Reactions of the Dihydroxylamine (HNO₂-•) and Hydronitrite (NO₂2-•) Radical Ions

The dihydroxylamine radical anion (HNO 2 -•, with the H atom on the nitrogen atom) is produced by the reaction of H atoms in the pulse radiolysis of nitrite solutions and decays in water with a rate constant of 5.0 × 10 3 s -1 . Its absorption spectrum has a maximum at 270 nm with molar absorptivity of 2.8 × 10 3 M -1 cm -1 . The decay of HNO 2 -• is catalyzed by both acids and bases. The hydronitrite radical (NO 2 2-• ) produced by the reaction of e aq - with nitrite exhibits no absorption spectrum between 270 and 550 nm. It is much shorter-lived than HNO 2 -•, disappearing at 1.6 × 10 6 s -1 without generating any HNO 2 -• . Neither radical species has any observable p K a 's, but the p K a for HNO 2 -• has been estimated to be lower than 9.3 from the rate data on the hydroxide-catalyzed decomposition of this radical. Both HNO 2 -• and NO 2 2-• reduce methyl viologen, and the reduction by HNO 2 -• has been used to measure its yield, which is found to be 0.63 radicals per 100 eV. Thus, the production of HNO 2 -• by H atoms is quantitative. Collectively, these data represent a major revision of the reductive radiation chemistry of nitrite.