MECHANISM OF HYDROGEN FORMATION IN GAMMA RADIOLYSIS OF 1,4-DIOXANE AND ITS MIXTURES WITH WATER

In the γ irradiation of pure liquid 1,4-dioxane, G(H2) = 1.31 was obtained. The hydrogen yield is suppressed to a limit of G(H2) ≈ 1.0 by the H atom scavenger 1-hexene and by the electron scavengers N2O and C-C4F8. Consequently, G(H2) ≈ 1.0 is attributed to molecular elimination from directly excited dioxane molecules. The yield of scavengeable electrons, as determined with N2O and 0.1 N H2SO4, corresponds to G = 3.1-3.4. Thus G(H2) ≈ 0.3 results from H atoms produced with ∼10% efficiency in the neutralization of dioxane cations by electrons. An enhancement of G(H2) by NH3 is observed that indicates proton transfer from a dioxane cation to give NH4+, which on neutralization by an electron presumably yields H with unit efficiency Water is considerably less effective than NH3 in the enhancement of G(H2); the results suggest that the specific rate of proton transfer to H2O is less than that to NH3 in liquid dioxane. As the water-dioxane composition is varied over the whole range, G(H2) passes through a maximum. Such behavior is related to a change in the yield of free solvated electrons with change in the dielectric constant of the medium. The presence of dioxane in cyclohexane causes a suppression of G(H2), which is restored by the addition of methanol or NH3. The results indicate that positive charge is transferred from cyclohexane cations to dioxane and that the added base scavenges cations of both cyelohexane and dioxane with about equal efficiency.