Viscosity and polar-nonpolar interactions in mixtures of inert gases with ammonia

The viscosities of the binary gas mixtures He-NH₃, Ne-NH₃, Kr-NH₃ and Xe-NH₃ have been measured by the oscillating-disc method in the temperature range from -35°C to 35°C. The experimental data are systematically higher than the calculated values obtained by using the conventional combination rules for the parameters of the interaction potential for the polar-nonpolar interaction which includes the dipole-induced dipole term only. The discrepancy increases from He to Xe. These results are consistent with those obtained previously for mixtures of CH₃Cl gas with the inert gases. It has been suggested that the major cause of the discrepancy is the neglect of the r⁻⁷ term in the interaction between a polar and a nonpolar molecule.