Analysis of the spin-lattice relaxation rate and reorientational dynamics of fullerene C70 in chlorobenzene-d5

13C spin-lattice relaxation measurements were performed on C70 in deuterated chlorobenzene as a function of temperature and field strength to investigate the mechanistic nature of the relaxation process as well as to probe the rotational dynamics of this fullerene. Our measurements indicate that the chemical shift anisotropy (CSA) mechanism dominates the relaxation process up to a temperature of 323 K. At this temperature, the relaxation rates for all carbons are seen to switch directions indicating that the SR mechanism begins to dominate at higher temperatures. Experimental reorientational correlation times, τCeff, were used to obtain information on the diffusion coefficients, DZ and DX. Diffusion was observed to be anisotropic at the lower temperatures but progressed toward isotropic behavior with increasing temperature. Theoretical predictions generated by the Perrin and Hu-Zwanzig models were found to be significantly different than the experimental observations. The Gillen and Griffiths approach provided mixed success with DX predictions being close to experiment but DZ values being much higher than observed. An intuitive modification of the Giere-Wirtz model generated acceptable predictions to both diffusion constants suggesting that the reorientation of C70 can be correlated to the diffusion of spheroids whose effective rotational axes is represented by their molecular semi-axes.