MARY-detected ESR spectra of radical ions in liquid solutions for systems with crossing Zeeman levels

The effect of Zeeman levels crossing in spin-correlated radical ion pairs (naphthalene)+/(hexafluorobenzene)− was monitored as the influence of an external magnetic field on the solution fluorescence under X-irradiation (MARY spectrum). The spectra obtained exhibit a line in the field, equal to triple the hfi coupling constant of hexafluorobenzene radical anion, its linewidth being determined by the unresolved hyperfine structure of the naphthalene cation. The theory predicts that the presence of weak hfi in the partner cation splits this line by the projections of the cation total nuclear momentum MZ according to nuclear statistics. Thus, a direct correspondence between the MARY and ESR spectra of radical cations allows registration of the ESR spectrum without microwave pumping.