Calculation of thermodynamic isotope effects of simple fluids by means of quantum corrections and isotope-induced differences in potential parameters

Formulas are given for thermodynamic isotope effects of simple fluids treated as hard-sphere and square well systems. A special method, the micropotential method, is used for calculating classical thermodynamic functions. Quantum corrections related to these functions are also given. Isotope effects due to the variation of the total mass (mass effects) are represented by calculating the changes of the quantum corrections of thermodynamic functions. Isotope effects caused by variations of the potential parameters (potential effects) are presented for methane. They are of the same order of magnitude as the corresponding mass effects. (author)