Optical detection of ESR spectra of short-lived ion-radical pairs produced in solution by ionizing radiation

A new and very sensitive technique to detect ESR spectra of short-lived radical pairs in solution is proposed on the basis of optical detection of magnetic resonance (ODMR). An ODMR spectrometer has been constructed for detecting ESR spectra of ion-radical pairs created by ionizing radiation. The singlet ESR signal from (naphthalene)-/(naphthalene)+ pairs has been observed in a naphthalene solution in squalene at an average concentration of 20 radical pairs per sample with a signal-to-noise ratio equal to 10/1. The hyperfine structure has been resolved in the ESR spectrum of (diphenyl)-/(diphenyl)+ pairs at a low diphenyl concentration in squalane and spectrum narrowing due to charge-transfer reaction has been observed at a high diphenyl concentration