] and ring stretching [nu2(a1g) and nu16(e2g] vibrational modes of hexafluorobenzene were analyzed as a function of temperature in the liquid phase. Values of the perpendicular ('tumbling') diffusion coefficients, D(perpendicular-to), calculated from nu2 agreed well with earlier reports in the literature. It was determined that both of the e2g vibrational bandshapes were artificially broadened by the presence of closely lying combination modes superposed upon the bandshapes of the fundamental vibrations. Following decomposition of the bands into their individual components, the parallel ('spinning') diffusion constants, D(parallel-to), calculated from nu15 and nu16 were in excellent agreement with each other at all temperatures, and also agreed quite well with values of D(parallel-to) predicted by the Free Rotor model of molecular reorientation.