Vapor phase 2nd virial coefficient isotope effects (VCIE's) are interpreted. A useful correlation is developed between -Δ(ℬ-bo)/(ℬ-bo) = (-VCIE) and the reference condensed phase reduced isotopic partition function ratio [ln(fc/fg)]*. ℬ is the second virial coefficient, bo = 2πσ3/3, σ is the Lennard-Jones size parameter, and Δ is an isotopic difference, light-heavy. [ln(fc/fg)]* can be obtained from vapor pressure isotope effects for T/TCRITICAL < 0.7. Also (-VCIE) = ln(fp/fg2), where ln(fp/fg2) is the reduced isotopic partition function ratio describing the equilibrium between monomers and interacting pairs. At temperatures well removed from crossovers in ln(fp/fg2) or [ln(fc/fg)]*, ln(fp/fg2) = (0.4±0.2) [ln(fc/fg)]*.
- Isotope effects
- Lennard-Jones potential
- Reduced partition function ratio
- Vapor phase
- Vapor pressure isotope effects
- Virial coefficients