Yield Of Solvated Electrons Research Articles

Mechanism for plasmon-generated solvated electrons

Solvated electrons are powerful reducing agents capable of driving some of the most energetically expensive reduction reactions. Their generation under mild and sustainable conditions remains challenging though. Using near-ultraviolet irradiation under low-intensity one-photon conditions coupled with electrochemical and optical detection, we show that the yield of solvated electrons in water is increased more than 10 times for nanoparticle-decorated electrodes compared to smooth silver electrodes. Based on the simulations of electric fields and hot carrier distributions, we determine that hot electrons generated by plasmons are injected into water to form solvated electrons. Both yield enhancement and hot carrier production spectrally follow the plasmonic near-field. The ability to enhance solvated electron yields in a controlled manner by tailoring nanoparticle plasmons opens up a promising strategy for exploiting solvated electrons in chemical reactions.

Direct Observation of Solvated Electrons in Deep Eutectic Solvents: Efficient Capture of Presolvated Electrons by DNA Base.

The solvated electron being the simplest form of an extremely reactive intermediate is of great fundamental interest in chemistry, physics, and biology since its discovery. Recently, deep eutectic solvents (DESs) have been in focus as biodegradable and cost-effective alternative to ionic liquids (ILs) for different applications. These include areas where electron transport and transfer processes are involved. Herein, we present the first report on the existence, yield, and properties of solvated electrons in three deep eutectic solvents, reline, ethaline, and glyceline, composed of choline chloride as a hydrogen bond acceptor and urea, ethylene glycol, and glycerol (Gly) as hydrogen bond donors, respectively, at a molar ratio of 1:2. The varied transient absorption spectra of solvated electrons in these DESs have been explained on the basis of polarity, hydrogen-bonding effect, and the moieties responsible for creating the environment for solvation. The yield and average lifetime follow the trends in viscosity as well as the reactivity of electrons with the components. The C37 value, a measure of the efficiency of scavenging presolvated electrons, is the highest in ethaline in the case of nitrate ions, which indicates the slowest solvation process in this DES. The presolvated electron capture by a DNA base, an aspect considered to be important in cancer radiotherapy, could be monitored conveniently in these liquids at a much longer time scale compared to that reported in aqueous solutions. Bimolecular rate constants for the reaction of solvated electrons with nitrate and the DNA base have been calculated and compared in the three DESs. Unlike in ILs, these experimentally obtained values are comparable to the diffusion-controlled rate constants in DESs.

Experimental investigation of picosecond dynamics following interactions between laser accelerated protons and water

We report direct experimental measurements with picosecond time resolution of how high energy protons interact with water at extreme dose levels (kGy), delivered in a single pulse with the duration of less than 80 ps. The unique synchronisation possibilities of laser accelerated protons with an optical probe pulse were utilized to investigate the energy deposition of fast protons in water on a time scale down to only a few picoseconds. This was measured using absorbance changes in the water, induced by a population of solvated electrons created in the tracks of the high energy protons. Our results indicate that for sufficiently high doses delivered in short pulses, intertrack effects will affect the yield of solvated electrons. The experimental scheme allows for investigation of the ultrafast mechanisms occurring in proton water radiolysis, an area of physics especially important due to its relevance in biology and for proton therapy.

Radiolytic yields of solvated electrons in ionic liquid and its solvation dynamics at low temperature

We present an investigation of the solvated electron in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (P14NTf2) using pulse radiolytic techniques. Temperature-dependent studies reveal that the yield of the solvated electron decreases with decreasing temperature. The lower initial yield measured indicates that we have a loss of some electrons before they become fully solvated. There may be a high probability that the excess dry electrons (pre-solvated electron) react before the electron solvation is completed because the solvation dynamics is slowing down with decreasing temperature.

