Microviscosity Dependence of Magnetic Isotope Effect on Radical Pair Decay Rates in SDS Micellar Solution

The microviscosity dependences of the magnetic field and magnetic isotope effects on disappearance of radical pairs (RPs) comprising benzophenone ketyl and alkyl radicals were investigated in sodium dodecyl sulfate (SDS) micellar solutions. The increase in microviscosity of the SDS micelle by adding MgCl2caused not only a deceleration in the escape rate of the component radicals from the micelle but also a small magnetic isotope effect on the RP decay rate. The small magnetic isotope effect was explained by an increase in the correlation time of the radical motion, which is coupled with the anisotropic hyperfine interaction modulating the spin-lattice relaxation of RP.