Photolytic and radiolytic oxidation of humic acid.

The reactions of Br(2)(˙-), Br˙, HO˙ and N(3)˙ with Aldrich humic acid (AHA) were investigated. The Br/Br(2)(˙-) radicals were obtained in flash-photolysis experiments (λ(exc) = 266 nm) performed with NaS(2)O(8) solutions in the presence of bromide ions. HO˙ and N(3)˙ radicals were generated by pulse radiolysis of N(2)O-saturated solutions. From the combination of a bilinear analysis and computer simulations of the absorbance traces, it was possible to obtain information on the rate constants for the reactions of Br(2)(˙-), Br˙, HO˙ and N(3)˙ with AHA and on the intermediate species involved in the mechanism. Evidence for the participation of phenoxyl radicals (λ(max) = 410 nm) is given.