The radical scavenging technique with product analysis was employed to determine quantum yields for the two main processes (1) N03~+ hv = N02" + O and (2) N03~+ H+ + hv = N02 + OH in dilute, air-saturated solutions of sodium nitrate. Oxygen atoms were detected by their reaction with cyclopentene and the production of ethene. The quantum yield found was ( ) = (1.1 ±0.1) x 10~3. The generation of OH radicals was confirmed by their reactions with benzene to give phenol and with 2-propanol to produce acetone. The second reaction was used to establish an OH quantum yield of ( ) = (9.2 ± 0.4) X 10~3 5. Nitrite was formed with a similar yield in the pH region 5-12, whereas at lower pH the yield declined. Formate as a scavenger converts OH radicals toward 02~/H02 radicals which produce H202. The yield of H202 at pH 5.6 was lower than expected whereas that of NOf was higher. Reactions are postulated to explain this observation as well as the pH dependence of nitrite formation.
Nitrate ion photodecomposition is explored as a source of OH radicals for the determination of rate coefficients associated with OH reactions in aerated aqueous solutions. The oxidation of benzene to phenol serves as a standard reaction phenol provides an indicator for the extent of competition by other reactants. Rate coefficients for ten organic compounds, determined relative to that for benzene, are in good agreement with literature values over a range of 3 orders of magnitude. By comparison with the yield of acetone from the reaction of OH with 2‐propanol the yield of phenol from the reaction with benzene is found to be ∼0.95. The reaction of OH with hydroxymethane sulfonate generates sulfate as a major product. It was not possible to determine the associated rate coefficient with the competition technique because the data for sulfate and phenol show the reaction to be a chain process in which SO−4 radicals appear to be the main chain carrier. Steady state calculations based on a postulated reaction mechanism indicate for the reaction OH + HMS a rate coefficient exceeding 1 · 109 M−1 s−1.
Using the radical scavenging technique with product analysis the quantum yields for the two main reaction channels (see scheme) of the photodecomposition of NO3‐ in dilute, air‐saturated solutions of NaNO3 are determined.
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