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

Abstract

At a γ radiolysis dose of 1× 1018 eV/g in ethanol at 296°K the hydrogen yields in neutral ethanol were G(H2)=5.0 at 1 bar and 5.5 at 5.3 kbar; in 1 mM and 1 M sulfuric acid G(H2)=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 esolv−→ C2H5Osolv−+H with k=1.2× 105 sec−1 at 1 bar and Δ V‡ =−14.4 cm2/mole averaged between 0 and 5.3 kbar, one obtains the following values for k(M−1· sec−1) and Δ V‡ (cm3/mole): esolv−+Hsolv+, 2.8× 1010 at zero ionic strength, +4.5; esolv−+C6H5NO2, 1.5× 1010, +7.5; esolv−+naphthalene, 5.0× 109, +5.6; esolv−+CH3COCH3, 4.2× 109, +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 Δ V‡diffusion≈ +7 cm3/mole for esolv− and +4 cm3/mole for Hsolv+. The free ion yield in ethanol is G(esolv−)fi=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 Gfi in methanol and water are also independent of pressure.