NMR observations of molecular motions and Zeeman-quadrupole cross relaxation in 1,2- difluorotetrachloroethane

We report measurements of "F NMR relaxation times Tu Tlf, TID, and T2 in the plastic crystal CFCL2-CFCL2 . From the data near the melting point, we obtain the jump time for translational selfdiffusion. At lower temperatures, we observe on the cold side of the T, and Tif minima an unusual field dependence which is substantially less than the normal field-squared dependence. We also observe a reduction in T\ near 40 MHz due to cross relaxation between the Zeeman levels of the "F spins and quadrupole levels of the 3 5C1 and 3 7C1 spins. We measured the cross relaxation times TIS as a function of field and found good agreement with our theoretical calculation of TIS.