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

Abstract

A study has been made of the diffusion of the species ¹²C₅¹⁴C₁¹H₁₂ and ¹²C₆²H₁₁³H₁ 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 E^a_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.