Semiempirical Helium Intermolecular Potential. II. Dilute Gas Properties

Abstract

Parameter adjustments in a family of semiempirical potentials are reported. The result is a two-parameter potential incorporating theoretically determined dipole–dipole and dipole–quadrupole interactions which fits dilute helium gas data to within 6% over the temperature range 1–2000°K. The data fits near 50°K are not fully satisfactory, nor is the fit of viscosity data below 4°K. The sensitivity of the calculations to the inclusion of the dipole–dipole interaction for properties below 4°K is studied. The calculations using quantum mechanics show a greater sensitivity in the virial coefficient than the viscosity and differ from calculations using classical mechanics. The semiclassical limits of the calculations are discussed.