Pulse Radiolysis Of Water Research Articles

Transient Raman spectra, structure, and thermochemistry of the thiocyanate dimer radical anion in water.

Time-resolved resonance-enhanced Stokes and anti-Stokes Raman spectra of the thiocyanate dimer radical anion, (SCN)2•-, prepared by pulse radiolysis in water, have been obtained and interpreted in conjunction with theoretical calculations to provide detailed information on the molecular geometry and bond properties of the species. The structural properties of the radical are used to develop a molecular perspective on its thermochemistry in an aqueous solution. Twenty-nine Stokes Raman bands of the radical observed in the 120-4200 cm-1 region are assigned in terms of the strongly enhanced 220 cm-1 fundamental, weakly enhanced 721 cm-1, and moderately enhanced 2073 cm-1 fundamentals, their overtones, and combinations. Calculations by range-separated hybrid density functionals (ωB97x and LC-ωPBE) support the spectroscopic assignments of the 220 cm-1 vibration to a predominantly SS stretching mode and the features at 721 cm-1 and 2073 cm-1 to CS and CN symmetric stretching modes, respectively. The corresponding bond lengths are 2.705 (±0.036) Å, 1.663 (±0.001) Å, and 1.158 (±0.002) Å. A first order anharmonicity of 1 cm-1 determined for the SS stretching mode suggests a convergence of vibrational states at an energy of ∼1.5 eV, using the Birge-Sponer extrapolation. This value, estimated for the radical confined in solvent cage, compares well with the calculated gas-phase energy of 1.26 ± 0.04 eV required for the radical to dissociate into SCN• and SCN- fragments. The enthalpy of dissociation drops to 0.60 ± 0.03 eV in water when solvent dielectric effects on the radical and its dissociation products upon S-S bond scission are incorporated in the calculations. No frequency shift or spectral broadening was observed between light and heavy water solvents, indicating that the motion of solvent molecules in the hydration shell has no perceptible effect on the intramolecular dynamics of the radical. The Stokes and anti-Stokes Raman frequencies were found to be identical within the experimental uncertainty, suggesting that the frequency difference between the thermally relaxed and spontaneously created vibrational states of (SCN)2•- in water is too small to be observable.

Isotope Dependence and Quantum Effects on Atomic Hydrogen Diffusion in Liquid Water.

Relative diffusion coefficients were determined in water for the D, H, and Mu isotopes of atomic hydrogen by measuring their diffusion-limited spin-exchange rate constants with Ni(2+) as a function of temperature. H and D atoms were generated by pulse radiolysis of water and measured by time-resolved pulsed EPR. Mu atoms are detected by muonium spin resonance. To isolate the atomic mass effect from solvent isotope effect, we measured all three spin-exchange rates in 90% D2O. The diffusion depends on the atomic mass, demonstrating breakdown of Stokes-Einstein behavior. The diffusion can be understood using a combination of water "cavity diffusion" and "hopping" mechanisms, as has been proposed in the literature. The H/D isotope effect agrees with previous modeling using ring polymer molecular dynamics. The "quantum swelling" effect on muonium due to its larger de Broglie wavelength does not seem to slow its "hopping" diffusion as much as predicted in previous work. Quantum effects of both the atom mass and the water librations have been modeled using RPMD and a qTIP4P/f quantized flexible water model. These results suggest that the muonium diffusion is very sensitive to the Mu versus water potential used.

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

Understanding the properties of hydrated electrons, which were first observed using pulse radiolysis of water in 1962, is crucial because they are key species in many radiation chemistry processes. Although time-resolved spectroscopic studies and molecular simulations have shown that an electron in water (prepared, for example, by water photoionization) relaxes quickly to a localized, cavity-like structure ∼2.5 Å in radius, this picture has recently been questioned. In another experimental approach, negatively charged water clusters of increasing size were studied with photoelectron and IR spectroscopies. Although small water clusters can bind an excess electron, their character is very different from bulk hydrated species. As data on electron binding in liquid water have become directly accessible experimentally, the cluster-to-bulk extrapolations have become a topic of lively debate. Quantum electronic structure calculations addressing experimental measurables have, until recently, been largely limited to small clusters; extended systems were approached mainly with pseudopotential calculations combining a classical description of water with a quantum mechanical treatment of the excess electron. In this Account, we discuss our investigations of electrons solvated in water by means of ab initio molecular dynamics simulations. This approach, applied to a model system of a negatively charged cluster of 32 water molecules, allows us to characterize structural, dynamical, and reactive aspects of the hydrated electron using all of the system's valence electrons. We show that under ambient conditions, the electron localizes into a cavity close to the surface of the liquid cluster. This cavity is, however, more flexible and accessible to water molecules than an analogous area around negatively charged ions. The dynamical process of electron attachment to a neutral water cluster is strongly temperature dependent. Under ambient conditions, the electron relaxes in the liquid cluster and becomes indistinguishable from an equilibrated, solvated electron on a picosecond time scale. In contrast, for solid, cryogenic systems, the electron only partially localizes outside of the cluster, being trapped in a metastable, weakly bound "cushion-like" state. Strongly bound states under cryogenic conditions could only be prepared by cooling equilibrated, liquid, negatively charged clusters. These calculations allow us to rationalize how different isomers of electrons in cryogenic clusters can be observed experimentally. Our results also bring into question the direct extrapolation of properties of cryogenic, negatively charged water clusters to those of electrons in the bulk liquid. Ab initio molecular dynamics represents a unique computational tool for investigating the reactivity of the solvated electron in water. As a prototype, the electron-proton reaction was followed in the 32-water cluster. In accord with experiment, the molecular mechanism is a proton transfer process that is not diffusion limited, but rather controlled by a proton-induced deformation of the excess electron's solvent shell. We demonstrate the necessary ingredients of a successful density functional methodology for the hydrated electron that avoids potential pitfalls, such as self-interaction error, insufficient basis set, or lack of dispersion interactions. We also benchmark the density functional theory methods and outline the path to faithful ab initio simulations of dynamics and reactivity of electrons solvated in extended aqueous systems.

