Influence of Multipolar and Induction Interactions on the Speed of Sound

Abstract

At large distances between molecules, the intermolecular forces are essentially attractive. They can be classified conveniently into three types, that is, multipolar, induction, and dispersion forces. We consider rigid nonlinear molecules with enough symmetry so those principal axes of the quadrupole tensor of the polarizibility coincide. Multipolar and induction interactions are calculated with the help of quantum mechanical calculations of the intermolecular energy function and the help of perturbation theory. The multipole expansion is terminated at the quadrupole term. The focus is on the development of a mathematical model for calculation of the influence of multipole and induction interactions on the speed of sound and other thermodynamic functions of state. For the calculation of the thermodynamic functions of state, perturbation theory with the Lennard-Jones potential as the reference is used. The thermodynamic and structural properties of the Lennard-Jones system are known from Monte Carlo and molecular dynamics computer simulations. All important contributions are featured (translation, rotation, internal rotation, vibration, intermolecular potential energy, and the influence of electron and nuclei excitation). The analytical results are compared with the experimental data and models obtained by classical thermodynamics and show relatively good agreement.