Improvement of Radiation Resistance and an Estimate of Solvated Electron Yield of the Ionic Liquid [Bmim]Cl by the Addition of FeCl3

The radiation stability of the ionic liquid 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) was investigated after (60)Co γ irradiation at doses up to 600 kGy. Thermal and spectroscopic analysis revealed the formation of a small quantity of radiolytic products and an evident change in the physicochemical properties of the ionic liquid. The presence of anionic FeCl(4)(-) (up to 5 mol%), as measured by UV-vis absorption, differential scanning calorimetry, and Raman spectroscopy, significantly improved the radiation resistance of [Bmim]Cl. The increased resistance may be due to the capture of a solvated electron (e(solv)(-)) by FeCl(4)(-) to form FeCl(4)(2-) and results in the radiation protection of the organic cation. The radiation yield of the reductive species (Fe(II)) was estimated to be 0.217 ± 0.010 µmol/J (2.09 ± 0.10/100 eV), which is considered close to the radiation yield of the solvated electrons of [Bmim]Cl.

Electron emission from photo-excited testosterone in water–ethanol solution

Testosterone (TES; 4-androstene-17β-ol-3-on) is found for the first time to eject electrons from its singlet excited state in water–ethanol solvent mixture. This ability was very recently also observed for 17β-estradiol (17βE2) and progesterone (PRG)/1/. With increasing TES-concentration, the yield of solvated electrons ( e s - ) is decreasing, because of “associate” formation. At higher absorbed UV-doses ( λ = 254 nm) the e s - yield is passing a sharp maximum by formation of TES–ethanol adducts, which are able likewise to emit electrons when excited. At prolonged irradiation the resulting photolytic products of TES–ethanol adducts are also able to emit electrons. The capability of the hormones: 17βE2, PRG and TES to eject electrons and the resulting metabolites, some of which can induce cancer, is discussed.

Reactivity between Biphenyl and Precursor of Solvated Electrons in Tetrahydrofuran Measured by Picosecond Pulse Radiolysis in Near-Ultraviolet, Visible, and Infrared

The initial decrease of solvated electrons in tetrahydrofuran (THF) upon addition of biphenyl was investigated by picosecond pulse radiolysis. Transient absorption spectra derived from the biphenyl radical anion (centered at 408 and 655 nm) and solvated electrons of THF (infrared) were successfully measured in the wavelength region from 400 to 900 nm by the extension of a femtosecond continuum probe light to near-ultraviolet using a second harmonic generation of Ti:sapphire laser and a CaF2 plate. From the analysis of kinetic traces at 1300 nm considering the overlap of primary solvated electrons and partial biphenyl radical anion, C37, which is defined by the solute concentration to reduce the initial yield of solvated electrons to 1/e, was found to be 87 +/- 3 mM. The rate constant of solvated electrons with biphenyl was determined as 5.8 +/- 0.3 x 10(10) M(-1) s(-1). We demonstrate that the kinetic traces at both 408 nm mainly due to biphenyl radical anion and 1300 nm mainly due to solvated electrons are reproduced with high accuracy and consistency by a simple kinetic analysis. Much higher concentrations of biphenyl (up to 2 M) were examined, showing further increase of the initial yield of biphenyl radical anion accompanying a fast decay component. This observation is discussed in terms of geminate ion recombination, scavenging, delayed geminate ion recombination, and direct ionization of biphenyl at high concentration.

One-photon photodetachment of I− in glycerol: Spectra and yield of solvated electrons in the temperature range 329⩽T⩽536K

Solvated electrons in glycerol were generated via a resonant one-photon photodetachment of the charge-transfer-to-solvent (CTTS) band of I- in glycerol (Gl) after irradiation with a 248 nm excimer laser. Optical absorption spectra of solvated electrons (esolv-) in Gl were recorded as a function of temperature (381<or=T<or=505 K). The observed redshift of the absorption maximum, homegamax, yields a temperature coefficient d(homegamax)/dT=-(2.67+/-0.07)x10(-3) eV K-1. For solutions with a concentration c(I-) approximately 10(-3)M, the absorbance of esolv- at homegamax increases by a factor of about 65 when the temperature is raised from 329 to 536 K. This effect can be partially explained by a temperature-dependent redshift of the CTTS spectrum of I- in Gl with respect to the laser wavelength. The main contribution to the increasing yield of esolv- is determined by diffusion controlled escape dynamics of the electron in the contact pair (I:e-)solv which is formed very fast during the detachment process. At room temperature no absorption of esolv- (absorbance<1.0x10(-3)) could be observed which is probably a result of an extremely small self-diffusion coefficient of Gl (a factor of 1250 lower than that of water at 298 K). The results are compared with a previous study of I- in ethylene glycol.