Pulse radiolysis in water with heavy-ion beams. A short review

This article presents a short review of the studies in radiation chemistry of liquid water with heavy ions, which have used pulse radiolysis methods during the last 20 years. The interests and the difficulties of developing this kind of experiment are depicted. The linear energy transfer (LET) effect is the main topic of these studies. The earliest effects close to the structure of the deposited energy can be observed directly by transient absorption spectroscopy by following the hydrated electron, the superoxide radical produced in the absence of molecular oxygen and the hydroxyl radical, which still requires the use of scavenger. Finally, the results can be compared to the heterogeneous chemical processes in the time range of 1 ns to 1 μs described by Monte Carlo simulations. The absolute values of the radiolytic yields are still uncertain because of the dosimetry accuracy. The future aspects of the method are discussed in terms of new types of particle accelerators giving better time resolutions.

H-atom abstraction from thiols by C-centered radicals. A theoretical and experimental study of reaction rates

The Arrhenius parameters and rates of reaction of three hydroxyradicals, methyl radical, and the hindered primary C-centred radical from t-butyl alcohol with dithiothreitol were measured by pulse radiolysis in water. The bimolecular rate constants were found to be in the order: ˙C(CH3)2OH > ˙CH(CH3)OH > ˙CH2OH > ˙CH3 > ˙CH2C(CH3)2OH. The reaction of three of these, ˙C(CH3)2OH, ˙CH2OH, and ˙CH3, with methanethiol were examined at the ab initio B3LYP/6311+G(d,p) level, coupled with transition state theory, both in the gas phase and in solution. The solvent effects are evaluated by two different continuum models (SCIPCM, CPCM), coupled with a novel approach to the calculation of the solution phase entropy. The reaction is discussed in terms of the charge and spin polarization in the transition state, as determined by AIM analysis, and in terms of orbital interaction theory. Rate constants, calculated by transition state theory are in good agreement with the experimental data.

One-electron reduction potential and ring opening of the succinimidyl radical in water

By means of pulse radiolysis in water, N-chlorosuccinimide (SCl) was reduced in a one-electron step to yield the succinimidyl radical, S . , via the intermediacy of the radical anion, SCl .- . The rate of ring opening of S . was measured to be 8×10 4 s -1 . By equilibration with Cl 2 .- /2Cl - , the one-electron reduction potential of S . was determined to be 2.22±0.02 V vs NHE

The reaction of ethidium bromide with oxidising free radicals: Pulse radiolysis in water and DNA

Pulse radiolysis has been used to study the reaction of ethidium bromide with Br 2 -, (SCN) 2 - and N 2, both in aqueous solution and in aqueous solutions of DNA. Rate constants of 1.9 ± 0.2, 1.8 ± 0.2 and 5.7 ± 0.6 x 10 9 M -1s -1 were measured for Br 2 -, (SCN) 2 - and N 2 respectively in aqueous solution. The rate constant for reaction of Br 2 - and (SCN) 2 - with ethidium bromide is reduced by a factor of approximately 1000 when the dye is intercalated in DNA, whilst the reduction is only a factor of 50 for N 2. The product of these reactions is one electron oxidised ethidium bromide, which is shown to undergo a deprotonation reaction in alkaline solution. A pK value of 8.2 ± 0.3 is measured for oxidised ethidium bromide in aqueous solution and this value does not change appreciably in the presence of DNA. Possible implications of these observations are discussed.

