A quasielastic neutron scattering investigation of the van der Waals complex of benzene and hexafluorobenzene

Three phase transitions have been identified in the system C6H6 + C6F6, at 205, 251 and 274 K. We believe these phase transitions are the result of increasing amounts of orientational disorder in this material. The molecular dynamics of the lowest temperature phase have been studied in some detail and are shown to consist of sixfold reorientations of the molecule about its C6 axis. From the temperature dependence of this thermally activated reorientation we obtain Ea = -9·4 ± 0·5 kJ mol-1 and v 0 = 3·9 ± 0·6 meV (9·4 × 1011 Hz).