Fig. 2.

Selected ESR lineshapes of the spin probe TEMPOL in quenched bulk water and subsequent reheating at the indicated temperature. Note that: (i) for technical convenience the static magnetic field B₀, and not the microwave frequency ω as in Fig. 1, is swept; (ii) the phase-sensitive detection displays the lineshape in derivative mode. The chemical structures of TEMPOL (molecular size r_TEMPOL ≈ 0.34 nm) and water (r_H2O ≈ 0.14 nm) molecules are sketched. The unpaired electron of TEMPOL (drawn as a dot) is localized in the NO bond. The theoretical predictions considering the reorientation of TEMPOL with (140 K, 160 K) and without dynamical heterogeneity are also shown.