Statistical Mechanics of Linear Molecules. III. Hard-Core Model

Computations of the pair correlation functions have been carried out for model nonspherical molecules. The molecules were represented by two hard spheres with centers separated by a distance $R$ (“diatomic” model). The usual expansion of the correlation function in powers of the density was generalized to treat this problem and terms in the series up to and including those in (density)² were evaluated with the aid of the Percus–Yevick approximation. Both the angle‐dependent and the angle‐independent parts of the pair correlation function were computed for several values of the molecular length. These results were then used to calculate second, third, and Percus–Yevick fourth virial coefficients. The changes in pair correlation function, virial coefficients and equation of state were obtained as a function of molecular shape. It is shown that these changes are not large when compared to the hard‐sphere results using proper units; i.e., that the most important factor in these calculations is the alteration in molecular volume rather than in molecular shape.