Dynamics of hydrogen bonding in an elementary model of water

The dynamics of the hydrogen bond breaking and reforming are investigated u sing a model for water in which each water molecule is a hard sphere with f our sticky spots located at the corners of a tetrahedron. H-bonding arises when a pair of particles attach at their sticky spots by means of the narro w, anisotropic square well potential. To escape the square well, and break the H-bond, a solvent molecule must collide with the bonded pair and commun icate sufficient energy along the line of centers so as to exceed the thres hold energy. The calculated time correlation function describes the fluctua tion in the number of H-bonded pairs. Its correlation time, associated with the three-body direct rupture, is roughly 0.83 ps in water at 300 K and ob eys an Arrhenius law. After bond rupture, the restituting solvent molecule can return (or backscatter) and in so doing, cause the initial dimer to ref orm its H-bond. As a result, the overall correlation time for bond breaking is roughly 14 ps. Employed here are aspects of the kinetic theory of squar e well fluids together with Wertheim's theory for associating systems. (C) 2001 American Institute of Physics.