Model of a Reacting Liquid

The microscopic description of a chemically reacting fluid depends to a considerable extent on the specific chemical reaction under consideration. To present the kinetic theory results in a manner that is not purely formal, we focus primarily on a particular class of models that should be appropriate for several types of reaction. We provide some physical background for these models and then turn to their mathematical description. 

A simple model that corresponds to a reaction with these foregoing characteristics can be constructed along the following lines. We suppose that the internal states of reactant and product molecules can be treated in a average way by assigning effective one-level internal energies to them. Then, for 

This type of model is not especially appropriate in all situations, however—for example, the atom recombination process. The relevant potential energy surface for this process was shown in Fig. 4.1. We noted in Section IV that there are no large chemical barriers for the recombination, and the details of the strongly attractive forces play an essential role in the reaction dynamics of this system. A theoretical treatment of this reaction must therefore include this direct chemical force, since it will play an essential role in governing the dynamics of the approach of the atoms through the solvent. We shall defer a thorough discussion of this case to Section XII, where the atom recombination problem is discussed in more detail, but the kinetic theory is formulated in a way that permits this case also to be studied. 

Any fully microscopic theory of condensed-phase reactions must also specify the nature of the solute-solvent and solvent-solvent forces. Once 

We also adopt a similar description for the solvent. This type of model requires some comment, even when applied to the simple solvents such as dense liquid argon or other noble gases. Although the static structural properties of such fluids are represented quite well by taking into account only the strongly repulsive parts of the potential, the weak attractive forces do have noticeable effects on dynamic properties such as the velocity autocorrelation function.However, a model that includes only the repulsive forces is not unreasonable for a description of the solvent dynamics in dense liquids, and this expedient is adopted. We focus on general features that are not expected to be especially sensitive to this approximation. 

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