Statistical mechanics of hydrated electron recombination in liquid and supercritical water

The photochemical yield of hydrated electrons as a function of temperature in liquid and supercritical water is treated in terms of energy fluctuations of the medium. The geminate pair, consisting of a positive ion and a hydrated electron, is regarded as a H-like atom embedded in a completely relaxed dielectric continuum. If the local medium energy is larger than the ionization energy of this atom, the electron escapes its geminate partner. By making use of the classical theory of energy fluctuations, escape probability is described by a simple explicit function, the variable of which is a combination of temperature, relative permittivity, and specific heat. First our earlier calculations on the recombination of solvated electrons, produced by ionizing radiation in a number of polar liquids, are improved and then the theory is compared with the experimental results on temperature dependent electron survival by Kratz et al. [S. Kratz, J. Torres-Alcan, J. Urbanek, J. Lindner, and P. Vo?hringer, Phys. Chem. Chem. Phys. 12, 12169 (2010)]. Two adjustable parameters are needed to achieve reasonable quantitative agreement.     

A new high-temperature multinuclear-magnetic-resonance probe and the self-diffusion of light and heavy water in sub- and supercritical conditions

A high-resolution nuclear-magnetic-resonance probe (500 MHz for 1H) has been developed for multinuclear pulsed-field-gradient spin-echo diffusion measurements at high temperatures up to 400 degrees C. The convection effect on the self-diffusion measurement is minimized by achieving the homogeneous temperature distributions of +/-1 and +/-2 degrees C, respectively, at 250 and 400 degrees C. The high temperature homogeneity is attained by using the solid-state heating system composed of a ceramic (AlN) with high thermal conductivity comparable with that of metal aluminium. The self-diffusion coefficients D for light (1H2O) and heavy (2H2O) water are distinguishably measured at subcritical temperatures of 30-350 degrees C with intervals of 10-25 degrees C on the liquid-vapor coexisting curve and at a supercritical temperature of 400 degrees C as a function of water density between 0.071 and 0.251 gcm3. The D value obtained for 1H2O is 10%-20% smaller than those previously reported because of the absence of the convection effect. At 400 degrees C, the D value for 1H2O is increased by a factor of 3.7 as the water density is reduced from 0.251 to 0.071 gcm3. The isotope ratio D(1H2O)D(2H2O) decreases from 1.23 to approximately 1.0 as the temperature increases from 30 to 400 degrees C. The linear hydrodynamic relationship between the self-diffusion coefficient divided by the temperature and the inverse viscosity does not hold. The effective hydrodynamic radius of water is not constant but increases with the temperature elevation in subcritical water.     

Nanosecond kinetics of hydrated electrons upon water photolysis by high intensity femtosecond UV pulses

We report a nanosecond laser study of the transient absorption of hydrated electrons generated by multiphoton ionisation of liquid water upon excitation at 266 and 400 nm by femtosecond pulses with power densities higher than 1 TW/cm². For both wavelengths, as the pump power density increases, the signal amplitude increases and the decay becomes faster proving that more electrons are produced. However, we show that in the nanosecond time range, under pump power densities higher than 1 TW/cm², the distribution of the hydrated electrons is not uniform along the optical pathway of the pump beam in the water sample.     

