Frequency dependence of electron spin relaxation times in aqueous solution for a nitronyl nitroxide radical and perdeuterated-tempone between 250Â MHz and 34Â GHz

► Tumbling correlation times in H2O are 9 ps for 1 and 25 ps for 2. ► For 1 and 2 in H2O T1 ∼ T2 at resonance frequencies below 3 GHz. ► The frequency dependence of 1/T1 was modeled with spin rotation, modulation of anisotropy, and a thermally activated process.