γ Radiolysis of Liquids at High Pressures. III. Aqueous Solutions of Sodium Bicarbonate

Abstract

The γ radiolysis of deaerated aqueous solutions containing sodium bicarbonate and either glucose or isopropanol has been studied at ∼20° in the applied pressure range 0 to 7 kbar. For 0.05M bicarbonate and 0.036M isopropanol, G(H₂) increases from 0.89 to 2.43 as applied pressure increases from 0 to 6.9 kbar. A 100‐fold change (0.005–0.5M) in bicarbonate concentration has little or no effect on the pressure dependence of G(H₂). Because primary yields are invariant over the pressure range studied, the results are interpreted in terms of an effect of pressure on the competition between Reactions [2] and [3] $$e_{\mathrm{aq}}^{-}+{\mathrm{CO}}_2\to {\mathrm{CO}}_2^{-},$$ $$e_{\mathrm{aq}}^{-}+{\mathrm{HCO}}_3^{-}\to \mathrm{H}+{\mathrm{CO}}_3^{\text{2−}},$$ with Reaction [3] followed by Reaction [4] $$\mathrm{H}+\mathrm{RH}\to \mathrm{R}+{\mathrm{H}}_2.$$ Such an interpretation gives a difference in activation volumes of Reactions [2] and [3] as ΔV₂^‡—ΔV₃^‡≈18.4 ml mole⁻¹ and a specific rate k₃⁰≈6×10⁵M⁻¹· sec⁻¹ at atmospheric pressure. Assumption that Reaction [2] is diffusion controlled permits estimation of ΔV₂^‡≈1.6 ml mole⁻¹, from the pressure dependence of water viscosity. Thus, ΔV₃^‡≈−16.8 ml mole⁻¹. The latter value, in turn, yields an estimate of V̄(e_aq⁻) in the range −10.9 to −6.5 ml mole⁻¹ relative to V̄(H⁺)=0. Use of an absolute value of V̄₀(H⁺)=−5.4 ml mole⁻¹ gives an absolute value of V̄₀(e_aq⁻) in the range −5.5 to −1.1 ml mole⁻¹. Approximate equality of the values for V̄₀ of the electron and of the proton is consistent with their having a negligible intrinsic volume and approximately equal electrostriction volumes.