Radical scavenging rate constants determined by spin relaxation times of electron spin polarized radicals as measured by free induction decay signals.

This article focuses on a novel method for determining radical scavenging reaction rate constants by monitoring the decay of dynamic electron spin polarization (DEP) through free induction decay (FID) detection using pulsed electron paramagnetic resonance (EPR) spectroscopy. The method was applied to measure rate constants for various organic radicals—including hydroxycyclohexyl, 2-hydroxypropyl, diphenylphosphinoyl, and α,α-dimethoxybenzyl radicals—reacting with different scavengers, and the results showed good agreement with those obtained by the established electron spin echo (ESE) decay method. Compared to the ESE method, the FID approach offers simpler experimental procedures and generally stronger signal intensity but has lower spectral selectivity and requires careful analysis when additional DEP generation occurs. Overall, the study concludes that FID detection is a useful and complementary technique for measuring radical reaction kinetics in photolysis-generated radical systems.