Chemically induced multiplet electron-nuclear polarization in zero and low magnetic fields

We report the first observation of chemically induced electronic-nuclear multiplet spin polarization of transient radicals at very low and zero magnetic fields. Dimethoxyphosphonyl radicals, which have a hyperfine coupling constant of similar to70 mT, were produced in solution by photolysis of 2,4,6-trimethylbenzoyl phosphonic acid dimethyl ester. The radicals were detected using a modified L-band time-resolved electron paramagnetic resonance (TREPR) setup. The polarization is very strong, and signals are easily detected with custom-built resonators that match or nearly match each electronic-nuclear transition. A theoretical description for the formation of this large polarization has been proposed and is found to be in good agreement with experimental data. TREPR spectra and time-resolved kinetics at low and high magnetic fields have been measured. Signals detected at hi-h magnetic field decay an order of magnitude faster than do those at low field, which can be explained by field-dependent HFI-induced spin relaxation.