Spectroscopic capabilities of the time-resolved magnetic field effect technique as illustrated in the study of hexamethylethane radical cation in liquid hexane

Abstract

The method of the time-resolved magnetic field effect in the recombination fluorescence of spin-correlated radical ion pairs can provide information on the parameters of the EPR spectra of short-lived radical ions. The present paper demonstrates these spectroscopic potentialities using, as an example, hexamethylethane radical cation whose EPR spectrum in solution is determined by isotropic hfc with 18 equivalent protons. The hfc constant is determined from the position of peaks of the time-resolved magnetic field effect of the hexamethylethane and perdeuterated p-terphenyl solution in n-hexane at ambient temperature. The difference in the g-values of (hexamethylethane)˙⁺ and (p-terphenyl-d₁₄)˙⁻ radical ions is found by analyzing the curve shape of magnetic field effect for various magnetic field strength. Both the hfc constant and the difference in the g-values coincide with the data obtained by the OD EPR method. Independence of the curve shape on hexamethylethane concentration testifies to the low rate of ion-molecular charge transfer. The method of time resolved magnetic field effect is used to determine the times of longitudinal and transverse paramagnetic relaxation. The dependency of the relaxation rates on magnetic field strength is derived and feasible relaxation mechanisms are discussed.