Yield Of Solvated Electrons Research Articles

The radiolysis at room temperature and 118 °C of aqueous solutions containing sodium nitrate and either sodium formate or 2-propanol

Deoxygenated sodium nitrate solutions (≤ 2.5 × 10−2 M) containing sodium formate (≤ 0.5 M) have been irradiated at room temperature and 118 °C. With formate concentrations ≤ 5 × 10−2 M, G(NO2−) increased ~25% over the temperature range. Calculations suggest part of this increase in G(NO2−) may arise from an increase in the overall solvated electron yield. With 0.5 M sodium formate solutions containing 2.5 × 10−2 M sodium nitrate, G(NO2−) rose from 3.6 at room temperature to ~14 at 118 °C, suggesting the occurrence of a chain reaction at higher formate concentrations. G(H2O2) and G(H2) were not functions of temperature for all the above solutions.The pH dependence of G(NO2−) was determined at room temperature for sodium nitrate solutions containing either sodium formate or 2-propanol. The G(NO2−) as a function of pH could only be modelled satisfactorily with rate constants from the literature in the sodium formate case.It is concluded that the solvated electron yield in irradiated aqueous solutions at elevated temperatures cannot be confidently deduced from measurements made with nitrate as an electron scavenger in the presence of formate ions or alcohols.

Partially diffusion-controlled recombination

We extend Tachiya’s method for treating totally diffusion-controlled recombination of a pair of particles to partially diffusion-controlled recombination. The differential equation satisfied by the survival probability of the pair is derived, and solved for several cases of practical interest. Recent experiments on the solvated electron yield in liquid ammonia are analyzed by use of the present theory. It is confirmed that the rather high yield of solvated electrons in irratiated liquid ammonia is due to the slowness of the recombination reaction e−s+NH+4.

Photoejection of electrons from flavins in polar media.

Riboflavin and 12 of its derivatives have been shown to form solvated electrons under ultraviolet irradiation (253.7 nanometers) in various water-methanol solvent mixtures. The highest quantum yield of solvated electrons (about 0.03) was obtained for flavins containing tyrosine on a side chain in the isoalloxazine N-3 or N-10 position. The splitting of hydrogen atoms from excited flavin molecules was also observed. From the results presented here, it can be determined that the semiquinone transients are formed not only by way of the flavin triplet, as usually suggested, but also by the attack of the electrons and hydrogen atoms on flavin molecules in the ground state. This is important, because the flavin radicals remaining after the electron-ejection or hydrogen-splitting processes must also be considered in the subsequent reaction mechanisms. The electron-ejection process from electronically excited flavins has important implications in the photobiology of these compounds.

The effect of temperature on the optical spectra and the yields of solvated electrons and ion-pairs in amines

Optical absorption spectra for the solvated electron, es−, and ion-pairs, (Na+, es−), have been observed in methylamine (MA), ethylamine (EA), and isopropylamine (IPA), at temperatures ranging from 184 to 338 K. Changes in the (Na+, es−) spectra, relative to es−, are consistent with a gradual transition in the ion-pair structure toward a more 'electron-like' entity with decreasing temperature and increasing solvent polarity. Extinction coefficients, εmax(es−) = 3.3 ± 0.2, 3.2 ± 0.5, and 3.2 ± 0.5 × 104 M−1 cm−1 in MA, EA, and IPA respectively. Corresponding values for the ion-pairs, εmax(Na+, es−) = 2.5 ± 0.2, 2.1 ± 0.2, and 1.9 ± 0.2 × 104 M−1 cm−1.In EA and IPA, the yield [Formula: see text] (molecules/100 eV) shows a marked solute concentration dependence. This is consistent with an empirical scavenging model from which the escaped solvated G(es−)esc and spur G(es−)spur electrons are estimated as G(es−)esc = 0.5 and 0.4, G(es−)spur = 1.8 and 1.4, giving G(es−)total = 2.3 and 1.8 in EA and IPA, respectively. In MA, [Formula: see text] = G(es−)esc = 2.25 ± 0.2, independent of solute concentration.

Yield and properties of solvated electrons created by the γ radiolysis of hexamethylphosphorotriamide

According to various authors, the value of the yield of the solvated electron in the pulse radiolysis of hexamethylphosphorotriamide (HMPT) varies from 1.2 to 2.4 and increases to 4.2 or 3.1 in the presence of NaBr. We exposed this compound to γ rays after purification and saturation with N2O. N2 was formed with a yield G(N2) = 4.4 ± 0.4. After elimination of a certain number of processes which might also lead to N2 formation, it was concluded that this G(N2) corresponds to the total yield of electrons. This value was confirmed by measuring G(Br−) obtained by radiolysis of HMPT with p-bromophenol as a scavenger. The yield of N2 remains constant whenever solutes generally known as good electron scavengers are added (H+, CH3COCH3, NO3−). An interpretation of the results leads to the suggestion of the formation of a dielectron in this medium.

