The diffusion of radon gas mixtures

Abstract

The repulsive force, F 12 , between dissimilar molecules may be represented by the equation F 12 = μ 12 d - 8 12, where d is the distance between the dissimilar molecules which are regarded as point centres of repulsive force, while 8 12 represents the repulsive force index, and μ 12 the repulsive force constant between these molecules. Chapman (1929) has given a special theory of thermal diffusion in mixtures of two gases in which one component is rare and heavy. He has shown that F 12 may be determined provided that thermal diffusion measurements for the given gas mixture have been made, and the coefficient of viscosity of the lighter gas at various temperatures together with the coefficient of diffusion of the two gases is known. Thermal diffusion measurements for radon-hydrogen and radon-helium gas mixtures have already been made by one of us (Harrison 1937), radon being the rare and heavy constituent of these mixtures. The variation of the viscosity of hydrogen and helium over a wide range of temperature was known, but no experimental value of the coefficient of diffusion of radon into hydrogen or helium was available. In the previous investigation, approximate values of the latter were therefore calculated from a formula given by Chapman (1917). Owing to uncertainty in the accuracy of these calculated values, 8 12 was evaluated approximately for radon-hydrogen and radon-helium molecules, but μ 12 was not calculated, since the latter is much more sensitive to an error in the coefficient of diffusion than the former. The purpose of the present investigation was to obtain experimental values of the coefficient of diffusion of radon into hydrogen, helium, neon and argon, so that the repulsive force between radon-hydrogen and radonhelium molecules can be derived from existing experimental evidence, and that for radon-neon and radon-argon can be obtained when the thermal diffusion measurements for these two mixtures are completed. Information concerning the very massive, monatomic radon molecule obtained from diffusion experiments is of special interest, particularly as the molecular field cannot be obtained from viscosity measurements or the equation of state owing to the extremely small quantity of gas available.