2H₂O radiation 2H₂ O₂ H₂O H₂O H₃O OH e_aq H₃O H H₂O e_aq H₂O H OH EFFECTS OF RADIATION DOE-HDBK-1015/2-93 Reactor Water Chemistry ON WATER CHEMISTRY (SYNTHESIS) CH-03 Rev. 0 Page 2 Both of these species are very reactive chemically, and there are several reaction pathways available to each.  Some of these mechanisms are very complex and are usually of little practical value to the reactor operator, who is more concerned with the overall, observable effects.  In the case of water, the overall effect of irradiation is shown in the following reaction. (3-2) Because this result is not at all apparent from Reaction (3-1), the following section describes the intermediate processes in some detail.  This discussion is presented only to illustrate the types  of  reaction  mechanisms  that  occur  in  irradiated  solutions.    Subsequent  discussions primarily involve only the overall effects of these processes. Reaction (3-1) shows that irradiation of pure water produces an electron and a H  O   ion.  As 2 + stated, both species are highly reactive.  The H  O   ion rapidly reacts with a water molecule as 2 + follows. (3-3) The species OH is an uncharged hydroxyl group.  Neutral groups such as this, in which all chemical  bonding  capacity  is  not  satisfied,  are  common  intermediate  species  in  chemical reactions and are called radicals or sometimes free radicals. The electron produced by Reaction (3-1) first forms a species called the hydrated electron, denoted by e .  The hydrated electron may be thought of as resulting from the interaction of aq - a negative electron with the positive end of a polar water molecule.  This is analogous to the formation of hydronium ions by interaction of a positive proton (H  ) with the negative end of + a water molecule.  Because the water molecules associated with hydrated electrons do not participate in subsequent chemical reactions, they are not shown in chemical equations, and the hydrated electron (e ) is used instead. aq - Hydrated electrons may interact with H  O   ions in solution or with water molecules.  Both 3 + reactions produce another reactive species, atomic hydrogen. (3-4) or (3-5) Reaction (3-4) usually predominates.