Thin-film water ice samples are doped with reactive species, such as OH and HO(2) and both singlet and triplet O atoms, which are produced in a discharge, in order to trace the reactions that form oxidants such as H(2)O(2) 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 H(2)O(2), the majority of H(2)O(2) 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 matrix-isolation technique to quantify the OH abundance in the discharge, which is far below the required amount to account for the relatively high H(2)O(2) abundances measured. Reactions of HO(2) are also of possible significance but appear to be less dominant in the formation of H(2)O(2) than singlet O.