Knud Sehested

Reactions of H2O3 in the Pulse‐Irradiated Fe(II)–O2 System

G[Fe(III)] is measured in pulse‐irradiated O2‐saturated solutions of 20 to 160 μMFe(II), at the pHs 0.46, 1.51, and 2.74 H2SO4 and HClO4 and with dose rates between 1 and 8 krad/1 μsec pulse. Based on homogeneous kinetics, the results are interpreted by a system of 18 reactions. The formation of the hydrogen sesquioxide H2O3 as an intermediate in the reaction OHu2009+u2009HO2→H2O3→H2Ou2009+u2009O2 is confirmed. In the absence of Fe(II), G(H2O3) varies from 2.04 at pH 0.46 to 1.57 at pH 2.74. The rate constant k[H2O3+Fe(II)]u2009=u20096.0u2009×u20091 4M−1·sec−1 at the pHs studied. The direct reaction, OHu2009+u2009HO2u2009=u2009H2Ou2009+u2009O2, does not take place. In H1SO4, at pH 0.46, 151, and 2.74 and in HClO4 at pH 0.46 and 1.51, the complexes of Fe(III) produced by the radiation reach equilibrium before they react with HO2. However, equilibrium is not reached in HClO4 at pH 2.74, where the effective rate constant k(HO2+Fe(III)] is 6.2 times its value when Fe(III) is in its equilibrium form. This ratio is constant over the dose rate range studied. With d...

Pulse radiolysis of methyl viologen in aqueous solutions

Pulse radiolysis of air-free aqueous methyl viologen (MV2+) solutions was carried out at various pH. The attack of e–aq on MV2+, with k(e–aq+ MV2+)= 7.5 × 1010 dm3 mol–1 s–1, leads to the formation of the long-lived radical cation (MV˙+), which possesses two absorption maxima at 392.5 nm (Iµ392.5= 4200 m2 mol–1) and 600 nm (Iµ600= 1450 m2 mol–1). The H-atoms react with MV2+ at pH 1 forming two species, which have superimposed absorption bands. By means of a computer simulation they are resolved in the absorptions belonging to: (1) a protonated form of the radical cation (MV˙+H+), which is produced with k(H + MV2+)=(3.5 ± 0.2)× 108 dm3 mol–1 s–1, has 2 absorption maxima at 390 nm (Iµ390= 1700 m2 mol–1) and 595 nm (Iµ595= 760 m2 mol–1) and decays by second-order kinetics with k= 3.5 × 109 dm3 mol–1 s–1; (2) an H-adduct (MV˙2+H) on the ring carbon, which is formed with k(H + MV2+)= 2.5 × 108 dm3 mol–1 s–1, absorbs at 310 nm (Iµ310= 900 m2 mol–1) and 470 nm (Iµ470= 630 m2 mol–1) and decays by conversion into MV˙+H+ in a first-order process with k= 6 × 103 s–1. For the equilibrium MV˙+H+⇌ MV˙++ H+ pK= 2.9 ± 0.1 was determined. The presented data explain, at least partly, the instability of MV2+ when used as an electron acceptor in various devices for the utilization of solar energy.

The reaction mechanism and rate constants in the radiolysis of Fe2+-Cu2+ solutions.

G({rm H}_{2}{rm O}_{2})

Rate constants of OH with HO2,O2-, and H2O2+ from hydrogen peroxide formation in pulse-irradiated oxygenated water

was measured in aqueous solutions containing different low concentrations of

Ultraviolet Spectrum and Decay of the Ozonide Ion Radical, O3, in Strong Alkaline Solution

{rm O}_{2}+{rm Br}^{-}

Dissociation of the OH Adduct of N,N-Dimethylaniline in Aqueous Solution

and

Input Files for Computer Simulation of Water Radiolysis

G({rm H}_{2})

THE

was measured in dilute solutions of KBr at d...

sup 60

Pulse radiolysis and gamma radiolysis have been used to study the reaction mechanism in the radiolysis of aqueous solutions of Fe/sup 2 +/ and Cu/sup 2 +/. A reaction scheme has been developed and confirmed by computation of the corresponding complete set of differential equations. The rate constants for some of the reactions have been determined at different pHs. k/sub Cu/sup +/ + O/sub 2// = 4.6 x 10/sup 5/ and 1.0 x 10/sup 6/ mol/sup -1/ sec/sup -1/, k/sub Cu/sup +/ + Fe/sup 3 +// = 5.5 x 10/sup 6/ and 1.3 x 10/sup 7/ mol/sup -1/ sec/sup -1/, k/sub Cu(III) + Fe/sup 2 +// = 3.3 x 10/sup 8/ and 1.3 x 10/sup 8/ mol/sup -1/ sec/sup -1/ in pH 2.1 H/sub 2/SO/sub 4/ and HClO/sub 4/, respectively.