Evidence for laser-induced formation of solvated electrons in room temperature ionic liquids

The photolytic generation of solvated electrons was observed for the first time in two room temperature ionic liquids (RTILs), trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide (IL) and 1-butyl-1-methyl-pyrrolidinium bis(trifluoromethylsulfonyl)imide (IL). A 70 fs UV-pulse was used to excite the RTILs, while the transient response was monitored in the visible and near-infrared spectral regions. Immediately after excitation, a pulse duration limited rise of the induced absorption indicated the formation of solvated electrons suggesting the existence of pre-formed traps in RTILs. A broad transient absorption spectrum with a full width at half maximum of about 0.9 eV, typical for solvated electrons, was reconstructed from the transient profiles. Wavelength-independent relaxation dynamics at longer delay times suggest a lifetime of solvated electrons in the ns regime in agreement with results from pulse radiolysis studies. Adding 1,1-dimethylpyrrolidinium iodide to IL led to an increase of the UV absorbance and consequently, to an increase of the yield of solvated electrons. Furthermore, this solute is an efficient electron scavenger causing the transients to decay within about 40 ps.

Radiolysis of silver ion solutions in ethylene glycol: solvated electron and radical scavenging yields

The solvated electron yield in neat ethylene glycol (1,2-ethanediol), measured using pulse radiolysis, is G ( e solv - ) 10 ns =(1.7±0.2)×10 −7 mol J −1. The rate constant of the reaction of solvated electrons with silver cations is k ( e solv - + Ag + ) =(2.8±0.1)×10 9 dm 3 mol −1 s −1 and the absorption band maximum of Ag 0 is at 350 nm. The surface plasmon band of the silver clusters appears slowly at around 400 nm with a coalescence cascade rate constant of 2×10 6 dm 3 mol −1 s −1. The free silver ions do not scavenge ethylene glycol radicals. In contrast, the γ-radiolysis reduction yield of Ag + into clusters is dose-dependent, changing from G i(Ag n )=(2.5±0.5)×10 −7 mol J −1 at low dose to G max(Ag n )=(7.5±0.5)×10 −7 mol J −1 at higher doses, when clusters accumulate. Silver cations adsorbed on clusters are able to scavenge the ethylene glycol radicals, which also contribute to their reduction for a part of G rad=(5.8±0.5)×10 −7 mol J −1. Considering the different ways the reducing radicals can be produced, it is concluded that they originate from the electron–cation recombination and from the cation–ethylene glycol reaction, but that the dissociation of excited states is a negligible path. The formation mechanisms of the radicals and the rate constants in ethylene glycol are compared with those in water and methanol.

Specifics of Interaction of Acetone Molecules with Quasi-free Electrons: Analysis of Positron Annihilation Characteristics in Aqueous and Alcoholic Acetone Solutions

The yields of formation of radiolytic hydrogen (H2) and orthopositronium (o-Ps) in aqueous and alcoholic acetone solutions were experimentally determined. A decrease in the o-Ps yield with an increase in the acetone concentration is much weaker than the decline in the yield of solvated electrons (e–s) under picosecond pulse radiolysis conditions. In contrast, the decrease in the o-Ps yield is minimal in higher alcohols where the inhibiting action of acetone e–s is most pronounced. These findings seem to contradict the conventional concepts of Ps formation via the intratrack reaction of positron recombination with a track electron (e–), which competes with the reaction of e– scavenging by dissolved acetone molecules. This contradiction can be eliminated, assuming that the scavenging of e– by acetone begins from the formation of the weakly bound transient state (CH3)2CO···e– capable of donating e– to a positron. This opens up an additional pathway for the formation of the Ps atom.

Spur Decay Kinetics of the Solvated Electron in Heavy Water Radiolysis

Spur decay kinetics of the hydrated electron following picosecond pulse radiolysis of heavy water have been measured using a time-correlated absorption spectroscopy (TCAS) technique. The TCAS data collected for the first 40 ns of the decay was matched up with single-shot transient digitizer data out to microsecond time scales. The decay shape in heavy water looks exactly like the decay in light water except in the first 10 ns. The “time zero” solvated electron yield in heavy water radiolysis must be approximately 7% larger than in light water, to match the best available scavenger product measurements. We propose an explanation in terms of the larger distances traveled by electrons in heavy water prior to localization. The implication is that presolvated H2O+ “holes” are very efficient scavengers for the presolvated conduction band electrons.

