Primary Radical Yields in Pulse-Irradiated Alkaline Aqueous Solution

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Abstract
Relative primary radical yields of hydrated electrons, H atoms, and OH radicals were determined by measuring the amount of hydrated electron formed following a single 4-usec. pulse of X-rays. In neutral solution the amount of hydrated electron produced corresponds to G(eaq), and at high pH''s an additional amount is formed corresponding to G(H) by the reaction H + OH- =H2O + eaq- In the presence of dissolved H2 the OH radical in yield G(OH) is also converted to hydrated electrons by reaction with H2. The high optical absorption of the hydrated electron at 7000 A is used as a measure of its concentration. A pH range from 7 to 14. 5 is covered. At pH above 12 the total radical yield, G(eaq) + G(H) + G(OH), is constant, as is the total reducing yield, G(eaq) + G(H). These relative yields are placed on an absolute basis by measuring the manganate ion yield in a formate-permanganate solution. The value of G(eaq) is 2.7 in neutral and 3.1 in strong alkaline solutions. The primary radical yields g(eaq), g(H), and g(OH), computed from diffusion theory, are 3. 04, 0. 53, and 2. 81 at pH 13, respectively, and g(eaq) =2. 65 at pH 7. The mechanism of the pH effect is briefly discussed.

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