Cage effects, correspondence between

In this case of uncharged, nonpolar reactions, there is little interaction between the reactants and the solvent. As a result, the solvent does not play an important role in the kinetics per se, except through its role in determining the solubility of reactive species and cage effects. The rate constants for such reactions therefore tend to be similar to those for the same reactions occurring in the gas phase. Thus, as we saw earlier, diffusion-controlled reactions in the gas phase have rate constants of 10-ll) cm3 molecule-1 s-1, which in units of L mol-1 s-1 corresponds to 6 X 1010 L mol-1 s-1, about equal to (usually slightly greater than) that for diffusion-controlled reactions in solution. 

If the external surface contains sites similar to those in the cages, radical reaction could occur more effectively because of better accessibility of the gas phase. However, I doubt that an irregular external surface could hold Co2+ in surface positions because of the tendency of Co2+ to find tetrahedral or octahedral positions. The present spectra, of course, show only complexes formed on internal surfaces because there is a linear correspondence between the absorption coefficient and concentration and because all ions observed on Type A are surface ions. 

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