Effect of Pressure on the Rates of Reaction of Solvated Electrons in Liquid Ethanol

Abstract

At a γ radiolysis dose of ${\text{1× 10}}^{18}\hspace{0.17em}\mathrm{eV/g}$ in ethanol at 296°K the hydrogen yields in neutral ethanol were $\mathrm{G(}{\mathrm{H}}_2\text{)=5.0}$ at 1 bar and 5.5 at 5.3 kbar; in 1 mM and 1 M sulfuric acid $\mathrm{G(}{\mathrm{H}}_2\text{)=5.7}$ , independent of pressure. The electron scavengers nitrobenzene, acetone, and naphthalene reduce the hydrogen yields in neutral and acidic ethanol at 1 bar and 5.3 kbar; increasing the pressure greatly reduces the ease of scavenging the free ions but has only a small effect on scavenging efficiency in the spurs. Using as a standard the reaction $e_{\mathrm{solv}}^{-}\to {\mathrm{C}}_2{\mathrm{H}}_5{\mathrm{O}}_{\mathrm{solv}}^{-}+\mathrm{H}$ with ${\text{k=1.2× 10}}^5\hspace{0.17em}{\sec }^{\text{−1}}$ at 1 bar and $\text{Δ V‡ =−14.4\hspace{0.17em}}{\mathrm{cm}}^2/\mathrm{mole}$ averaged between 0 and 5.3 kbar, one obtains the following values for ${\mathrm{k(M}}^{\text{−1}}·{\sec }^{\text{−1}})$ and $\mathrm{\Delta \; V‡\hspace{0.17em}(}{\mathrm{cm}}^3/\mathrm{mole}{\mathrm{):\; e}}_{\mathrm{solv}}^{-}+{\mathrm{H}}_{\mathrm{solv}}^{+}$ , ${\text{2.8× 10}}^{10}$ at zero ionic strength, +4.5; $e_{\mathrm{solv}}^{-}+{\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NO}}_2{\text{,\hspace{0.17em}1.5× 10}}^{10}{\text{,\hspace{0.17em}+7.5;\hspace{0.17em}e}}_{\mathrm{solv}}^{-}+\mathrm{naphthalene}{\text{,\hspace{0.17em}5.0× 10}}^9{\text{,\hspace{0.17em}+5.6;\hspace{0.17em}e}}_{\mathrm{solv}}^{-}+{\mathrm{CH}}_3{\mathrm{COCH}}_3{\text{,\hspace{0.17em}4.2× 10}}^9\text{,\hspace{0.17em}+5.1}$ . The diffusion coefficient of solvated electrons in ethanol appears to correlate with the liquid viscosity; this is different from the behavior of electrons in alkanes. In ethanol ${\mathrm{\Delta \; V‡}}_{\mathrm{diffusion}}\text{≈ +7\hspace{0.17em}}{\mathrm{cm}}^3/\mathrm{mole}$ for $e_{\mathrm{solv}}^{-}\hspace{0.17em}\mathrm{and}\text{\hspace{0.17em}+4\hspace{0.17em}}{\mathrm{cm}}^3/\mathrm{mole}$ for ${\mathrm{H}}_{\mathrm{solv}}^{+}$ . The free ion yield in ethanol is ${\mathrm{G(e}}_{\mathrm{solv}}^{-}{)}_{\mathrm{fi}}\text{=1.7}$ , independent of pressure from 1 bar to 5.3 kbar; the model of Freeman and Fayadh [J. Chem. Phys. 43, 86 (1965)] is consistent with this behavior and it predicts that G_fi in methanol and water are also independent of pressure.