The second virial coefficient of planar dumb-bells

Abstract

A fluid whose molecules are pairs of hard discs can serve as a reference system for the study of adsorbed diatomic molecules. We obtain its second virial coefficient, point out an ambiguity in the definition of this coefficient when the separation of the centres of the disc exceeds √2 times their diameter, and compare the results with those for a capped rectangle, which is the equivalent hard convex body.