Rate constants have been compiled for reactions of various inorganic radicals produced by radiolysis or photolysis, as well as by other chemical means in aqueous solutions. Data are included for the reactions of ⋅CO2 −, ⋅CO3⋅−, O3, ⋅N3, ⋅NH2, ⋅NO2, NO3⋅, ⋅PO32−, PO4⋅2−, SO2⋅ −, ⋅SO3 −, SO4⋅−, ⋅SO5⋅−, ⋅SeO3⋅ −, ⋅(SCN)2⋅ −, ⋅CL2⋅−, ⋅Br2⋅ −, ⋅I2⋅ −, ⋅ClO2⋅, ⋅BrO2⋅, and miscellaneous related radicals, with inorganic and organic compounds.

Rate Constants for Reactions of Inorganic Radicals in Aqueous Solution

A compilation of specific bimolecular rate constants for the reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals with inorganic and organic compounds in aqueous solution

The hydroxyl radical (•OH) is one of the most powerful oxidizing agents, able to react unselectively and instantaneously with the surrounding chemicals, including organic pollutants and inhibitors. The •OH radicals are omnipresent in the environment (natural waters, atmosphere, interstellar space, etc.), including biological systems where •OH has an important role in immunity metabolism. We provide an extensive view on the role of hydroxyl radical in different environmental compartments and in laboratory systems, with the aim of drawing more attention to this emerging issue. Further research on processes related to the hydroxyl radical chemistry in the environmental compartments is highly demanded. A comprehensive understanding of the sources and sinks of •OH radicals including their implications in the natural waters and in the atmosphere is of crucial importance, including the way irradiated chromophoric dissolved organic matter in surface waters yields •OH through the H2O2-independent pathway, and the ...

Environmental Implications of Hydroxyl Radicals ((•)OH).

The photocatalytic reduction of N₂ to NH₃ is typically hampered by poor binding of N₂ to catalytic materials and by the very high energy of the intermediates involved in this reaction. Solvated electrons directly introduced into the reactant solution can provide an alternative pathway to overcome such limitations. Here we demonstrate that illuminated hydrogen-terminated diamond yields facile electron emission into water, thus inducing reduction of N₂ to NH₃ at ambient temperature and pressure. Transient absorption measurements at 632 nm reveal the presence of solvated electrons adjacent to the diamond after photoexcitation. Experiments using inexpensive synthetic diamond samples and diamond powder show that photocatalytic activity is strongly dependent on the surface termination and correlates with the production of solvated electrons. The use of diamond to eject electrons into a reactant liquid represents a new paradigm for photocatalytic reduction, bringing electrons directly to reactants without requiring molecular adsorption to the surface.

Photo-illuminated diamond as a solid-state source of solvated electrons in water for nitrogen reduction

The role of hydroxyl radical reactions in ozonation processes in aqueous solutions

Absorption spectrum of the hydrated electron in water and in aqueous solutions

The absorption spectra of aqueous solutions after exposure to a pulse of 1.8 Mev electrons reveal a broad transient absorption band that is believed to be due to the hydrated electron, the existence and properties of which are predicted by Platzman. Aqueous ammonia solutions of various concentrations are exposed to 1.8 Mev electrons and their absorption spectra observed. The transient spectrum observed is assumed to be due to an electron trapped in the water. (D.C.W.)

Absorption Spectra in Irradiated Water and Some Solutions: Absorption Spectra of ‘Hydrated’ Electron

MANY biological materials, including bacteria, have been shown to be more readily damaged when oxygen is available to the cell at the time of irradiation than when it is absent1,2. Serratia marcescens shows this enhanced sensitivity to radiation—the so-called ‘oxygen effect’—almost to the full extent when a suspension of them is saturated with a gas mixture containing only 1 per cent oxygen and 99 per cent nitrogen, provided the radiation is given at normal dose-rates of about 1,000 rads/min. Typical inactivation curves for this organism using 1.5 MV. X-radiation from a pulsed linear accelerator are given in Fig. 1. Using the intense electron beam from the same linear accelerator, however, a dose of some 10–20 kilorads can be delivered in 2 microsec. The results quoted below indicate that when such large single pulses are used, the same bacteria saturated with the same oxygen–nitrogen mixture show the lower sensitivity corresponding to anaerobic irradiation. This is thought to be due to the fact that the first few kilorads of the electron pulse remove dissolved oxygen from the interior of the bacterium by radiation-induced reactions. During the remainder of the pulse the bacterium will thus be receiving radiation under essentially anaerobic conditions. Even though dissolved molecular oxygen may not be entirely removed by the radiation from the extracellular liquid, this cannot penetrate the cell by diffusion in the 2 microsec. that the pulse lasts.

J. W. Boag

Papers

Absorption spectrum of the hydrated electron in water and in aqueous solutions

Absorption Spectra in Irradiated Water and Some Solutions: Absorption Spectra of ‘Hydrated’ Electron

Modification of the oxygen effect when bacteria are given large pulses of radiation

Reactions of the hydroxyl radical. Part 2.—Determination of absolute rate constants

Spectroscopic studies of reactions of the OH radical in aqueous solutions. Reaction of OH with the ferrocyanide ion