Photohydroxylation of 1,4-benzoquinone in aqueous solution revisited

In water, photolysis of 1,4-benzoquinone, Q gives rise to equal amounts of 2-hydroxy-1,4-benzoquinone HOQ and hydroquinone QH(2) which are formed with a quantum yield of Phi=0.42, independent of pH and Q concentration. By contrast, the rate of decay of the triplet (lambda(max)=282 and approximately 410 nm) which is the precursor of these products increases nonlinearly (k=(2-->3.8) x 10(6) s(-1)) with increasing Q concentration ((0.2-->10) mM). The free-radical yield detected by laser flash photolysis after the decay of the triplet also increases with increasing Q concentration but follows a different functional form. These observations are explained by a rapid equilibrium of a monomeric triplet Q* and an exciplex Q(2)* (K=5500+/-1000 M(-1)). While Q* adds water and subsequent enolizes into 1,2,4-trihydroxybenzene Ph(OH)(3), Q(2)* decays by electron transfer and water addition yielding benzosemiquinone (.)QH and (.)OH adduct radicals (.)QOH. The latter enolizes to the 2-hydroxy-1,4-semiquinone radical (.)Q(OH)H within the time scale of the triplet decay and is subsequently rapidly (microsecond time scale) oxidized by Q to HOQ with the concomitant formation of (.)QH. On the post-millisecond time scale, that is, when (.)QH has decayed, Ph(OH)(3) is oxidized by Q yielding HOQ and QH(2) as followed by laser flash photolysis with diode array detection. The rate of this pH- and Q concentration-dependent reaction was independently determined by stopped-flow. This shows that there are two pathways to photohydroxylation; a free-radical pathway at high and a non-radical one at low Q concentration. In agreement with this, the yield of Ph(OH)(3) is most pronounced at low Q concentration. In the presence of phosphate buffer, Q* reacts with H(2)PO(4) (-) giving rise to an adduct which is subsequently oxidized by Q to 2-phosphato-1,4-benzoquinone QP. The current view that (.)OH is an intermediate in the photohydroxylation of Q has been overturned. This view had been based on the observation of the (.)OH adduct of DMPO when Q is photolyzed in the presence of this spin trap. It is now shown that Q*/Q(2)* oxidizes DMPO (k approximately 1 x 10(8) M(-1) s(-1)) to its radical cation which subsequently reacts with water. Q*/Q(2)* react with alcohols by H abstraction (rates in units of M(-1) s(-1)): methanol (4.2 x 10(7)), ethanol (6.7 x 10(7)), 2-propanol (13 x 10(7)) and tertiary butyl alcohol ( approximately 0.2 x 10(7)). DMSO (2.7 x 10(9)) and O(2) ( approximately 2 x 10(9)) act as physical quenchers.     

Microhydration of Cs+ ion: a density functional theory study on Cs+-(H2O)n clusters (n=1-10)

Structure, energy enthalpy, and IR frequency of hydrated cesium ion clusters, Cs+-(H2O)n (n=1-10), are reported based on all electron calculations. Calculations have been carried out with a hybrid density functional, namely, Becke's three-parameter nonlocal hybrid exchange-correlation functional B3LYP applying cc-PVDZ correlated basis function for H and O atoms and a split valence 3-21G basis function for Cs atom. Geometry optimizations for all the cesium ion-water clusters have been carried out with several possible initial guess structures following Newton-Raphson procedure leading to many conformers close in energy. The calculated values of binding enthalpy obtained from present density functional based all electron calculations are in good agreement with the available measured data. Binding enthalpy profile of the hydrated clusters shows a saturation behavior indicating geometrical shell closing in hydrated structure. Significant shifts of O-H stretching bands with respect to free water molecule in IR spectra of hydrated clusters are observed in all the hydrated clusters.     

Acetone hydration in supercritical water: (13)C-NMR spectroscopy and Monte Carlo simulation

The (13)C-NMR chemical shift of acetone delta((13)C[Double Bond]O) was measured in aqueous solution at high temperatures up to 400 degrees C and water densities of 0.10-0.60 g/cm(3) for the study of hydration structure in the supercritical conditions. The average number N(HB) of hydrogen bonds (HBs) between an acetone and solvent waters and the energy change DeltaE upon the HB formation were evaluated from the delta and its temperature dependence, respectively. At 400 degrees C, N(HB) is an increasing function of the water density, the increase being slower at higher water densities. The acetone-water HB formation is exothermic in supercritical water with larger negative DeltaE at lower water densities (-3.3 kcal/mol at 0.10 g/cm(3) and -0.3 kcal/mol at 0.60 g/cm(3)), in contrast to the positive DeltaE in ambient water (+0.078 kcal/mol at 4 degrees C). The corresponding Monte Carlo simulations were performed to calculate the radial and orientational distribution functions of waters around the acetone molecule. The density dependence of N(HB) calculated at 400 degrees C is in a qualitative agreement with the experimental results. In the supercritical conditions, the HB angle in a neighboring acetone-water pair is weakly influenced by the water density, because of the absence of collective HB structure. This is in sharp contrast to the hydration structure in ambient water, where the acetone-water HB formation is orientationally disturbed by the tetrahedral HB network formation among the surrounding waters.     