The spectra and the relative yield of solvated electrons produced by resonant photodetachment of iodide anion in ethylene glycol in the temperature range 296⩽T⩽453 K

We have produced solvated electrons (esolv−) in ethylene glycol (EG) by irradiation of a 248 nm laser pulse in the charge-transfer-to-solvent (CTTS) band of I− (resonant photodetachment). We report on the optical absorption spectra of esolv− as a function of temperature. A red-shift of the position of the absorption maximum, Δℏωmax≈−0.4 eV, corresponding to d(ℏωmax)/dT=−(2.49±0.07)×10−3 eV K−1 in the temperature range 296⩽T⩽453 K is reported. The observed absorbance of esolv− at ℏωmax increases by a factor of about 60 when the temperature is increased from 296 to 453 K. This effect can be explained only partially by the favorable red-shift of the CTTS spectrum of I− with respect to the laser wavelength by increasing the temperature. The self diffusion coefficient in EG is by a factor of 25 lower than in water at 298 K and increases strongly with temperature. It is concluded that a reaction step with a diffusion controlled escape probability for the electron determines the yield of esolv−. The results are, therefore, analyzed according to a simple kinetic model proposed by Staib and Borgis [J. Chem. Phys. 104, 9027 (1996)].

Photoionization Yield vs Energy in H2O and D2O

A simple conductivity jump method was used to measure the escaped solvated electron yield following two-photon excitation of water with Raman-shifted light from an amplified mode-locked Nd:YAG laser. Between 7.8 and 9.3 eV, the quantum efficiency for the escape yields changes from 1.9% to 22%, with an almost exponential dependence on the excitation energy. Quantum efficiency in D2O is smaller and resembles the H2O behavior at 0.35 eV lower energy. The quantum yield measured for one-photon excitation near the water absorption edge at 6.4 eV is a surprisingly large 1.3%. We propose that the mechanism for low energy photoionizaton of water is best described as a dissociative proton-coupled electron transfer to a preexisting trap.

Spur Decay of the Solvated Electron in Picosecond Radiolysis Measured with Time-Correlated Absorption Spectroscopy

Spur decay kinetics of the hydrated electron following picosecond pulse radiolysis of water have been measured using a time-correlated transient absorption technique with an asynchronous mode-locked laser. The 11 ns time window afforded by this signal-averaging technique is ideal to match up with more conventional transient absorption measurements taken to microsecond time scales. The precise data recorded in this study require a revision downward of the “time zero” solvated electron yield to approximately 4.0 per 100 eV of energy absorbed, to match the best available scavenger product measurements.

Effect of ion pairing on electron scavenging and solvated electron yield enhancement in methanol: a comparison between pulse radiolysis and positron lifetime spectroscopic data

The influence of ion pairing on electron scavenging in nitrate solutions and the effect of amines on the enhancement of the electron yield, two particular processes previously observed in positron annihilation (PA) studies on positronium (Ps) formation in methanol, are examined by using picosecond pulse radiolysis (PR). These studies show that the scavenging of the precursors of the solvated electron (e{sub sol}{sup {minus}}) does not depend on ion pairing while confirming previous results that ion pairing strongly affects the reaction of e{sub sol}{sup {minus}} with LiNO{sub 3} and NH{sub 4}NO{sub 3}. The results from positronium annihilation studies agree with the precursor scavenging results for NO{sub 3}{sup {minus}} and NH{sub 4}NO{sub 3}; however, LiNO{sub 3} is a weaker electron scavenger. No increase in the initial e{sub sol}{sup {minus}} yield is detected in PR in the presence of amines, whereas the Ps yield is significantly increased. These apparent differences can be explained if one considers the importance of the trap depth for the electron, whether it has been captured by a solute (LiNO{sub 3}) or it has recombined with the positive ion (amines). In either case, in PR, the electron is lost for the free e{sub sol}{sup {minus}} yield. In PA onmore » the contrary, if both types of traps are shallow enough, the electron can still be picked off by the positron to form Ps.« less

