ELECTRON-SPIN EXCHANGE IN MICELLIZED RADICAL PAIRS .3. C-13 LOW-FIELD RADIO-FREQUENCY STIMULATED NUCLEAR-POLARIZATION SPECTROSCOPY (LF SNP)

LF (low-field) SNP spectra are reported from the carbonyl carbon in dibenzyl ketone photolyzed in an aqueous micellar solution with sodium dodecyl sulfate. Spectra obtained using resonant radiofrequencies of 0.33 and 1.53 GHz are affected by adiabatic transitions within the region of ST- level-crossing of the radical pair and by flip-flop transitions in the corresponding weak magnetic fields. Numerical simulation indicates that all the observable features of the spectra are accounted for by a combination of these transitions and spin relaxation induced by the electron spin exchange interaction. Unexpectedly, no additional broadening caused by the electron dipole-dipole or other anisotropic interactions is evident in them.