Water radiolysis molecular yields

The superoxide radical (HOj/Oj") is a peculiar case in water radiolysis. Its yield of production increases with LET which is completely contrary to the recombination rule in dense ionization tracks. Actually, the general trend is that these radical recombinations increase the production of molecular species (H2 and H2O2). The low reactivity of this radical in pure water essentially due to its... 

Samuel and Magee (1953) employed a 1-radical model to find the relative forward yield in water radiolysis as a function of radiation quality. In such models, no distinction is made between reactive radicals or molecular products. The products of radiolysis are called forward (F) to denote observable molecular yield or radical (R), denoting yield of scavenger reaction at small concentration. The aim of the theory is to calculate the relative forward yield G(F)/[G(F) + G(R)], where the G values refer to the respective yields for 100 eV energy absorbed in... 

In the early days of water radiolysis, it was empirically established in several instances that the reduction of molecular yield by a scavenger was proportional to the cube root of its concentration (Mahlman and Sworski, 1967). Despite attempts by the Russian school to derive the so-called cube root law from the diffusion model (Byakov, 1963 Nichiporov and Byakov, 1975), more rigorous treatments failed to obtain that (Kuppermann, 1961 Mozumder, 1977). In fact, it has been shown that in the limit of small concentration, the reduction of molecular yield by a scavenger should be given by a square root law in the orthodox... 

The question of the amount of the initial yield of water decomposition or of the initial yields of H and OH radicals is of interest. These yields include the yield of those radicals that take part in alpha-particle tracks in recombination reactions (H -f- H, OH -f- OH), in a track region in reactions of radiolysis molecular product decomposition (H202 + OH, H202 + H, Ho -f- OH), and in a solution volume—in reactions with solutes. Only the recombination reaction H + OH was not taken into account. 

Average values calculated of some radical and molecular yields in the radiolysis of water by 2 rays of Co(It is actually more difficult to give sure values for OC - rays). 

The radiolysis of water produces hydrated electrons (e q, G = 2.9), hydrogen atoms (G = 0.55) and hydroxyl radicals (G = 2.8) which react with the solute molecules. In addition, the radiolysis of aqueous solutions also yields H202 (G = 0.75), gaseous hydrogen (G = 0.45) and hydronium ions (H30+, G = 2.9). In most cases the molecular products do not interfere with the reactions of the radicals. To study the reaction of one radical with the solute without interference from other radicals, scavengers for the other radicals should be added7-10. 

Radiolysis of oxygenated water or photolysis of hydrogen peroxide solutions yields two oxidative species, the -OH radical and the perhy-droxyl radical (HO2 02" + H ). As previously discussed, the final reaction product of hydroxyl radicals interaction with ascorbate above pH 6 is predominantly the ascorbate anion radical (A ). To account for the stoichiometry of ascorbic acid consumption in a Co gamma ray study of oxygenated ascorbic acid solutions, the ascorbic acid free radical was thought (3) to react with molecular oxygen to yield a transient adduct ... 

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