ISOTOPE EFFECTS ON VAPOR PHASE 2ND VIRIAL COEFFICIENTS

W. Alexander Van Hook1, Luis P.N. Rebelo2, Max Wolfsberg3

1Chemistry Department, University of Tennessee, Knoxville TN 37996-1600 USA,
2Instituto de Tecnologia Quimica e Biologica, UNL, Apartado 127, 2780-901 Oeiras, Portugal,
3Chemistry Department, University of California Irvine, Irvine CA 92697-2025 USA

Vapor phase 2nd virial coefficient isotope effects (VCIE’s) are interpreted. A useful correlation is developed between -D(ß-bo)(ß-bo) = (-VCIE) and the reference condensed phase reduced isotopic partition function ratio [ln(fc/fg)]*. ß is the second virial coefficient, bo = 2ps3/3, s is the Lennard-Jones size parameter, and D 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(fcfg)]*.