Triplet Potential for Argon

Abstract

Third virial coefficients, recalculated from $\mathrm{pVT}$ data, are used to determine the term in the effective argon pair potential which is linearly dependent on density, namely the averaged triplet potential. This potential is assumed to be of the form ${\mathrm{-\hspace{0.17em}a(T)r}}^{\mathrm{-n}}{\mathrm{\hspace{0.17em}+\hspace{0.17em}b(T)r}}^{\text{−6}}$ , where $\mathrm{b(T)}$ is derived from the known triple dipole interaction energy at large distances. Expressions for $\mathrm{a(T)}$ are empirically deduced for $n$ equals 12, 18, and 24, and the resulting potentials are compared with the pair potential. Nonadditive contributions from this averaged triplet potential to the higher virial coefficients are shown to be small.