Electron Spin Relaxation of SO2− and SO3− Radicals in Solid Na2S2O4, Na2S2O5, and K2S2O5

Electron spin relaxation times are reported for the SO2− radical in solid Na2S2O4 and K2S2O5, and the SO3− radicals in Na2S2O5, and K2S2O5. Echo envelope modulation was observed for the radicals in the Na+ salts and characterized by HYSCORE. Tm and T1 were measured using spin echo methods from 40 to 293 K and by long-pulse saturation recovery at 293 K. At low temperature Tm for the radicals in K2S2O5 ( 14 μs) is longer than for the radicals in Na2S2O5 (Tm 7 μs) or Na2S2O4 (Tm 4 μs), which is attributed to the low magnetic moment of K+. The shorter value of Tm in Na2S2O4 is attributed in part to higher spin concentration. Tm decreases with increasing temperature as T1 approaches Tm. In each lattice there is a distribution of spin lattice relaxation times that may be due to distributions in interspin distances. The long components in the T1 distributions are longer for SO3− than for SO2−. In 0.5 M NaOH solution at 293 K SO2− has a relaxation-determined Lorentzian peak-to-peak linewidth of about 0.7 G, and T1 T2 100 ns.