Dielectric and Pressure Virial Coefficients of Imperfect Gases. I. Polar Halogenated Methanes

Abstract

Dielectric constants for the polar gases CFH3, CF3H, CClF3, and CCl3H in the range 50–143°C, and for CCl3F at 96.3°C, have been measured as a function of pressure and density in the pair interaction range of densities. Accurate values of dipole moment and polarizability of the first four molecules have been derived from the limiting temperature dependence at zero density, and dielectric and pressure second virial coefficients from the variation with density. The pressure coefficients are in good agreement with other compressibility data. The dielectric coefficients are very large and positive for CF3H, very large and negative for CFH3 and CClH3, and positive with approximately the values predicted for spherical polarizable dipoles in the case of CClF3 and CCl3F. The deviations from simple theory indicate major effects of molecular shape, but they are not satisfactorily explained by Buckingham and Pople's anisotropic short‐range pair‐potential model.