Effects of very high dose-rates on solvated electron yields (Extended Abstract)

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Optical spectra and yields of solvated electrons and metal-electron species in alkali metal systems

The effect of solvent on the optical spectra of solvated electrons, e–s, cation-electron aggregates, (M+, e–s), and alkali metal anions, M–, is discussed for a variety of alkali metal systems. With increasing solvent polarity the optical band maxima shift toward the blue with the solvent dependence decreasing significantly in the order (M+, e–s) > e–s > M–. The relative differences are interpreted in terms of ion-pairing and cation solvation. In ethylamine + ammonia mixtures only the e–s band exhibits a pronounced dependence on solvent composition consistent with preferential solvation by NH3 molecules.Initial yields of e–s measured by pulse radiolysis in methylamine (MA), ethylamine (EA) and isopropylamine (IPA) correspond to G(e–s)∼ 2, whereas the fraction of electrons escaping the spur decreases markedly in the order MA > EA > IPA. The results indicate that the decay processes for e–s in MA (and NH3) are slow compared with the rate of diffusion. In EA and IPA the decay is markedly temperature dependent and at temperatures approaching the freezing point is comparable with that in MA. This leads to an escaped yield approaching that observed for MA.

Primary trapping and solvated electron yields. Part 1. Recombination kinetics. Part 2. Correlation between G-value and neutralization efficiency

The isothermal decay of luminescence emitted in frozen hydrocarbons as a result of the recombination of trapped electrons with aromatic solute cations has been studied in relation to theoretical models for the primary processes of radiolysis. The kinetics were determined on a time scale extending from ∼20 to 800 ns, with radiations of different LET.In polar liquids the influence of physical as well as chemical properties of the solvent on the yield G(e–solv) at a given time (t= 3 ns) has been investigated: in particular, evidence was found of the existence of a correlation between the survival probability of e–solv and the efficiency factor of the e–solv-cation recombination, which had so far been assumed to be limited only by diffusion.

Pulse radiolytic formation of solvated electrons in hydrazine

The spectrum and yield of solvated electrons in anhydrous hydrazine have been investigated by pulse radiolysis. At room temperature the optical absorption band has a maximum at 1.22 eV (1015 nm) with a molar extinction coefficient of 2.2 ± 0.1 × 104 M−1 cm−1 and a temperature coefficient of 1.5 × 10−3 eV deg−1 from 7–45 °C. The oscillator strength is estimated to be 0.6. The optical transition energy is in reasonable agreement with an empirical correlation of solvent properties proposed by Freeman provided that only the polarisability of the nitrogen lone-pair electrons contribute to Emax. Comparisons are made with liquid amides which also have lone-pair polarisable groups and with water and liquid ammonia which have physical properties very similar to hydrazine. Electron yields increase from [Formula: see text] in pure hydrazine to 2.65 + 0.15 in basic solutions containing ≥0.1 M sodium hydrazide.

Effect of temperature on the solvated electron in 1-propanol

The technique of pulse radiolysis has been used to study the effect of temperature on the solvated electron in 1-propanol. The spectrum of the solvated electron has been measured in the range 140–298 K. The wavelength at maximum absorption, λ max, decreases with decreasing temperature (corresponding to an increase in the energy, E max) but the spectral width at half height, ΔE 1 2 , changes little with temperature. At temperatures above ≈180 K, the formation of the solvated electron is complete at the end of the pulse and its spectrum shows no change in shape with time. Below ≈170 K, the absorption spectrum is time-dependent in both liquid and glassy phases, the changes being attributed to the solvation process. The reaction(s) leading to solvated electron formation following the pulse show an activation energy of 22±2 kJ mol − and the solvated electron decays with an activation energy of 20±2 kJ mol −1. The yield of solvated electrons decreases continuously with decreasing temperature in the range 298-77 K and, at all temperatures studied, is less than the total ionization yield measured by scavenging techniques.

Effect of temperature on the yield of solvated electrons in liquid ethanol

The decay of the solvated electron and the relative yields of free and geminate solvated electrons have been measured in ethanol in the range 150–290 °K. The estimated absolute yields at low temperature agree well with sub-nanosecond values at room temperature, however the yield of solvated electrons appears to be substantially less than the total ionization yield. (AIP)

Reactions of solvated electrons with solutes at high concentrations. A laser photolysis and pulse radiolysis study

Solvated electrons were produced in several liquids by laser photoionization of aromatic solutes, and by pulse radiolysis. The yields of solvated electrons were decreased by high concentrations (0.1–1.0M) of phenol, benzene, and ethyl acetate; the effectiveness of the solutes in reducing the e−s yields was greater in the photolysis experiments than in the corresponding pulse radiolysis experiments. The data were, however, identical with light of wavelength 3471 or 2650 Å, from ruby and neodymium lasers, respectively. The data are used to discuss several theories. Solvated electrons in alcohols were photobleached with red light (λ=6942 Å) giving H atoms. The quantum yield for the process was found to be low.

