Observation of spin-correlated radical pairs via two-dimensional electron paramagnetic resonance nutation spectroscopy

Abstract

Two-dimensional (2D) Fourier-transform (FT) electron paramagnetic resonance (EPR) nutation experiments were done in order to verify anomalous flip-angle dependence of a FT–EPR spectrum of a photochemically generated spin-correlated radical pair (SCRP). It was demonstrated by both the experiment and theory that the signals of SCRP have additionally higher and lower nutation frequencies than that of a free radical. This spectroscopy provides a direct spectroscopic evidence of spin-correlation within SCRP, and enables one to partially separate SCRP signals from free radical signals in the 2D EPR spectrum.