Measurements of total scattering cross section for various collision partners

Absolute values of total elastic cross sections were determined for argon scattered by 30 different aliphatic hydrocarbons, N2, O2, CO2, He and H2 at a relative velocity 555m/s. From these cross sections, the so-called van dar Waals C6 coefficients were determined for the attractive portions of the intermolecular potentials. Independent scattering measurements with 38 of these pairs indicated that the mixing rule values in general were within less than 5 percent of the experimental values. In addition C6 values calculated by the Slater-Kirkwood approximation were also found to be generally within about 5 percent of the experimental values except for hydrogen-hydrocarbon systems. A simple model was found to be effective in correcting the Slater-Kirkwood approximation for cases in which the molecular dimensions were an appreciable fraction of the internuclear distances.