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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.

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Quantum yields of phenol and nitrate, produced by photodecomposition in aqueous solutions of NO2 - and HNO2 in the presence of benzene as scavenger for OH radicals, have been determined as a function of wavelength between 280 and 390 nm. The production of phenol was used to calculate primary OH quantum yields. For NO2 - photolysis at pH 6 Φ1(OH) was found to decrease with increasing wavelength from 0.069 ± 0.008 at 280 nm to 0.022 ± 0.004 at 390 nm, in agreement with previous data. The OH quantum yield Φ2(OH) for the photolysis of HNO2 at pH 2 was essentially constant over the entire wavelength range with Φ2 = 0.35 ± 0.02 (2σ). Quantum yields for NO3 - are comparable in magnitude to those of phenol, indicating that NO as primary product is largely oxidized to nitrate. The most likely conversion processes are reactions of NO with O2 - (pH 6), the latter resulting from the oxidation of benzene, to form peroxynitrous acid, which undergoes thermal decomposition, and of NO2 with HO2 (pH 2) to form peroxynitric acid, which reacts further with HNO2. The rate of NO3 - production decreases with time in the photolysis of NO2 -, whereas it increases in the photolysis of HNO2, and these features remain unexplained.

New data are presented for the quantum yields of CO and H2 produced in the photodecomposition of formaldehyde. The data were obtained at the two temperatures 220 and 300 K, as a function of wavelength in the spectral range 253–353 nm, and as a function of pressure at the wavelengths 339.3 and 353.1 nm. The influence of temperature occurs mainly on the quenching constants describing the pressure dependence. The results are compared with previous data and improved quantum yield curves are presented for applications in atmospheric chemistry.

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A zinc arc lamp and a mercury lamp, respectively, were used to study the photodecomposition of HSO 3 -and SO 3 2-in aqueous solutions saturated with either argon or nitrous oxide. The main products in both cases were sulfate and dithionate, which are attributed to arise from the self-reaction of SO 3 -radicals. Quantum yields for the formation of SO 3 -in argon-saturated solution based on hydrazoic acid and/or ferric oxalate actinometry were 0.19 ( 0.03 for HSO 3 -and 0.39 ( 0.03 for SO 3 2-, essentially independent of S(IV) concentration. In both systems, the rate of sulfate formation rose with time at the expense of that of dithionate. This is explained by reactions of hydrogen atoms and hydrated electrons with dithionate (rate coefficient k 5 ≈ 2 × 10 5 dm 3 mol -1 s -1 ). N 2 O as a scavenger for these radicals removed the effect and raised the quantum yields to 0.25 ( 0.03 and 0.75 ( 0.04, respectively. The product ratios under these conditions were [S 2 O 6 2-]/ [SO 4 2-] ) 0.43 ( 0.04 for HSO 3 -and 0.61 ( 0.03 for SO 3 2-. In oxygen-saturated solutions, the photolysis of HSO 3 -led to a short chain reaction with sulfate and peroxodisulfate as products. The latter product was assigned to arise from the recombination of SO 5 -radicals. Steady state analysis of the product evolution with time gave rate coefficients for two of the reactions involved: k 16 (SO 5 -+ HSO 3 -) ) (1.2 ( 0.4) × 10 4 dm 3 mol -1 s -1 for the main propagation reaction and k 19a (HO 2 + SO 5 -) ) (1.8 ( 1.0) × 10 9 dm 3 mol -1 s -1 for the principal termination reaction. These values agree well with recent data from radiolysis experiments.

Quantum yields for the products CH3CHO, CO2 and CH3COOH in the 350 nm photodecomposition of pyruvic acid are 0.48 ± 0.01, 1.27 ± 0.18 and 0.14, respectively, as measured in air at atmospheric pressure. In the presence of NO2 the quantum yield for CH3CHO was reduced to 0.30 ± 0.04 and peroxyacetyl nitrate was formed with a quantum yield of 0.15 ± 0.02. This is taken to indicate the formation of acetyl radicals in one of the primary processes.