Self-Diffusion and Impurity-Controlled Proton Relaxation in Liquid Methane

Abstract

Self‐diffusion in liquidmethane, under its own vapor pressure, has been studied between the triple point and the normal boiling point by means of the spin‐echo technique. The activation energy for self‐diffusion is approximately 0.67 kcal/mole. These results are compared with the constant‐pressure tracer results of Naghizadeh and Rice [J. Chem. Phys. 36, 2710 (1962)], which show somewhat higher (∼15%) self‐diffusion coefficients and an activation energy of approximately 0.83 kcal/mole. The temperature dependence of self‐diffusion in liquidmethane appears to be comparable on the basis of a classical reduction to corresponding states, by means of critical constants, to that in liquid Ar, Kr, and Xe. Measurements of the proton spin‐lattice relaxation time in our sample indicate that the relaxation is predominantly controlled by the mutual diffusion of the hydrocarbon and small amounts of dissolved oxygen.