Accurate “Effective” Intermolecular Pair Potentials in Gaseous Argon

The “effective” intermolecular potential in gaseous argon has been determined, accurate through first order in density, for various assumed argon–argon potentials and the triple‐dipole interaction. This potential should lead to the correct radial‐distribution function. The calculations do not agree with the 1965 analysis of experimental data by Mikolaj and Pings [Phys. Rev. Letters 15, 849 (1965) ]. Our results suggest a density dependence of the minimum of the effective potential of only about 17 $\mathrm{\rho ̄}$ (in degrees Kelvin), where $\mathrm{\rho ̄}$ is the density in grams per cubic centimeter. This constant has a sizeable temperature dependence but only a small variation proportional to density. The contribution of other nonadditive effects is briefly examined as is the small contribution of nonadditive effects to the x‐ray structure factor of the liquid.