Ion–electron pairs in condensed polar media treated as H-like atoms

A model of radiation produced ion–electron pairs with an electron energy below about 1 eV is proposed for the description of electron moderation, self-trapping, and escape in condensed polar media. A discrete ion–electron pair is regarded as a ground-state H-like atom which interacts with the medium through polarization forces and by experiencing energy fluctuations. Slowly relaxing polarization makes electron energy decrease on the time scale of constant-charge dielectric relaxation. A strongly attracting polarization well is formed immediately upon ion pair formation owing to instantaneous polarization. Energy fluctuations can make the electron escape from the field of the ion, but not from that of the polarization well, i.e., the electron is already self-trapped when moderation and escape take place. The rate of electron moderation was found to agree with earlier estimates made by Fröhlich and Platzman. Solvated electron yields, by allowing also for initial recombination of energetically independent ion–electron pairs, were evaluated for a series of polar liquids and for ice as a function of εs2cp1/2, where εs is static relative permittivity and cp is specific heat. By making use of one common adjustable parameter for all the systems discussed, good agreement was obtained with the majority of the experimental data.

Radiolysis of liquids with high static dielectric constant: An estimate of the total ionization yield, electron thermalization distance, and contribution of heterogeneous reactions

In a previous study, we found an exponential dependence of the free-ion yield (Gfi) on the static dielectric constant (εs) for a number of irradiated liquids with εs&amp;gt;10. On the basis of this study, we develop here a simple model by which we quantitatively estimate the total ionization yield (Gtot), the most probable electron thermalization distance (b), and the yield of solvated electrons that are removed by diffusion-controlled reactions during spur expansion (Gdif). Using solvated electron yields available in the literature, we get Gtot≂6.6 mol/100 eV (value nearly independent of the nature of the liquid) and b≂29 Å at 298 K. b is found not to depend appreciably on εs which indicates that the Coulomb attractive force between the ion and secondary electron is practically inefficient before electron thermalization occurs. The evaluation of Gdif teaches us that spur reactions have a profound influence in the fate of ion pairs formed during radiolysis of liquids of high εs values.

A pulse radiolysis study of solvated electrons in tert-butanol/water solutions

Many solutes, added to water in amounts of a few mol%, cause an increase in the yield of solvated electrons (es−) measured by pulse radiolysis. A pulse radiolysis study of tert-butanol (tBuOH) in D2O has been carried out to investigate this phenomenon. Detailed measurements of the yield, measured as Gεmax(es−), and the deeay of solvated electrons were made at 6, 25, and 46 °C over the range 0–5mol% tBuOH. The maximum Gεmax(es−) occurs at about 1 mol% tBuOH, but the exact concentration depends on the temperature of the sample and the time after the pulse at which the measurement is made. Three factors are examined as contributing to the increased Gεmax(es−) in the presence of tBuOH and certain other solutes. They are (i) the change in viscosity produced by the added solute, (ii) the scavenging of OH radicals by the solute, thereby reducing the reaction of OH with es− and (iii) the possibility that the addition of the solute leads to an increase in the thermalization distance of the secondary electrons. It is concluded that effects (i) and (ii) are sufficient to explain the existing experimental data.

Yields of Solvated Electrons at 30 Picoseconds in Water and Alcohols

Abstract Direct measurements of the yield of hydrated electrons in aqueous solutions and solvated electrons in alcohols were carried out using a stroboscopic picosecond pulse radiolysis system. The yield of solvated electrons was obtained by simultaneous consideration of the pulse shape and radiation doses. The yield at 30 ps after irradiation, G(eaq−)30ps, was determined to be 4.8±0.3 products per 100 eV as compared to the G(eaq−)100ns of 2.7. Experimental values, including the present ones, are higher by 0.3 than the theoretical ones calculated using the spur diffusion model in the time period from 3×10−11 to 10−8 s. Nevertheless, both results show a quite similar time dependence, i.e., fast decay of hydrated electrons in spur reactions. The G-values of solvated electrons at 30 ps were also determined in alcohols. The G-value of solvated electron is 3.4±0.3 in both methanol and ethanol, 2.0±0.3 in 1-propanol and 2.3±0.3 in ethylene glycol.