Microsolvation effect, hydrogen-bonding pattern, and electron affinity of the uracil-water complexes U-(H2O)n (n = 1, 2, 3)

To achieve a systematic understanding of the influence of microsolvation on the electron accepting behaviors of nucleobases, the reliable theoretical method (B3LYP/DZP++) has been applied to a comprehensive conformational investigation on the uracil-water complexes U-(H(2)O)(n) (n = 1, 2, 3) in both neutral and anionic forms. For the neutral complexes, the conformers of hydration on the O2 of uracil are energetically favored. However, hydration on the O4 atom of uracil is more stable for the radical anions. The electron structure analysis for the H-bonding patterns reveal that the CH...OH(2) type H-bond exists only for di- and trihydrated uracil complexes in which a water dimer or trimer is involved. The electron density structure analysis and the atoms-in-molecules (AIM) analysis for U-(H(2)O)(n) suggest a threshold value of the bond critical point (BCP) density to justify the CH...OH(2) type H-bond; that is, CH...OH(2) could be considered to be a H-bond only when its BCP density value is equal to or larger than 0.010 au. The positive adiabatic electron affinity (AEA) and vertical detachment energy (VDE) values for the uracil-water complexes suggest that these hydrated uracil anions are stable. Moreover, the average AEA and VDE of U-(H(2)O)(n) increase as the number of the hydration waters increases.     

Density dependence of the "escape" yield of hydrated electrons in the low-LET radiolysis of supercritical water at 400 °C

The "spur lifetime" (τ(s)) in the low-linear energy transfer (LET) radiolysis of supercritical water (SCW) at 400 °C has been determined as a function of water density by using a simple model of energy deposition initially in spurs, followed by the random diffusion (Brownian motion) of the species formed until spur expansion is complete. The values of τ(s) are found to decrease from ～5.0 × 10(-6) to 5.0 × 10(-8) s over the density range from 0.15 to 0.6 g cm(-3). Using Monte-Carlo simulations, our calculated density dependence of the "escape" hydrated electron (e(aq)(-)) yield (i.e., at time τ(s)) reproduces fairly well Bartels and co-workers' scavenged e(aq)(-) yield data, suggesting that these data may have been measured at times close to τ(s).     

Radiolysis of aqueous solutions of 1,1- and 1,2-dichloroethane

The yields of chloride ion and molecular hydrogen were determined in the gamma, the fast electron, and the 5 MeV helium ion radiolysis of deaerated and aerated aqueous solutions of 1,1- and 1,2-dichloroethane. In deaerated solutions irradiated with gamma-rays or fast electrons, the yield of chloride ion increases while the yield of molecular hydrogen decreases with increasing dichloroethane concentration. These results are due to the quantitative reaction of both the hydrated electron and the hydrogen atom with the dichloroethane to produce chloride ions. The yield of chloride ions is significantly larger in aerobic than in anaerobic conditions and is dependent upon the dose rate. Formation of peroxyl radicals by the reaction of molecular oxygen with chlorinated hydrocarbon radicals and their subsequent chemistry are responsible for the observed increase in chloride ions. The yield of chloride ion with 5 MeV helium ions is smaller than with gamma irradiation, while the yield of molecular hydrogen is larger reflecting the higher density of reactive species and consequent increase in intratrack reactions in a helium ion track compared to a gamma-ray track.     

Radiolysis of confined water: molecular hydrogen formation.

The formation of molecular hydrogen in the radiolysis of water confined in nanoscale pores of well-characterised porous silica glasses and mesoporous molecular sieves (MCM-41) is examined. The comparison of dihydrogen formation by irradiation of both materials, dry and hydrated, shows that a large part of the H2 comes from the surface of the material. The radiolytic yields, G(H2)=(3+/-0.5)x10(-7) mol J(-1), calculated using the total energy deposited in the material and the water, are only slightly affected by the degree of hydration of the material and by the pore size. These yields are also not modified by the presence of hydroxyl radical scavengers. This observation proves that the back reaction between H2 and HO(.) is inoperative in such confined environments. Furthermore, the large amount of H2 produced in the presence of different concentrated scavengers of the hydrated electron and its precursor suggests that these two species are far from being the only species responsible for the H2 formation. Our results show that the radiolytic phenomena that occur in water confined in nanoporous silica are dramatically different to those in bulk water, suggesting the need to investigate further the chemical reactivity in this type of environment.     

Radiolysis of confined water: hydrogen production at a high dose rate.

