The radiation chemical redox transformations in solutions of bromides in the presence of minor additives of iodides were studied by pulse radiolysis. The change in the concentrations of the Br -and I -ions changes the ratio of the formed short lived radical anions Br 2 •-, BrI •-, and I 2 •-. The spectrum of the mixed radical anion BrI •-contains a broad optical band at 370 nm with ε 370 = 9650 L mol -1 cm -1 . The reduction potential of the BrI •-/Br -, I -pair is 1.25 V. The rate constants for the forward and backward reactions Br 2•-+ IBrI •-+ Br -are k f = 4.3•10 9 and k r = 1.0•10 5 L mol -1 s -1 , respectively; for the reactions BrI •-Br -+ I • , k f = 5.7•10 8 s -1 and k r = 1.0•10 10 L mol -1 s -1 .The reactions of one electron oxidation of the Cl -, Br -, and I -ions that occur upon the radiolysis or photolysis of aqueous solutions of halides afford intermediate short lived radical anions Cl 2 •-, Br 2 •-, and I 2 •-(see review 1 ). They exhibit properties of strong oxidants. The rate constants for many one electron oxidation reactions of organic and inorganic compounds involving these radical anions were measured by pulse radiolysis and photolysis. 2 It was found 3 that Cl 2 •-interacts with the Br -ion to form the mixed radical anion ClBr •-. This species occu pies an intermediate position between the radical anions Cl 2 •-and Br 2 •-in the properties. For instance, the maxi mum of the optical band (λ max ) in the spectrum of this species lies at a wavelength of 350 nm, and the molar absorption coefficient (ε) is 9.3•10 3 L mol -1 cm -1 . 3 The corresponding parameters for Cl 2 •-are 340 nm and 8.8•10 3 L mol -1 cm -1 , 4 and for Br 2 •-they are 360 nm and 9.9•10 3 L mol -1 cm -1 . 5 The standard redox poten tials of the Cl 2 •-/2Cl -and Br 2 •-/2Br -pairs are 2.09 and 1.66 V. 6 The calculated E 0 potential for the ClBr •-/Cl -,Brpair is 1.85 V. 3 The radical anions Cl 2 •-interact with the I -ion in a different manner. 7 In this case, no mixed radi cal anion is formed, but the I • atoms, which are further transformed into the radical anions I 2 •-, are generated. In authors´ opinion, 7 this difference in the mechanism of oxidation of the Br -and I -ions with the radical anions Cl 2•-is a consequence of the difference between the values E 0 (Cl 2 •-/2Cl -) = 2.09 V and E 0 (Br • /Br -) = 1.93 V, as well as E 0 (I • /I -) = 1.33 V. In the first case, the potential difference is only 0.16 V, which is favorable for the organi zation of a mixed orbital in ClBr •-. In the second case, the difference reaches 0.76 V, and the transfer of an electron from I -to Cl 2 •-turns out to be energetically more favorable. A comparison of E 0 (Br 2 •-/2Br -) = 1.66 V with E 0 (I 2 •-/2I -) = 1.03 V and E 0 (I • /I -) = 1.33 V (see Ref. 6) suggests that the radical anions Br 2 •-can oxidize the I -ions. However, this reaction was not studied until pres ently. The potential difference between E 0 (Br 2 •-/2Br -) and E 0 (I • /I -) is 0.33 V, and the formation of the mixed radical anions BrI •-can be expected, as it is obse...
