The spur model in polar solvents

1 The spur model in polar solvents (Strasbourg Group) [2] 

Based on a long series of experiments in polar solvents, the set of reactions shown below has been proposed (M and S stand for the medium and the solute, respectively). Some of the data that led to establish this model are presented in the following. 

Proper care must be taken in the presence of chemical equilibria (e.g., ion pairing or dimerization) as the free and associated species may have different inhibiting powers [10-12], 

At present, all positron scavengers have been found to belong to the class of partial inhibitors, and only a small portion of the electron scavengers. The reason for partial inhibition is still debated. 

Although limited, the decrease in I3 due to partial inhibition occurs at much lower solute concentrations (about 0.01—0.02 M) than that promoted by total inhibitors. This is reflected in the range of values for either type of inhibition constants in water, the highest k values are at about 20 M 1, while typical K values are in the range 40—140 M [2], By contrast with k, the partial inhibition constants are usually strongly temperature-dependent, with an activation energy close to that of the viscosity of the solvent [13]. 

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