On nuclear magnetic relaxation due to slow molecular reorientation and fast internal rotation interference

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Abstract
Spin-lattice relaxation arising from modulation of the dipole-dipole interaction by slow molecular motion together with fast internal rotation interference is investigated. The magnetic interaction for the internal rotation is treated as a perturbation and a modified stochastic Liouville equation, which is exact in all orders of the residual perturbation for the overall reorientation of the molecule, is derived after averaging over the internal rotation modes. The resultant equation is solved by the eigenfunction expansion method to study the spin-lattice relaxation. Results show complicated damping oscillations which Donskaya's work has failed to predict. Such oscillations in the relaxation are found in the slow motion region. Effects due to jump diffusion and brownian diffusion in the internal rotation are also considered.