Observation of radical pair zero quantum coherence effects in the FT-EPR spectra of SO3− and eaq− generated by photoionization of sulfite ions

The time evolution of the intensities of FT-EPR signals from the hydrated electron (eaq−) and SO3− radical formed by photoionization of SO32− in aqueous solution shows an oscillatory pattern. The effect is attributed to the coherent S–T0 spin state evolution in the [eaq−⋯SO3−] radical pair producing spin polarization in the free radicals. The damping of these oscillations is not as strong as that predicted by the radical pair mechanism (RPM) chemically induced dynamic electron polarization (CIDEP) theory formulated by Adrian [Chem. Phys. Lett. 272 (1997) 120]. The experimental data can serve to test alternative theoretical descriptions of RPM CIDEP in terms of coherent radical pair spin state evolution combined with diffusive motion of the radicals.