Hydrogen-bond network rearrangement dynamics

In the preceding section, we discussed the equilibrium aspects of the percolating network of extended hydrogen-bonding in liquid water. We now discuss the dynamics of the rearrangement of this network. 

At room temperature, these HBs can break and re-form quite rapidly, leading to the rearrangement of the network. At the microscopic level, we need to understand the lifetime and bond-breaking mechanism of individual HBs between two neighboring water molecules. In the case of a water molecule, such bond-breaking events lead to the spatial/rotational displacements that in turn lead to the translational and rotational diffusion of water molecules. Therefore, the basic mechanism of the microscopic dynamics in water is expected to be different from a simple liquid made of nearly spherical units, Uke in the case of argon. 

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I. Ohmine and S. Saito,Water dynamics fluctuation, relaxation, and chemical reactions in hydrogen bond network rearrangement. Acc. Chem. Res., 32 (1999), 741. 

Saito, S., Ohmine, I. (1998). Off-resonant fifth-order nonlinear response of water and CS2 Analysis based on normal modes. J. Chem. Phys. 108 240-251 Saito, S., Ohmine, I. (1999) Water dynamics Fluctuation, relaxation, and chemical reactions in hydrogen bond network rearrangement. Acc. Chem. Res. 32 741-749. 

Fig. 4. Schematic representation of the observed dynamics. Initially uncomplexed photoacid first forms an encounter complex through diffusion. This loose complex either rearranges to a tight complex, or reacts via the hydrogen bonded network between photoacid and base. A pre-formed photoacid-base complex can directly react with extremely fast rates.

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