The pulse radiolysis of aqueous tetranitromethane. I. Rate constants and the extinction coefficient of e_aq^-· II. Oxygenated solutions

Aqueous solutions of tetranitromethane (TNM), both deaerated and oxygenated, have been investigated by the technique of pulsed radiolysis. This system enabled the direct determination of ∈_e⁵⁷⁸⁰, the extinction coefficient of the hydrated electron, at 5780 Å. as 10,600 (±10%) M^-1 cm.^-1. ∈_e⁵⁷⁸⁰ is essential for evaluating rate constants previously determined as k/∈_e⁵⁷⁸⁰. Also from ∈_e⁵⁷⁸⁰ we calculate G_e = 2.6 from values of G_e × ∈_e⁵⁷⁸⁰ in the literature. A number of rate constants were determined, including k(e_aq^- + TNM) = 4.6 × 10¹⁰ M^-1 sec.^-1, k(H + TNM) = 5.5 × 10⁸ M^-1 sec.^-1, and k(e_aq^- + NF^-) = 3.0 × 10¹⁰ M^-1 sec.^-1, where NF^- is the nitroform ion. Rate constants have also been measured for reaction of several organic radicals with TNM. In the presence of O₂, k(O₂^- + TNM) was measured as 1.9 × 10⁹ M^-1 sec.^-1. k(HO₂ + TNM) is less than 10^-5 as large. Measurement of the effective k as a function of pH gave pK = 4.45 ± 0.25 for the dissociation, HO₂ ⇌ H⁺ + O₂^-.