Deuterium relaxation of a partially oriented methyl group. III. Order director fluctuations and solute reorientation in a nematic solution of acetonitrile-d3

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Abstract
Deuteron spin‐lattice relaxation rates (R1Z) and relaxation rates of quadrupolar order (R1Q) have been determined between 13 and 47 °C at 38.4 MHz, for a 10.5 mol % of acetonitrile‐d3 in Merck Licristal phase 5, and selective and nonselective measurements of spin‐lattice relaxation have been carried out at 4.6 and 9.2 MHz over the same temperature range. The data can be satisfactorily explained by a combination of fast, anisotropic reorientation (corrected for effects of static ordering) and hydrodynamic fluctuations in the orientation of the nematic director. Large values of the rotational anisotropy were derived from the spin‐lattice relaxation data, and confirmed by 38.4 MHz measurements of the temperature dependence of the relaxation rate R2(ZQ) of a zero quantum coherence. The results obtained here are discussed in terms of recent related 13C relaxation studies of acetonitrile in nematic solution.