Chapter 11 - Molecular Liquids

Abstract

Earlier chapters are concerned almost exclusively with atomic liquids, for which the interactions between particles are spherically symmetric. Here the methods already developed are extended to molecular liquids, where allowance nust be made for the presence of orientational degrees of freedom. This generalisation leads to complications that are largely technical in nature. In particular, molecular pair distribution function now depends on the mutual orientation of two molecules. An alternative representation of the liquid structure is one based on radial, site-site distribution functions. The case of dipolar liquids is discussed first and the relationship between pair correlation functions and the dielectric constant is established. Diagrammatic expansions are adapted to deal with site-site interaction models and the resulting reference interaction-site model (RISM) theory is analysed; related theories are applied to associating liquids. Approximations for certain reorientational time correlation functions are derived.