Determination of radicals recombination rate constants

Hydrogen peroxide, in the case of water radiolysis process, is mainly forme d by reaction : (1)OH + OH --> H2O2. A competition exists at alkaline pH be tween (1) and the reactions : (3)OH + O- --> HO2- and (4) O- + O- --> O-2(2 -). The rate constants of the two last reactions are not well known. In ord er to measure more precisely these rate constants, we use an experimental m ethod of competition completed by a simulation of the kinetics. We have det ermined : k((3)) = 10(9) M-1 s(-1) and k((4))= 10(8) M-1 s(-1).