Zero-Field Electron Magnetic Resonance in Some Inorganic and Organic Radicals

Abstract

Zero-field electron magnetic resonance (EMR) spectra have been observed for several dilute paramagnetic systems. Among these are peroxylamine disulfonate ions in aqueous solutions, Cr3+ in single crystals of MgO, free radicals in x-irradiated powders of malonic acid, potassium hydrogen malonate, dipotassium malonate, succinic acid, and glutaconic acid. Zero-field spectra were observed by means of a marginal oscillator—detector similar to that of Benedek and Kushida. The zero-field splittings in the systems studied were due exclusively to the hyperfine couplings between electronic and nuclear spins. Results obtained were in good agreement with high-field EMR measurements on these systems. In several cases the hyperfine couplings were obtained with greater precision than at high field. In addition, the radical —OOC–ĊH–COO— was identified, for the first time, in irradiated dipotassium malonate by means of its zero-field spectrum. No zero-field lines could be detected in electron-irradiated polyethylene. Advantages and disadvantages of the zero-field technique are discussed.