Lattice defects in plastic organic crystals. Part 7.—Isotope mass effects in self-diffusion in cyclohexane

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Abstract
A study has been made of the diffusion of the species 12C5 14C1 1H12 and 12C6 2H11 3H1 in single crystals of cyclohexane at 242 K. The measured diffusion coefficients are in good agreement with previously published values. An estimate of the isotope mass effect yields a value of the mass factor Ea b= 0.003 ± 0.004. This virtually-zero value indicates that self-diffusion in cyclohexane proceeds by a complicated mechanism in which many molecules are involved ( >12). This discovery confirms previous speculations on the defect structure of the low entropy of fusion plastic solids.