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

Abstract

Self-diffusion in liquid methane, 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 liquid methane 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.