Self-Diffusion Coefficients and Rotational Correlation Times in Polar Liquids. II

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Abstract
Self‐diffusion coefficients and rotational correlation times have been measured in several polar liquids by pulsed nuclear magnetic resonance techniques. Self‐diffusion coefficients are reported for CH3OH, CH3NO2, (CH3)2CO, C6H5NO2, and C6H5Cl; proton, deuterium, and chlorine‐35 relaxation times are given for these liquids. Deuteron quadrupolar coupling constants for the deuterated molecules were measured directly for the solids at low temperature. Methyl groups in CH3OH, CH3NO2, and (CH3)2CO have correlation times that are considerably shorter than the correlation time for the tumbling of the entire molecule. The Ivanov theory of large amplitude molecular jumps is generalized to the case of two kinds of jump about different axes and an explicit expression for the over‐all correlation time is given. The pre‐exponential factors of the methyl group correlation times appear to change drastically in CH3OH and CH3NO2 upon melting. Rotational correlation times for molecular tumbling are in good agreement with those calculated from quasilattice random flight model. In methanol there is evidence that rotation of the molecule about the OH bond direction occurs more rapidly than the over‐all tumbling of the molecule. Molecular rotation also appears to be anisotropic in nitrobenzene as evidenced by a factor of 2 difference between the nitrogen and deuteron rotational correlation times. The pressure dependence of the intramolecular relaxation rate in C6H5Cl reported by Bull and Jonas is also shown to be in reasonable agreement with the prediction of the quasilattice model.