The production of molecular hydrogen in the radiolysis of dried or hydrated nanoporous controlled-pore glasses (CPG) has been carefully studied using 10 MeV electron irradiation at high dose rate. In all cases, the H2 yield increases when the pore size decreases. Moreover, the yields measured in dried materials are two orders of magnitude smaller than those obtained in hydrated glasses. This proves that the part of the H2 coming from the surface of the material is negligible in the hydrated case. Thus, the measured yields correspond to those of nanoconfined water. Moreover, these yields are not modified by the presence of potassium bromide, which is a hydroxyl radical scavenger. This experimental observation shows that the back reaction between H2 and HO* does not take place in such confined environments. These porous materials have been characterized before and after irradiation by means of Fourier-transform infrared (FT-IR) spectroscopy, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) techniques, which helps to understand the elementary processes taking place in this type of environment, especially the protective effect of water on the surface in the case of hydrated glasses.     

Pulse radiolysis based on a femtosecond electron beam and a femtosecond laser light with double-pulse injection technique

A new pulse radiolysis system based on a femtosecond electron beam and a femtosecond laser light with oblique double-pulse injection was developed for studying ultrafast chemical kinetics and primary processes of radiation chemistry. The time resolution of 5.2 ps was obtained by measuring transient absorption kinetics of hydrated electrons in water. The optical density of hydrated electrons was measured as a function of the electron charge. The data indicate that the double-laser-pulse injection technique was a powerful tool for observing the transient absorptions with a good signal to noise ratio in pulse radiolysis.     

Hydrogen-bond interactions in hydrated 6-selenoguanine tautomers: a theoretical study

A comprehensive theoretical investigation has been performed to study the six most stable complexes of isolated, mono, and hexahydrated 6-selenoguanine tautomers. The ground state geometries are studied at the density-functional theory and Møller–Plesset Perturbation theory implementing the 6-311++G (2d, 2p) basis set. The intermolecular distances between the water molecule and the acceptor atom of 6-selenoguanine is about 0.6 Å longer for hydrogen bonds involving selenium atom. The relative Gibbs free energy of the 6-selenoguanine tautomers favors the selenone tautomer. The majority of the stable monohydrated complexes are the one in which the oxygen atom of water accepts the acidic N7-H proton while donating a proton to the carbonyl selenium atom of 6-selenoguanine; the interaction toward N7-H being stronger than that with the selenium site. The amino group planarity has been found to be increased in the hydrated complexes. The examination of molecular orbital reveals a moderate band gap between the donor and acceptor atoms of isolated and hydrated complexes. An excellent linear correlation is found to exist between electron density and laplacian of electron density with hydrogen-bond length through atoms in molecule analysis. The natural bond orbital analysis shows a maximum charge transfer of 0.060e for selenium acceptors and around 0.025e for selenium donors.     

Transmission electron microscopy and X-Ray diffraction analysis of aluminum-induced crystallization of amorphous silicon in alpha-Si:H/Al and Al/alpha-Si:H structures.

Solid phase crystallization of plasma-enhanced chemical-vapor-deposited (PECVD) amorphous silicon (alpha-Si:H) in alpha-Si:H/Al and Al/alpha-Si:H structures has been investigated using transmission electron microscopy (TEM) and X-ray diffraction (XRD). Radiative heating has been used to anneal films deposited on carbon-coated nickel (Ni) grids at temperatures between 200 and 400 degrees C for TEM studies. alpha-Si:H films were deposited on c-Si substrates using high vacuum (HV) PECVD for the XRD studies. TEM studies show that crystallization of alpha-Si:H occurs at 200 degrees C when Al film is deposited on top of the alpha-Si:H film. Similar behavior was observed in the XRD studies. In the case of alpha-Si:H deposited on top of Al films, the crystallization could not be observed at 400 degrees C by TEM and even up to 500 degrees C as seen by XRD.     

