A Theoretical Model to explain the DNP Induced NMR Signals Using TEMPOL at 3.4 T
Dynamic nuclear polarization (DNP) is one of the most efficient methods to increase the sensitivity of NMR and MRI by transferring polarization from electron spins to nuclear spins. For radicals in solid solutions the nuclear signal enhancements during microwave irradiation are interpreted either using the thermal mixing (TM) mechanism or a combination of the solid-effect (SE) and cross-effect (CE) mechanisms. Although the SE and CE based analysis of the lineshape of the enhancement as a function of the MW frequency has been possible, it was only realized recently that these lineshapes are correlated to the electron polarization distribution in the sample. To quantify this correlation a theoretical model was introduced based that describes the electron spectral-diffusion (eSD) mechanism and its contribution to DNP through the new indirect-CE (iCE) mechanism.