Silent Discharge Reactions in Aqueous Solutions. I. An Acidic Aqueous Solution of Ferrous Sulfate in Atmospheres of Helium and Argon

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Abstract
In an atmosphere of helium or argon, the silent discharge reactions of aqueous solutions have been investigated from the point of view of radiation chemistry. A discharge tube with two coaxial glass tubes was used. In a dilute oxygen-free aqueous solution of sulfuric acid, hydrogen peroxide appeared as a result of discharge. Also, the oxidation of ferrous ions to ferric ions has been found. It has been confirmed, first, that neither the effect of metastable excited states of helium and argon nor that of luminescence is serious, and, second, that the reaction may well be interpreted by taking into consideration the actions of slow electrons generated in the gas phase on the liquid water. The yield of hydrogen atoms plus hydroxyl radicals has been estimated from the yields of hydrogen peroxide and ferric ions. The ratios of the yield of hydrogen peroxide to that of radicals show that the silent discharge reaction corresponds to the reaction by ionizing radiation of high LET, the value of which apparently equals 3eV./Å in helium and 8 eV./Å in argon. The G(Fe3+) value and the absorbed dose (E) estimated were, respectively, as follows: In helium: G(Fe3+)=4.6, E=3.8×106 r./hr.; in argon: G(Fe3+)=4.3, E=7.2×106 r./hr.