Reactions of the hydroperoxyl radical (HO2) with nitrogen dioxide and tetranitromethane in aqueous solution

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Abstract
HO2 produced in a flow system by the electron beam irradiation of aerated formic acid solutions reacts with tetranitromethane (TNM) in acid solution in two stages. Rapid formation of nitroform by reaction (1) is followed by a delayed reaction with 0.5 s < t½ < 10 min. The delayed reaction forms nearly half the total nitroform at low [TNM] and pH; it is suppressed by KCNS and is believed to be due to reduction of TNM by peroxynitric acid (HO2NO2) formed in the mechanism: HO2⇌ O– 2+ H+, C(NO2)4+– 2→ C(NO2)– 3+ O2+ NO2, k1= 2 × 109 dm3 mol–1 s–1(1), HO2+NO2→ HO2NO2k10= 4 × 109 dm3 mol–1 s–1(10), 2NO2→ N2O4, k13= 1010 dm3 mol–1 s–1(13), N2O4+ H2O → HNO2+ HNO3. Quantitative evidence for this mechanism is presented.