Intermolecular potentials from transport and thermodynamic data: role of the molecular vibrations on the example of CF₄

Abstract

Vibrationally excited states of spherically symmetric molecules have larger collisional diameters compared with the ground state. Molecular gases are mixtures of different excited states in different vibrational modes. Therefore the concept of a single potential of interaction between two molecules fails to describe both transport and thermodynamic properties simultaneously. A model of a gas with slightly different interactions between vibrational states is proposed. It agrees with experimental data well within the corresponding errors. As an example CF4 is considered and the model proposed here describes fairly well 87 experimental points. The alternative model of a single potential leads to a RMS which is factor of three larger and on average exceeds by two times the accepted experimental errors.