Radiolytic Reactions of Monochloramine in Aqueous Solutions

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Molecules, spectroscopy, kinetics, environment, & general theory, 2003-09, Vol.107 (38), p.7423-7428
• Main Authors: Poskrebyshev, G. A, Huie, R. E, Neta, P
• Format: Article
• Language: English
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp030198k

Monochloramine reacts with hydrated electrons very rapidly, k(NH2Cl+eaq -) = (2.2 ± 0.3) × 1010 L mol-1 s-1, to produce •NH2 radicals. It reacts with •OH radicals more slowly, k(NH2Cl+•OH) = (5.2 ± 0.6) × 108 L mol-1 s-1, to produce •NHCl radicals. While •NH2 exhibits an absorption peak at 530 nm, with a molar absorption coefficient ε530 = 80 L mol-1 cm-1, •NHCl exhibits two peaks at 330 and 580 nm, ε330 = (85 ± 30) L mol-1 cm-1 and ε580 = (56 ± 30) L mol-1 cm-1. The •NHCl radical undergoes self-decay and can react also with O2 to form a peroxyl radical. It is suggested that the peroxyl radical exists in equilibrium NHClO2 • ⇆ •NHCl + O2 with an estimated equilibrium constant of (3 ± 2) × 10-3 mol L-1. The reaction of chloramine with the carbonate radical is suggested to form a complex [CO3NH2Cl]•- with k f = 2.5 × 105 L mol-1 s-1 and k r = 4 × 102 s-1, and this complex decomposes with k = 7 × 102 s-1 to form •NHCl.