Pulse-radiolysis study of the reduction of oxovanadium(2+) by the hydrated electron

A study of the reduction of VO/sup 2 +/ by the hydrated electron from the pulse-radiolysis of water was undertaken to determine if a process similar to that observed for the reaction with NpO/sup 2 +/ was controlling the reaction. The reaction was studied in the pH range of 3.8 - 4.6. The conductivity data of the aqueous solutions were analyzed by computer programs. From excellent agreement between the measured and calculated decay rates and signal amplification, it was concluded that a (H/sup +/)- independent rearrangement reaction was not necessary to interpret the experimental results. These conclusions indicate a marked difference between the reactions of Np and V. 14 references, 1 figure.

The sign of electron exchange in random radical encounter pairs

The electron spin polarization pattern observed in independently generated radicals (F-pairs) produced by both laser photolysis and pulse radiolysis in water, alcoholic, and hydrocarbon solvents is E/A, low-field emission, high-field enhanced absorption. Thus, the sign of the exchange coupling in F-pairs is negative contrary to the recent suggestion that exchange coupling is positive in F-pairs.

Effects of pulse dose on hydrated electron decay kinetics in the pulse radiolysis of water. A computer modeling study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTEffects of pulse dose on hydrated electron decay kinetics in the pulse radiolysis of water. A computer modeling studyConrad N. Trumbore, David R. Short, James E. Fanning Jr., and Jon H. OlsonCite this: J. Phys. Chem. 1978, 82, 26, 2762–2767Publication Date (Print):December 1, 1978Publication History Published online1 May 2002Published inissue 1 December 1978https://doi.org/10.1021/j100515a002RIGHTS & PERMISSIONSArticle Views103Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (812 KB) Supporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Evidence for spur overlap in the pulse radiolysis of water

The kinetics of the decay of hydrated electron absorbance in pure water has been studied as a function of time and radiation dose delivered by 20-ns pulses of 15-MeV electrons. In order to identify intraspur reactions of the hydrated electron, values of the function ((-d(e/sub aq//sup -/)/(e/sub aq//sup -/))/dt)/sub t/ (identical with Q/sub t/) were investigated as a function of pulse dose and time. Q/sub t/ represents the fraction of hydrated electrons disappearing at any given time, t, following the pulse. Whereas Q has the same functional form as a first-order rate constant, it is not a constant, but decreases with increasing time following the pulse. However, the functional form of Q/sub t/ vs. time remains the same at low pulse doses (37 - 380 rads) for relatively long periods of time (up to 1 ..mu..s). The dose independence of Q is interpreted as evidence for predominantly intraspur hydrated electron decay. A plot of Q/sub t/ vs. the function ((time)/sup 1/2/(dose)/sup 1/3)) yields a relatively sharp transition from dose independent hydrated electron decay (interpreted as arising predominantly from intraspur reactions) to dose dependent decay (both interspur and intraspur decay). This transition region is interpreted as the onset of significant spurmore » overlap. In the range 0-8000 rads per 20-ns pulse, an empirical constant: (approximate time of detectable overlap)/sup 1/2/ (dose)/sup 1/3/ = 110 +- 10 ns/sup 1/2/ rads/sup 1/3/ is obtained which correlates the onset of experimentally observable spur overlap. Based upon these results, implications regarding spur sizes and spatial distributions of spurs and the need to include spur overlap considerations in modeling studies are developed.« less

EPR Pulse Radiolysis Studies of the Hydrogen Atom in Aqueous Solution. I. Reactivity of the Hydrogen Atom

The transient properties of hydrogen and deuterium atoms produced by pulse radiolysis in water have been studied by EPR. Details of the EPR instrumentation are described. From decay characteristics of the EPR signal on addition of various solutes, rate constants for the reaction of atomic hydrogen with various classes of molecules have been determined. Agreement of our results with prior indirect determinations is, in general, good. The isotope effect is also in agreement with expectation.

Cerenkov radiation from the pulse radiolysis of water

Luminescence has been observed from water irradiated with a very intense 20 ns pulse of 0·5 MeV electrons. The angular distribution, visible spectrum, electron energy dependence, lifetime and photon yield of the light emission have been determined. The influence of a few solutes on the luminescence has been investigated. In addition the emission was compared with that from methanol, benzene and cyclohexane. All of these data indicate that at least 90 per cent of the luminescence in the visible spectrum is Cerenkov radiation and that the fluorescence or phosphorescence yields from water must have G( hv)⪡10 −3. A combination of the Bethe stopping power relation with the Frank-Tamm theory of Cerenkov radiation is shown to account satisfactorily for the electron energy dependence of the emission. From the equation so derived the total number of photons between 4000 and 6000 Å per incident electron is estimated to be 3·8, in agreement with the experimental value.

Pulse Radiolysis

Pulse Radiolysis of Water and Aqueous Solutions By A. K. Pikaev. Translated by Scripta Technica, Inc. Translation edited by Edwin J. Hart. English edition revised and augmented by the author. Pp. xvi + 295. (Bloomington and London: Indiana University Press, 1967.) 75s.