Vapor Pressures of Isotopic Krypton Mixtures. Intermolecular Forces in Solid and Liquid Krypton

The vapor pressures of normal krypton and a krypton sample containing 50% 80Kr have been measured from 94 to 130°K. New vapor pressure equations are derived for solid and liquid normal krypton. The triple-point pressures and (temperatures) of 80Kr and 84Kr are 547.565 (115.77) and 547.502 (115.78) int. mm Hg (°K), respectively. The triple-point pressure of normal krypton is 547.52 ± 0.10 int. mm Hg. The reduced partition functions, fc/fg, of 84Kr/80Kr have been derived for the solid and liquid from the vapor pressure data. The solid data lead to a θ0 (D) = 71.8°K in excellent agreement with heat capacity data. The change in ln (fc/fg) on melting is found to be 24% in good agreement with previous results on neon and argon. V 〈 ∇2 U 〉 is derived from the experimental values of ln (fc/fg) in the liquid. The repulsive potential in liquid krypton is less steep than that in neon or argon. Calculations of V 〈 ∇2 U 〉 from neutron scattering measurements show that the exp-6 potential to be superior to the LJ (12, 6) potential for liquid krypton. A corresponding states analysis through 〈 ∇2 U* 〉 leads to a quantitative correlation of the solid and liquid phase (fc/fg) data for Ne, Ar, and Kr.