Sign of the 17O Hyperfine Coupling Constant in Fremy's Salt

The electron spin resonance spectrum of Fremy's salt—17O, [(SO3)2N17O]K2—has been studied in aqueous solution. Twelve out of the expected 18 17O satellites were clearly resolved. The measured hyperfine coupling constant for 17O, aO, is 20.7±0.2 G. Variations in linewidth between the 17O satellites were observed and interpreted quantitatively in terms of relaxation by modulation of the anisotropic dipolar and g tensors. The relaxation rate is mainly determined by interactions involving the magnetic moment of 17O. The terms in the expression for the linewidth that depend on mN are small, except for a cross term EmNmO. Analysis of the results combined with a knowledge of the sign of the g-tensor anisotropy allowed the determination of the signs of aN and aO, which are positive and negative, respectively.