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The spin-lattice relaxation time T1 and the spin-spin relaxation time T2 for two identical spins I=½ have been calculated for anisotropic reorientation in which the spin pair reorients randomly about an axis which, in turn, tumbles randomly. The results are applicable to liquids and solids provided that the correlation time for tumbling of the axis is small compared to T2. Although the two types of motion are independent, their contributions to relaxation are not. For nonviscous liquids, T1=T2. The results are generalized to multispin systems.
D. E. Woessner (Mon,) studied this question.