Spin lattice relaxation of coupled spin 1–spin 1/2 system in anisotropic phases. Molecular dynamics of CHDCl2 in nematic phases

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Abstract
The general theory of the spin dynamics of the spin 1–spin 1/2 system is described. The normal mode equations for the spin lattice relaxation is established. The elements in the relaxation matrix are evaluated under the assumption that only intramolecular dipole–dipole interaction, quadrupole interaction, and intermolecular proton dipole–dipole interaction are important. The contributions from the interference term between the intramolecular dipole–dipole and the quadrupole relaxation has also been included. 1H and 2H spin lattice relaxation measurements have been performed on methylenechloride-d1 (CHDCl2) in two different nematic phases, Mercks phase V and ZLI 1167. Evidence for the existence of the interference effect between the dipole–dipole and the quadrupole relaxation has been found in both phases. The relaxation behavior is different in the two phases. The differences have been explained in terms of the ‘‘director fluctuation’’ theory.