Linewidth alternation in the e.s.r. spectrum of the 1,4-benzosemiquinone free radical anion in ether solution

Abstract

The e.s.r. spectra of potassium, rubidium and caesium 1,4-benzosemiquinone in D.M.E. have been recorded from –80°C to room temperature. In all cases, marked line width alternation has been found and, from the behaviour of the caesium hyperfine splittings, the process responsible for the line broadening is one in which the spin state of the alkali metal is preserved. The observations suggest two-site cation oscillation as the line broadening process and all the features expected from the theory for this have been found for the three alkali metal semiquinone ion-pairs. As the temperature is lowered the degree of ionization of all the three ion-pairs increases. In the temperature range from –60 to –80°C the spectrum of an additional species has been found for each of the alkali metal semiquinones. Possible explanations of this have been discussed.