Radical and molecular yields in the γ -radiolysis of water. II. The potassium iodide-nitrous oxyde system in the pH range 0 to 14

H$_2$, O$_2$, N$_2$, I$_2$ and H$_2$O$_2$ for $^{60}$Co $\gamma$-irradiation of aqueous solutions of potassium iodide containing N$_2$O have been measured at eleven values of pH in the range 0.1 to 14. As the pH is increased G(N$_2$) increases from 0.25 at pH 0.1 to 3.2 at pH 4 remaining constant to pH 10.8 when it again increases to 4 at pH 14. G(I$_2$) decreases from 1 at pH 0.1, passes through a minimum of 0.65 at pH 1.1, then increases to a constant value of 2.3 in the range 4 < pH < 11, thereafter increasing to 3.8 at pH 14. G(H$_2$) falls from 1.1 at pH 0.1 to a constant value of 0.4 at pH $\geqslant$ 2, and G(H$_2$O$_2$)+G(O$_2$) is constant at 0.6 from pH 0 to 10, thereafter declining slowly to 0.34. These and other data which are presented are interpreted on the basis that G$_{e\overline{aq}}$. = 2.3 and G$_H$ = 0.6 over the whole pH range, and that excited water molecules are also formed which can react with N$_2$O ($\rightarrow$ N$_2$ + 2OH), with OH$^- (\rightarrow$ e$^-_{aq}.$ + OH), with H$^+$ ($\rightarrow$ H$^+_2$ + OH) and that O$^-$, OH and H$^+_2$ oxidize iodide ions whereas H reduces I$^-_3$. Thus the available 'conventional' radical yields 'G$_H$' and 'G$_{OH}$' increase with either increasing electron scavenger concentration, e.g. O$_2$ and N$_2$O, or increasing [H$^+$] or [OH$^-$]. Radical and molecular yields for alkaline solutions obtained by other methods are reviewed.