Application of integral equation joined with the chain association theory to study molecular association in sub- and supercritical water

In this report, the Percus-Yevick and the Omestein-Zernike integral equatio ns are solved simultaneously for the radial distribution functions of water at various state conditions, including sub- and supercritical states. The intermolecular potential function used in this study consists of an effecti ve Kihara potential, which is derived for associated fluids. For derivation of the effective potential function, water is considered as a mixture of a ssociated species due to hydrogen bonding. The contribution of hydrogen bon ding is considered in the formulation of the effective Kihara potential par ameters through the application of the analytic chain association theory. T here is a good agreement between the present calculations and the experimen tal data in predicting the oxygen-oxygen radial distribution function near the critical point and at supercritical conditions for which experimental d ata are available. It is also concluded that at supercritical conditions a considerable degree of hydrogen bonding may be still present in the form of linear chain association. Therefore, the chain association model is valid near the critical point and at supercritical. conditions instead of other s tructure models for the investigations on molecular structure of water.