ChemInform Abstract: SOLVATED ELECTRON YIELDS IN PULSE‐IRRADIATED LIQUID 1‐PROPANOL

The optical absorption spectrum of the solvated electron in 1‐propanol and its decay at various temperatures following a pulse of electrons have been studied, and the relative yields of geminate and free solvated electrons have been obtained. From these, the absolute yields have been estimated over the temperature range 150–298 K.

Solvated electron yields in pulse-irradiated liquid 1-propanol

The optical absorption spectrum of the solvated electron in 1-propanol and its decay at various temperatures following a pulse of electrons have been studied, and the relative yields of geminate and free solvated electrons have been obtained. From these, the absolute yields have been estimated over the temperature range 150–298 K.

Yield of Solvated Electrons in the Aliphatic Alcohols at Picosecond Times

Yield of Solvated Electrons in the Aliphatic Alcohols at Picosecond Times

Pulse Radiolysis of Liquid Methylamine, Ethylamine, and Ammonia: The Yield of Solvated Electrons

Yields of solvated electrons, [Formula: see text], have been measured in both the pure and basic solvents using biphenyl and pyrene as electron scavengers. In pure methylamine and ethylamine [Formula: see text]and 1.84 ± 0.1, respectively. However in basic solution these yields more than double giving [Formula: see text]. In liquid NH3 and ND3 at −15 °C, [Formula: see text] and 3.6 ± 0.2, respectively. The latter yields seem independent of base and temperature from −15 to −50 °C. Comparisons with previous work are discussed.

Solvated electrons in alcohol-alkane and alcohol-amine solutions

The absorption spectrum of the solvated electron formed by pulse radiolysis of solutions of ethanol in 3-methylpentane, 2,2-dimethylbutane, and neopentane is unaffected by the presence of these alkanes above a few mole per cent of ethanol at room temperature. Above about 20 mol% solvated electron yields per unit of absorbed energy increase in the same order as the radiolytic free-ion yields of the pure alkanes. Below about 10 mol% this order is reversed and the half-time for decay of the solvated electron at constant solution composition also decreases with increasing extent of chain branching in the alkane constituent. Similarly, the solvated electron yield in dilute solutions of methanol, ethanol, and cyclohexanol in neopentane decreases with increasing hydrocarbon character of the alcohol constituent. ln ethanol- ethylenediamine solutions the amine is, to the contrary, the dominant solvating agent. These observations are discussed in the context of preferential solvation of excess electrons by microscopic aggregates of alcohol molecules and destabilization of these aggregates by alkanes and ethylenediamine. (auth)

Yield of solvated electrons in pulse radiolysis of liquid ammonia

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Spectrum, Kinetics, and Radiation Chemical Yield of Solvated Electrons in Hexamethylphosphoric Triamide

The spectrum, yield, and kinetics of solvated electrons in hexamethylphosphoric triamide were investigated by the pulse radiolysis method. The optical absorption band is in the infrared with a maximum at 2200 ± 100 nm. The molar absorptivity at this maximum is (3.2 ± 0.5) × 104 M−1 cm−1, and the oscillator strength for the transition is estimated to be f = 0.7 ± 0.2. A free ion yield of G(es−) = 2.3 + 0.4 solvated electrons/100 eV was determined from the observed yields of anthracene and pyrene radical anions formed by electron attachment.Kinetic studies provided values of the rate constants for the reaction of solvated electrons with anthracene and N2O. The decay mechanism of the solvated electrons in the absence of added solutes was found to be complex, and the half-life (in the range of 2 to 50 μs) was dependent on experimental conditions. A second transient species, absorbing at wavelengths below 500 nm, was observed but not identified. In solutions containing bromide ion the species Br2− was observed. The pulse radiolysis of stable solutions of es−, formed by dissolving sodium metal in HMPA, is also reported.

The radiolysis of binary ethanol-water mixtures

Hydrogen, nitrite, acetyldehyde, 2,3-butanediol and hydrocarbon yields produced by the radiolysis of lithium nitrate in binary ethanol-water mixtures containing respectively 5, 10 and 15 moles dm −3 of alcohol have been determined. The “free-ion” solvated electron yields support the low value of G e S − (0·9−1·2) for pure ethanol. The results also show that the “molecular” acetaldehyde yield is not formed by the dismutation of hydroxyethyl radicals.