Diffusion in organic liquids. Part 2.—Isotope-mass effects in self-diffusion in benzene and cyclohexane

Abstract

Using the diaphram cell and gel sectioning techniques, the existence of significant isotope-mass effects in self-diffusion has been confirmed for the organic liquids benzene and cyclohexane in the temperature range 280–313 K. The former shows a small but significant mass effect of the expected sense [D(lighter isotope) > D(heavier isotope)] which is constant and independent of temperature. The latter liquid shows no mass effect at the lower end of the temperature range but a reversed mass effect at higher temperatures. This surprising distinction is not predicted by any existing empirical or theoretical model for diffusion in the liquid state.