Analytical treatment of the fused hard-sphere chain model. 0.5 < L < 1

Multidensity integral equation theory for a model of an associating fluid forming freely jointed fused hard-sphere chain, is presented. Our approach is based on the Wertheimʹs polymer Percus-Yevick (PPY) theory supplemented by the ideal chain approximation and can be regarded as an extension of the PPY theory for tangent hard-sphere fluids proposed by Chang and Sandler (J. Chem. Phys. 102, 1995, 437). The radial distribution function and the structure factor are calculated for the different model parameters. We compare the resulting predictions for the intermolecular distribution function with the Monte Carlo simulation results for the fused diatomic system. It is found that the accuracy of the prediction of the structure of such system is realiable in a rather wide range of density. It is shown that structure factor exhibits a peculiarity (so-called pre-peak) at small wave numbers, connected with the formation of relatively large molecular aggregates. The dependence of the pre-peak magnitude on the degree of penetrability is investigated and discussed.