Sezer, Deniz. “Dynamic View of the Solid-State DNP Effect.” Preprint. Hyperpolarization/Theory, March 6, 2023.
https://doi.org/10.5194/mr-2023-1.
The first report of dynamic nuclear polarization (DNP) in liquids via the solid-effect mechanism [Erb, Motchane and Uebersfeld Compt. rend. 246, 2121 (1958)] drew attention to the similarity between the field profile of the enhancement and the dispersive component of the EPR line. The implications of this similarity, however, were not pursued subsequently as practically at the same time Abragam explained the effect in terms of state mixing by the dipolar interaction. Here we 5 develop a description of the solid effect which is grounded in the dynamics of the electron-nucleus spin system, rather than the static view of state mixing. Our approach highlights the role of the coherences in the polarization transfer, and shows that the offset dependence of the DNP enhancement can be rationalized as the response of two band-pass filters connected in series. The first filter is the power-broadened EPR line; the second filter consists of two parts centered on both sides of the electronic resonance and displaced by one nuclear Larmor frequency from it. Being proportional to the product of the two filters, the DNP 10 enhancement profile acquires its odd symmetry from the dispersive EPR line, as intuited by Erb et al. and in agreement with their phenomenological treatment. The developed time-domain description of the solid effect is extendable to liquids where the dipolar interaction changes randomly in time due to molecular diffusion.