ANALYSIS OF THE REORIENTATIONAL MOTION OF C-60 IN TOLUENE-D8 AT 303-K

The C-13 spin-lattice relaxation time of buckminsterfullerene was measured in toluene-d8 at 303 K. The relaxation time was found to be 162 s, 8 times longer than previously estimated. Assuming the CSA mechanism dominates the relaxation process, the experimental T1 yielded a correlation time, tau(c), of 16.9 ps. Various hydrodynamic-based models were utilized in an attempt at duplicating this reorientational time. We found that the Stokes-Einstein-Debye (SED) model predicted a correlation time that was only a factor of 1.3 longer than the experimentally observed value. Surprisingly, other models (e.g. Gierer-Wirtz microviscosity, Hynes-Kapral-Weinberg, and free space model) predicted values that were approximately 4 times faster than the experimentally obtained value. By introducing a simple modification to the SED model, which we term the relative free volume model, we were able to duplicate, with a reasonable amount of accuracy, the experimental correlation time. Our modified model was then applied in a number of organic liquids, of varying viscosities and molecular properties, to predict the relaxation and reorientational times of C60 in these solvents.