For the measurement of (1/T ZF 1 ) at zero field in Fig. , the field provided by the Helmholtz coil was brought down to zero within 50 ms, which was experimentally tested to ensure an adiabatic transfer to zero field. This adiabaticity ensures that the population of the Zeeman states are converted into populations of the zero-field eigenstates. After a variable time τ at zero field, a pulse of 470 µT and 100 µs duration was applied along the same axis, corresponding to a 4π-and π-pulse on proton and carbon spins, respectively. This pulse yields the max- imum signal according to Eq. A16. In Fig. the NMR signals for the T 2 measurements were obtained after rapid field-drop and signal acquisition at zero field. Additionally, the stacked NMR signal is shown under the pulse sequence, broadening with increasing radical concentration.