Comment on mr-2023-2

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> The solid-state effect of dynamic nuclear polarization (DNP) is operative also in viscous liquids where the dipolar interaction between the electronic and nuclear spins is partially averaged. The proper way to quantify the degree of averaging, and thus calculate the efficiency of the effect, should be based on the time-correlation function of the dipolar interaction. Here we develop a general theoretical description which can take different dipolar correlations functions depending on the assumed motional model. At high magnetic fields, the theory predicts DNP enhancements at small offsets, far from the classical solid-effect positions that are displaced by one nuclear Larmor frequency from the electronic resonance. The predictions are in quantitative agreement with such enhancement peaks observed at 9.4 T [Kuzhelev et al. <em>JACS</em>, <strong>144</strong>, 1164 (2022)]. These non-canonical peaks are not due to thermal mixing or the cross effect but exactly follow the dispersive component of the EPR line.