Optical and Chemical Measurements of Solvated Electrons Produced in Plasma Electrolysis with a Water Cathode.

It is known that glow discharges with a water anode inject and form solvated electrons at the plasma-liquid interface, driving a wide variety of reduction reactions. However, in systems with a water cathode, the production and role of solvated electrons are less clear. Here, we present evidence for the direct detection of solvated electrons produced at the interface of an argon plasma and a water cathode via absorption spectroscopy.

Exploring the Unusual Reactivity of the Hydrated Electron with CO.

Many questions remain about the reactions of the hydrated electron despite decades of study. Of particular note is that they do not appear to follow the Marcus theory of electron transfer reactions, a feature that is yet to be explained. To investigate these issues, we used molecular dynamics (AIMD) simulations to investigate one of the better studied reactions, the hydrated electron reduction of CO.

Kinetics of the Temperature-Dependent e and ⋅OH Radical Reactions with Cr(III) Ions in Aqueous Solutions.

The reactivity of chromium(III) species with the major oxidizing and reducing radiolysis products of water was investigated in aqueous solutions at temperatures up to 150 °C. The reaction between the hydrated electron (e ) and Cr(III) species showed a positive temperature dependence over this temperature range. The reaction was also studied in pH 2.

Empirically Optimized One-Electron Pseudopotential for the Hydrated Electron: A Proof-of-Concept Study.

Mixed quantum-classical molecular dynamics simulations have been important tools for studying the hydrated electron. They generally use a one-electron pseudopotential to describe the interactions of an electron with the water molecules. This approximation shows both the strength and weakness of the approach.

High-Temperature Reaction Kinetics of the e and HO Radicals with Iron(II) Ions in Aqueous Solutions.

Pulsed electron radiolysis was used to determine the chemical reaction kinetics and Arrhenius parameters for iron(II) reactions in aqueous solutions under irradiation. The second-order Fe reactions with the hydrated electron (e) and the perhydroxyl radical (HO), arising from water radiolysis, were measured to high temperatures using custom-built flow-through cells with a multichannel optical detection system. The reaction with the HO radical was found to proceed via the formation of a metal-ion adduct species, Fe-HO.

Relation between the Hydrated Electron Solvation Structure and Its Partial Molar Volume.

It is now generally accepted that the hydrated electron occupies a cavity in water, but the size of the cavity and the arrangements of the solvating water molecules have not been fully characterized. Here, we use the Kirkwood-Buff (KB) approach to examine how the partial molar volume () provides insight into these issues. The KB method relates to an integral of the electron-water radial distribution function, a key measure of the hydrated electron structure.

Reactions of Nickel Ions in Water Radiolysis up to 300 °C.

Radiation chemistry of hydrated metal ions plays a significant role in the field of nuclear energy, especially regarding water radiolysis in coolant water in nuclear reactors. This work reports new experimental data on the reactivity of Ni species under critical conditions of temperature and pressure. The reaction rates of hydrated nickel ions with water radiolysis products (e, OH, H, and HO) have been investigated for a 25-300 °C temperature range and 200 bar pressure using electron pulse radiolysis/transient absorption.

Pulse Radiolysis and Transient Absorption of Aqueous Cr(VI) Solutions up to 325 °C.

Pulse radiolysis with a custom multichannel detection system has been used to measure the kinetics of the radiation chemistry reactions of aqueous solutions of chromium(VI) to 325 °C for the first time. Kinetic traces were measured simultaneously over a range of wavelengths and fit to obtain the associated high-temperature rate coefficients and Arrhenius parameters for the reactions of Cr(VI) + , Cr(VI) + H, and Cr(V) + OH. These kinetic parameters can be used to predict the behavior of toxic Cr(VI) in models of aqueous systems for applications in nuclear technology, industrial wastewater treatment, and chemical dosimetry.

Investigation of the Failure of Marcus Theory for Hydrated Electron Reactions.

Reactions of the hydrated electron with a wide variety of substrates have been found to exhibit unusually similar activation energies in a manner incompatible with Marcus electron transfer theory. Given the fundamental linear response assumption of Marcus theory, one possible explanation for this apparent failure is that the underlying free energy surfaces governing the reactions are not harmonic; i.e.

Reactivity of Zn in high-temperature water radiolysis.

Reactivity of transients involving Zn in high-temperature water radiolysis has been studied in the temperature range of 25-300 °C. The reduced monovalent zinc species were generated from an electron transfer process between the hydrated electron and Zn ions using pulse radiolysis. The Zn species can subsequently be oxidized by the radiolytically-produced oxidizing species: ˙OH, HO and ˙H.

H Production in the B(n,α)Li Reaction in Water.

We demonstrate a method for measuring the H produced in water from the B(n,α)Li fission reaction. Low energy neutrons from the NIST Center for Neutron Research interact with borate-containing water in a temperature-controlled high pressure cell made from titanium. After exposure for one to several hours, the water is extracted and sparged with argon.

Failure of molecular dynamics to provide appropriate structures for quantum mechanical description of the aqueous chloride ion charge-transfer-to-solvent ultraviolet spectrum.

The lowest band in the charge-transfer-to-solvent ultraviolet absorption spectrum of aqueous chloride ion is studied by experiment and computation. Interestingly, the experiments indicate that at concentrations up to at least 0.25 M, where calculations indicate ion pairing to be significant, there is no notable effect of ionic strength on the spectrum.

One-electron redox kinetics of aqueous transition metal couples Zn, Co, and Ni using pulse radiolysis.

The one-electron redox potentials for aqueous metal couples Co and Ni have been investigated by using pulse radiolysis using their reactions with a series of reference compounds to establish the most positive upper limits of E. Experiments with Zn were also carried out to confirm the characteristic shape of the expected reduction kinetics. Both formate ions and t-BuOH were employed to scavenge ˙OH radicals and ˙H atoms.