Flash photolysis and inactivation of aqueous lysozyme

Abstract— –Flash photolysis of aqueous lysozyme has shown that the initial photochemical products are photo-oxidized tryptophan residues (Λ_max= 500 nm), hydrated electrons (Λ_max= 720 nm), and the cystine residue electron adduct (Λ_max= 420 nm). Comparisons with mixtures of the chromophoric amino acids show that 1 to 2 tryptophan residues provide electrons at a quantum yield of 0.018 (25 per cent). Part of the ejected electrons are captured by cystine residues via a short-range, intramolecular process with essentially unit efficiency. The remainder become hydrated and back react with oxidized tryptophan residues before 10^-4sec. The cystine residue electron adduct decays with 2 msec halftime (25°C) and 1.5 kcal/mole activation energy. The surviving oxidized tryptophan residues decay with a comparable time constant in a hydroxyl ion catalyzed process. In acid solutions the oxidized tryptophan residue and long-lived H atom adduct are observed (Λ_max= 380 nm). The quantum yield of lysozyme inactivation induced by xenon flash irradiation above 250 nm is 0.023 (20 per cent), which is not sensitive to oxygen or pH. Comparison to the primary photochemical reactions indicates that electron ejection from the essential tryptophan residues inactivates the enzyme, irrespective of the electron trap and subsequent reactions. On the basis of the structure and supporting information it is proposed that the tryptophan residues of the active site are involved. Direct disruption of cystine residues does not contribute more than 10 per cent to the inactivation quantum yield in this wavelength region. Lysozyme inactivation may differ from other enzymes because the chromophores include essential residues located in the active center.     

The structure of the hydrated electron. Part 2. A mixed quantum/classical molecular dynamics embedded cluster density functional theory: single-excitation configuration interaction study

Adiabatic mixed quantum/classical (MQC) molecular dynamics (MD) simulations were used to generate snapshots of the hydrated electron in liquid water at 300 K. Water cluster anions that include two complete solvation shells centered on the hydrated electron were extracted from the MQC MD simulations and embedded in a roughly 18 Ax18 Ax18 A matrix of fractional point charges designed to represent the rest of the solvent. Density functional theory (DFT) with the Becke-Lee-Yang-Parr functional and single-excitation configuration interaction (CIS) methods were then applied to these embedded clusters. The salient feature of these hybrid DFT(CIS)/MQC MD calculations is significant transfer (approximately 18%) of the excess electron's charge density into the 2p orbitals of oxygen atoms in OH groups forming the solvation cavity. We used the results of these calculations to examine the structure of the singly occupied and the lower unoccupied molecular orbitals, the density of states, the absorption spectra in the visible and ultraviolet, the hyperfine coupling (hfcc) tensors, and the infrared (IR) and Raman spectra of these embedded water cluster anions. The calculated hfcc tensors were used to compute electron paramagnetic resonance (EPR) and electron spin echo envelope modulation (ESEEM) spectra for the hydrated electron that compared favorably to the experimental spectra of trapped electrons in alkaline ice. The calculated vibrational spectra of the hydrated electron are consistent with the red-shifted bending and stretching frequencies observed in resonance Raman experiments. In addition to reproducing the visible/near IR absorption spectrum, the hybrid DFT model also accounts for the hydrated electron's 190-nm absorption band in the ultraviolet. Thus, our study suggests that to explain several important experimentally observed properties of the hydrated electron, many-electron effects must be accounted for: one-electron models that do not allow for mixing of the excess electron density with the frontier orbitals of the first-shell solvent molecules cannot explain the observed magnetic, vibrational, and electronic properties of this species. Despite the need for multielectron effects to explain these important properties, the ensemble-averaged radial wavefunctions and energetics of the highest occupied and three lowest unoccupied orbitals of the hydrated electrons in our hybrid model are close to the s- and p-like states obtained in one-electron models. Thus, one-electron models can provide a remarkably good approximation to the multielectron picture of the hydrated electron for many applications; indeed, the two approaches appear to be complementary.     

From a localized H3O radical to a delocalized H3O+···e- solvent-separated pair by sequential hydration

The impact of microhydration on the electronic structure and reactivity of the H(3)O moiety is investigated by ab initio calculations. In the gas phase, H(3)O is a radical with spin density localized on its hydrogen end, which is only kinetically stable and readily decomposes into a water molecule and a hydrogen atom. When solvated by a single water molecule, H(3)O preserves to a large extent its radical character, however, two water molecules are already capable to shift most of the spin density to the solvent. With three solvating water molecules this shift is practically completed and the system is best described as a solvent-separated pair of a hydronium cation and a hydrated electron. The electronic structure of this system and its proton transfer reactivity leading to formation of a hydrogen atom already resemble those of a proton-electron pair in bulk water.     

