Non-ideality of an ‘‘ideal ’’ liquid mixture: (36Ar+40Ar)

Abstract

A mixture of two isotopes of the same rare gas represents the extreme case of molecular simplicity. In this work, the excess molar Gibbs energies for liquid mixtures of (³⁶Ar+⁴⁰Ar) have been m easured for the first time, with unprecedented precision. Results show that the excess vapour pressure of an equimolar mixture is approximately 2.5 Pa in the 85–96 K temperature range. The results are well predicted by a modified version of the quantum theory of isotope effects in mixtures.