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>Threehyphen;Body Quantum Correction to the Free Energy of a Simple Liquid and the Role of Pair and Triplet Potentials in Isotopic Distillation
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Threehyphen;Body Quantum Correction to the Free Energy of a Simple Liquid and the Role of Pair and Triplet Potentials in Isotopic Distillation
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机译：Threehyphen;Body Quantum Correction to the Free Energy of a Simple Liquid and the Role of Pair and Triplet Potentials in Isotopic Distillation
The lowesthyphen;order quantum correction to the partition function and free energy of a simple dense fluid is generalized to take account of manyhyphen;body forces. The threehyphen;body quantum correction is calculated using the triplehyphen;dipole potential for the nonadditive interaction, assuming the superposition approximation for the triplet correlation function, and taking the pair correlation functions from x ray and neutron diffraction experiments. In the case of liquid Ar near the triple point, the threehyphen;body correction is small enough to be neglected in connection with isotopic distillation experiments. These experiments provide values forlang; nabla;2U rang;, whereUis the total interaction energy of the molecules in the liquid, and the results can be used in conjunction with experimental radial distribution functions to test empirical pair potentialsu(r) for the Armdash;Ar interaction. Several forms ofu(r) are investigated and the Barkermdash;Pompe, Kingston, and (exphyphen;6) potentials are found to give the best results forlang; nabla;2Urang;. The values oflang; nabla;2U rang;test the repulsive region of the potential and are much less sensitive to the form ofu(r) than is the vapor pressure of the liquid near the triple point. The vaporhyphen;pressure and isotopichyphen;distillation tests are compared.
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