The reactions of the OH radical with H2S and SH⊖ are very fast (k = 1.1·1010 and 5.4·109 mole-1 liter sec-1, respectively). The hydrated electron reacts with H2S (1.1·1010) but does not react with SH⊖. The rate constant of the reaction CNS+SH⊖ CNS⊖ +SH was found to be equal to 9.8·108. Species absorbing at 3800 Å (e ∼ 104 mole-1 liter cm-1) are formed in these reactions of H2S and SH⊖ The intensity of this absorption is very low in strongly acid solutions, increases with pH, goes through a broad maximum at about pH=7, reaches a lower plateau between pH = 8.5 -10.5 and decreases in strongly alkaline solutions. At pH values below 7, the intensity is dependent on the concentrations of both SH⊖ and free H2S, i. e. at constant SH⊖ concentration a stronger absorption occurs if more free H2S is present. In the plateau below pH = 8.5 -10.5, the intensity is practically independent of the SH⊖ concentration above 4·10-5 mole/l. The decay of the 3800 A absorption after the pulse is first order with τ1/2 = 5 μsec independent of the OH⊖ and SH⊖ concentrations in alkaline solutions.Below pH = 7, the absorption disappears by second order, the rate constant being larger at lower pH values. SH or S⊖ absorb weakly in the near UV and do not contribute to the 3800 Å absorption. This absorption is attributed to the ions H2S2⊖ or H2S2⊖ in alkali and to H2S2⊖or higher complexes such as H3S4⊖ in acid. The first order decay of 5 μsec is attributed to the spontaneous decomposition of S2H2⊖ into S⊖ +SH⊖. Two S⊖ ions form S22⊖ (2 k=2·109 mole-1 liter sec-1). The complex H2S2⊖ is formed in the fast reaction SH + SH⊖ ↔ S2H2⊖ (dissociation constant about 4·10-5 mole/l). The formation of an intermediate complex SHOH⊖ in the reaction of OH with SH⊖ is discussed. This intermediate reacts with either SH⊖ to form S2H2⊖ or with OH⊖ (or other proton acceptors such as ΗΡΟ42Θ) to form SΘ+ H2O+OHΘ.

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The following absolute rate constants of the reactions of eaq⊖ and OH with dimethylthioether and dimethylsulfoxide have been determined: k (eaq⊖ + CH3SCH3) =2.0·107 mol-1 l sec-1; k(e⊖+ CH3SOCH3) =1.7·106; k(OH+CH3SCH3) =5.2·109; k(OH+CH3SOCH3) =4.2·109. The acid and basic components of the equilibriumare formed in the reactions of OH+CH3SCH3 and eaq⊖ +CH3SOCH3, respectively. The anion absorbs at 3500 Å. The ρK value of the equilibrium was found to be equal to 10.2. The CH2SCH3 radical (2900 Å) and the ions CH3SCH3⊕ or (CH3SCH3)2⊕ (4700 Å) are also formed in the reaction between OH and CH3SCH3. High thioether and low OH⊖ concentrations favour the formation of the positive ion which is believed to result from a reaction between CH3SOHCH3 and CH3SCH3.

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