Diffusion-limited rate constant Debye theory

The first of the theoretical chapters (Chapter 9) treats approaches to the calculation of thermal rate constants. The material is familiar—activated complex theory, RRKM theory of unimolecular reaction, Debye theory of diffusion-limited reaction—and emphasizes how much information can be correlated on the basis of quite limited models. In the final chapt, the dynamics of single-collision chemistry is analyzed within a highly simplified framework the model, based on classical mechanics, collinear collision geometries, and naive potential-energy surfaces, illuminates many of the features that account for chemical reactivity. 

It can be seen from the table that the predictions of the Debye-Smoluchowski theory are as follows, (i) The formation and dissociation of an encounter-complex involving uncharged species is always a very rapid process, (ii) In solvents of high dielectric constant, such as water, charges have little effect on the rates, but in media of low dielectric constant both rate and equilibrium constants are drastically affected, (iii) In aprotic solvents of intermediate dielectric constant, the diffusion apart of ions is a slow process, and may be rate-limiting in an overall proton-transfer reaction, (iv) In media of low dielectric constant, free ions are not formed at the usual concentrations. In what follows, several of these predictions are used and tested in the interpretation of experimental data. 

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