Deuterium spin relaxation and spectral densities in the liquid crystal 4-n-pentyloxybenzylidene-4′-n-heptylaniline-2, 3, 5, 6,-d4

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Abstract
We report on the measurements of the deuterium Zeeman and quadrupolar spin‐lattice relaxation times and the deuterium spin–spin relaxation time in the nematic, smectic A and C phases of a ring‐deuterated 4‐n‐pentyloxybenzylidene‐4’‐n‐heptylaniline. The spectral densities of motion J0(0), J1(ω0), and J2(2ω0) at ω0/2π=14.73 MHz were separated from the above relaxation times. A simple ‘‘rotational diffusion in a cone’’ model was used to account for the observed increase in J1(ω0) and the decrease in J2(2ω0) in the nematic phase as the temperature was decreased. The model of rotational diffusion in a restoring potential was also examined. Our data can be understood qualitatively using the strong collision model or semiquantitatively using the cone model. The restricted rotational diffusion in a cone model supports the molecular reorientations being in the intermediate motion regime (ω0τ≂1). Additional information on Jp(ω) such as its frequency dependence are required to check the various assumptions used in the above motional models.