Theoretical studies on photoelectron and IR spectral properties of Br2.-(H2O)n clusters

We report vertical detachment energy (VDE) and IR spectra of Br2.-.(H2O)n clusters (n=1-8) based on first principles electronic structure calculations. Cluster structures and IR spectra are calculated at Becke's half-and-half hybrid exchange-correlation functional (BHHLYP) with a triple split valence basis function, 6-311++G(d,p). VDE for the hydrated clusters is calculated based on second order Moller-Plesset perturbation (MP2) theory with the same set of basis function. On full geometry optimization, it is observed that conformers having interwater hydrogen bonding among solvent water molecules are more stable than the structures having double or single hydrogen bonded structures between the anionic solute, Br2.-, and solvent water molecules. Moreover, a conformer having cyclic interwater hydrogen bonded network is predicted to be more stable for each size hydrated cluster. It is also noticed that up to four solvent H2O units can reside around the solute in a cyclic interwater hydrogen bonded network. The excess electron in these hydrated clusters is localized over the solute atoms. Weighted average VDE is calculated for each size (n) cluster based on statistical population of the conformers at 150 K. A linear relationship is obtained for VDE versus (n+3)(-1/3) and bulk VDE of Br2.- aqueous solution is calculated as 10.01 eV at MP2 level of theory. BHHLYP density functional is seen to make a systematic overestimation in VDE values by approximately 0.5 eV compared to MP2 data in all the hydrated clusters. It is observed that hydration increases VDE of bromine dimer anion system by approximately 6.4 eV. Calculated IR spectra show that the formation of Br2.--water clusters induces large shifts from the normal O-H stretching bands of isolated water keeping bending modes rather insensitive. Hydrated clusters, Br2.-.(H2O)n, show characteristic sharp features of O-H stretching bands of water in the small size clusters.     

PHOTOIONIZATION OF MELANIN PRECURSORS: AN ELECTRON SPIN RESONANCE INVESTIGATION USING THE SPIN TRAP 5,5-DIMETHYL-1-PYRROLINE-1-OXIDE (DMPO)

Abstract The photoionization of 3,4-dihydroxyphenylalanine (dopa) and catechol has been studied by electron spin resonance spectroscopy using the free radical scavenger 5,5-dimethyI-1-pyrroline-1 -oxide as a spin trap for hydrated electrons and hydrogen atoms. The photochemistry of these materials is shown to resemble tyrosine in that both photoionization and photohomolysis (to give H) occur, with photoionization predominating (by a factor of 2.6 for dopa). Ionization of one of the phenolic hydroxyl groups increases the yield of radicals by a factor of 2. Action spectra and quantum yields for radical production are reported.     

Full configuration interaction computer simulation study of the thermodynamic and kinetic stability of hydrated dielectrons

The hydrated electron is a unique solvent-supported state comprised of an excess electron that is confined to a cavity by the surrounding water. Theoretical studies have suggested that two-electron solvent-supported states also can be formed; in particular, simulations indicate that two excess electrons could pair up and occupy a single cavity, forming a so-called hydrated dielectron. Although hydrated dielectrons have not been observed directly by experiment, their existence has been posited to explain the lack of an ionic strength effect in hydrated electron bimolecular annihilation [Schmidt, K. H.; Bartels, D. M. Chem. Phys. 1995, 190, 145]. To determine whether dielectrons may be created in the laboratory, we use thermodynamic integration (TI), combined with mixed quantum/classical molecular dynamics simulation, to examine the thermodynamic stability of hydrated electrons and dielectrons. For the dielectron calculations, we solve the two-electron quantum problem using full configuration interaction. Our results suggest that hydrated dielectrons are thermodynamically unstable relative to separated (single) hydrated electrons, although we also show that increasing the pressure could drive the equilibrium toward the formation of dielectrons. Because the simulations suggest that hydrated dielectrons are kinetically stable, we also examine a scenario for creating metstable, nonequilibrium populations of dielectrons, which involves the capture of a newly injected electron by a preexisting, equilibrated hydrated electron. These calculations, which allow for the full nonadiabatic relaxation of the injected electron, show that hydrated electrons may indeed act as trapping sites for unequilibrated electrons, so that capture may be a viable mechanism for creating dielectrons. We suggest possible experimental procedures to create such nonequilibrium hydrated dielectrons using either pulse radiolysis or ultrafast spectroscopic techniques.