  In this paper we develop a thermodynamic perturbation theory for two site
associating fluids which exhibit bond cooperativity. We include both steric
hindrance and ring formation such that the equation of state is bond angle
dependent. Here the bond angle is the angle separating the centers of the two
association sites. As a test, new Monte Carlo simulations are performed, and
the theory is found to accurately predict the internal energy as well as the
distribution of associated clusters as a function of bond angle and bond
cooperativity.
