Thin-film water ice samples are doped with reactive species, such as OH and HO2 and both singlet and triplet O atoms, which are produced in a discharge, in order to trace the reactions that form oxidants such as H2O2 and O-2, in relation to the icy surfaces of satellites in the outer solar system. The present experiments show that, while reactions of OH formed in the discharge produce H2O2, the majority of H2O2 is formed via other pathways, with reactions of singlet O atoms being the most likely candidate. Strong evidence comes from thermal processing of the ices and using the matrixisolation technique to quantify the OH abundance in the discharge, which is far below the required amount to account for the relatively high H2O2 abundances measured. Reactions of HO2 are also of possible significance but appear to be less dominant in the formation of H2O2 than singlet O.