Chemical Analysis of Secondary Electron Emission from a Water Cathode at the Interface with a Nonthermal Plasma.

When a nonthermal plasma and a liquid form part of the same circuit, the liquid may function as a cathode, in which case electrons are emitted from the liquid into the gas to sustain the plasma. As opposed to solid electrodes, the mechanism of this emission has not been established for a liquid, even though various theories have attempted to explain it via chemical processes in the liquid phase. In this work, we tested the effects of the interfacial chemistry on electron emission from water, including the role of pH as well as the hydroxyl radical, the hydrogen atom, the solvated electron, and the presolvated electron; it was found that none of these species are critical to sustain the plasma.

γ-Radiolysis of Room-Temperature Ionic Liquids: An EPR Spin-Trapping Study.

The radiolytic stability of a series of room-temperature ionic liquids (ILs) composed of bis(trifluoromethylsulfonyl)imide anion (TfN) and triethylammonium, 1-butyl-1-methylpyrrolidinium, trihexyl(tetradecyl)phosphonium, 1-hexyl-3-methylpyridinium, and 1-hexyl-3-methylimidazolium (hmim) cations was studied using spin-trap electron paramagnetic resonance (EPR) spectroscopy with a spin-trap α-(4-pyridyl -oxide)---butylnitrone (POBN). The trapped radical yields were measured as a function of POBN concentration and as a function of radiation dose by double integration of the broad unresolved lines. Well-resolved motionally narrowed EPR spectra for the trapped radicals were obtained by dilution of the ILs with CHCl after irradiation.

Ultraviolet charge-transfer-to-solvent spectroscopy of halide and hydroxide ions in subcritical and supercritical water.

The temperature dependence of the vacuum ultraviolet charge-transfer-to-solvent (CTTS) absorption spectra of aqueous halide and hydroxide ions was measured for the first time up to 380 °C in subcritical and supercritical water. With increasing temperature, absorption spectra are observed to broaden and redshift, much in agreement with previous measurements below 100 °C. These changes are discussed alongside classic cavity models of the solvated species, which tie in the configuration of the adjoining polarized medium and its critical role in light absorption for electronic transitions.

Partial Molar Volume of the Hydrated Electron.

The partial molar volume of the hydrated electron was investigated with pulse radiolysis and transient absorption by measuring the pressure dependence of the equilibrium constant for e + NH ⇔ H + NH. At 2 kbar pressure, the equilibrium constant decreases relative to 1 bar by only 6%. Using tabulated molar volumes for ammonia and ammonium, we have the result V̅(e) - V̅(H) = 11.

Total Internal Reflection Absorption Spectroscopy (TIRAS) for the Detection of Solvated Electrons at a Plasma-liquid Interface.

The total internal reflection absorption spectroscopy (TIRAS) method presented in this article uses an inexpensive diode laser to detect solvated electrons produced by a low-temperature plasma in contact with an aqueous solution. Solvated electrons are powerful reducing agents, and it has been postulated that they play an important role in the interfacial chemistry between a gaseous plasma or discharge and a conductive liquid. However, due to the high local concentrations of reactive species at the interface, they have a short average lifetime (~1 µs), which makes them extremely difficult to detect.

Vacuum ultraviolet spectroscopy of the lowest-lying electronic state in subcritical and supercritical water.

The nature and extent of hydrogen bonding in water has been scrutinized for decades, including how it manifests in optical properties. Here we report vacuum ultraviolet absorption spectra for the lowest-lying electronic state of subcritical and supercritical water. For subcritical water, the spectrum redshifts considerably with increasing temperature, demonstrating the gradual breakdown of the hydrogen-bond network.

Source of Molecular Hydrogen in High-Temperature Water Radiolysis.

Molecular hydrogen is a primary product of the interaction of low-LET (γ, β) radiation with water, and previous measurements have shown that its initial yield increases at elevated temperature. This has been the subject of controversy because more atomic H and (e(-))aq free radicals escape recombination at elevated temperature, and the corresponding production of H2 should decrease. Room temperature experiments have demonstrated that a large fraction of H2 also comes from early physicochemical processes (presumably electron-hole charge recombination and/or dissociative electron attachment), which can be suppressed by scavenging presolvated electrons.

Reactions of Hexa-aquo Transition Metal Ions with the Hydrated Electron up to 300 °C.

Reactions of the hydrated electron with divalent aqueous transition-metal ions, Cd(2+), Zn(2+), Ni(2+), Cu(2+), Co(2+), Fe(2+), and Mn(2+), were studied using a pulse radiolysis technique. The kinetics study was carried out at a constant pressure of 120 bar with temperatures up to 300 °C. The rate constants at room temperature agree with those reported in the literature.

A Simple ab Initio Model for the Hydrated Electron That Matches Experiment.

Since its discovery over 50 years ago, the "structure" and properties of the hydrated electron have been a subject for wonderment and also fierce debate. In the present work we seriously explore a minimal model for the aqueous electron, consisting of a small water anion cluster embedded in a polarized continuum, using several levels of ab initio calculation and basis set. The minimum energy "zero Kelvin" structure found for any 4-water (or larger) anion cluster, at any post-Hartree–Fock theory level, is very similar to a recently reported embedded-DFT-in-classical-water-MD simulation (Uhlig, Marsalek, and Jungwirth, J.

The solvation of electrons by an atmospheric-pressure plasma.

Solvated electrons are typically generated by radiolysis or photoionization of solutes. While plasmas containing free electrons have been brought into contact with liquids in studies dating back centuries, there has been little evidence that electrons are solvated by this approach. Here we report direct measurements of solvated electrons generated by an atmospheric-pressure plasma in contact with the surface of an aqueous solution.