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