The Third Virial Coefficients of Polar Gases

Abstract

The third virial coefficient is calculated for a gas composed of spherical molecules whose intermolecular potential has a repulsive term proportional to r⁻¹², an attractive term proportional to r⁻⁶, and which have point‐dipoles at their centers. The calculated values are compared with the experimental results for steam and ammonia, using parameters previously calculated from the second virial coefficient. The agreement is good for ammonia but poor for steam. It is suggested that this is because of the neglect of the higher multipoles in the interaction potential.