Determination of the argon intermolecular pair potential by x-ray diffraction from the dense gas

The intensity distributions of x rays scattered by fluid argon were meausred at −100 °C and densities of 0.0824, 0.1331, 0.2087, and 0.3111 g/cm3. The experiment at 0.2087 g/cm3 was repeated to establish reproducibility. The structure factors measured at the three highest densities were Fourier transformed to obtain the direct correlation functions and the radial distribution functions. These functions were used along with the Percus–Yevick equation and a correction for three-body effects by Rowlinson to obtain four separate experimental estimates of the (state-independent) pair potential of argon. These four estimates were weighted by their precision and averaged to produce an optimal estimate of the pair potential, which has the characteristics ε=146.3±4.9 °K, σ=3.389 ±0.015 Å, and r0=3.86 ±0.05 Å. Quantities calculated from this potential are in reasonable agreement with the reported values for the second virial coefficient of argon and the transition energies of the argon dimer.