Extended diffusion of a symmetric top molecule with internal rotation

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Abstract
Gordon’s extended J‐diffusion theory is used to calculate the reorientational correlation times and NMR spin–rotational relaxation rates of nuclei attached to a symmetric top molecule with internal motion. The molecular motions and lattice averages are calculated using classical mechanics. The exact classical solutions are used for the case where the internal rotation and molecular symmetry axes are coincident. However, for the other cases approximate solutions are derived which are valid when the moment of inertia of the internal rotor is much less than the moments of inertia of the whole molecule. The calculations include quantitative predictions for the variation of the correlation times and relaxation rates with the height of the barrier to internal rotation.