The second and third virial coefficients of simple fluids

The asymptotic behavior of the second $B$ and third $C$ virial coefficients in the low temperature region is analyzed for fluids with a spherical pair-additive potential of interparticle interaction. The temperature dependences $B(T)$ and $C(T)$are approximated by expressions which convey correctly the behavior of the virial coefficients in the low-and high-temperature limits. The free parameters of approximation formulas for pure nitrogen, argon, and oxygen are determined. The derived virial equations of state are used to calculate the limit of significant instability of the gas phase in a wide temperature range.