Pulse radiolysis and transient absorption spectra of aqueous solutions of sodium sulfamate

Chemical kinetics for the reactions of sulfamate ions (NH₂SO₃⁻) with the primary products of water and nitric acid radiolysis were measured in aqueous solutions at ambient temperature. Using time-resolved electron pulse radiolysis techniques with a custom multichannel detection system, we examined the reactivity of NH₂SO₃⁻ with the hydroxyl radical (^•OH), hydrogen atom (H^•), and nitrate radical (NO₃^•). The sulfamate ion was found to react with ^•OH and H^• with second-order rate coefficients of k _•^OH = (5.60 ± 0.04) × 10⁶ M⁻¹ s⁻¹ and k _H^• = (7.96 ± 0.10) × 10⁶ M⁻¹ s⁻¹, respectively, and with NO₃^• with a rate coefficient of k _NO3^• = (1.67 ± 0.06) × 10⁷ M⁻¹ s⁻¹. The reactions of NH₂SO₃⁻ with ^•OH and H^• resulted in the formation of two transient radical species, one with maximum absorbance at 300 nm and a second with maxima at both 300 nm and 600 nm. These spectra are tentatively assigned to ^•NH₂SO₃ and ^•NHSO₃⁻, respectively. By measuring the absorbance of these radicals as a function of pH, the radical p K _a was determined to be 9.5 ± 0.1. Overall, this work has implications for the longevity and performance of ferrous sulfamate, Fe(NH₂SO₃)₂, as a plutonium reductant in the reprocessing of used nuclear fuel.