From the reaction of OH radicals with aqueous alkyl iodides RI an outer charge-transfer (CT) complex (RI·OH) aq is formed which is in a rapid solvent assisted equilibrium with the inner CT complex (R + - IOH −) aq. Thereby, the alkyl iodide behaves as a dissociative donor and the OH radical as an associative acceptor. The corresponding transient absorptions, studied by pulse radiolysis of N 2O-saturated aqueous solutions, consist of an alkyl independent hand centered at 352 ± 2 nm due to the complexed IOH − ion and an alkyl dependent band varying from 310 to 323 nm for methyl to isopropyl iodide. The latter is assigned to the CT band of either the outer or the inner CT complex. Corresponding the extinction coefficient of the CT-band maximum for ethyl iodide (315 nm) is determined to be < 3000 ± 800 M −1 cm −1 or < 12000 ± 3000 M −1 cm −1 depending on the unresolved assignment to the outer or the inner complex. By detailed numerical computer simulation of the reaction mechanism with ethyl iodide the following rate data were derived. ▪ The rate constants for the outer complex decay, k(Etl − OH + Etl − OH), k(H + Etl − OH), k(OH + Etl − OH) and k(Et − + Etl − OH), which were assumed to be in a common ratio to the calculated diffusion controlled value, turn out to be diffusion controlled within experimental error, e.g., (6.0 ± 1.0) x 10 9, (1.6 ± 0.4) x 10 10, (6.0 ± 1.0) x 10 9 and (3.0 ± 0.5) x 10 9 M −1 s −1, respectively. For the outer ∞ inner complex equilibrium an equilibrium constant of K = 0.25 ± 0.05 was determined. Due to the existence of such equilibria, radical reactions in polar systems may cross over to ionic reactions. Polyiodomethanes also show comparable mechanisms. However CH 3Br,CF 3Br and CF 3I do not seem to form analogous inner complexes, probably due to higher ionization potentials.