Journal of Physical Chemistry, Vol.100, No.11, 4361-4364, 1996
C-13 Spin-Lattice Relaxation and Molecular-Dynamics of C-60 in 1,2-Dichlorobenzene-D-4
We have measured the C-13 spin-lattice relaxation rate of C-60 in 1,2-dichlorobenzene-d(4) and have found that the spin rotation (SR) mechanism contributes significantly to the overall relaxation process. The magnitude of SR was found to be smaller than in the solid phase but consistent with quantities projected for C-60 in toluene-d(8). These observations indicate that solvent effects play a critical role in determining the magnitude of the spin rotation contribution. Reorientational correlation times were also obtained experimentally and show that C-60 is undergoing rapid rotational motion in this solvent. The activation energy for this mode of motion was found to be 7.71 kJ/mol. Several theoretical models were employed in an attempt at characterizing the rotational behavior of the title molecule. Of these theories, the Gierer-Wirtz model proved superior in duplicating our experimental findings. The close agreement suggests that 1,2-dichlorobenzene-d(4) provides a discrete environment rather than a continuous one. Our study further indicates that C-60 reorients in the "slip" limit where solute-solvent interactions are at a minimum.