Radiation-induced effects in lignin model compounds: a pulse and steady-state radiolysis study
Claudio ChuaquiSrinivasan RajagopalAndrás KovácsT M StepanikJohn E. MerrittI. GyörgyR. WhitehouseDon Ewing
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Fragmentation
Bond cleavage
Hydroxylation
Solvated electron
Cleavage (geology)
Many solutes, added to water in amounts of a few mol%, cause an increase in the yield of solvated electrons (e s − ) measured by pulse radiolysis. A pulse radiolysis study of tert-butanol (tBuOH) in D 2 O has been carried out to investigate this phenomenon. Detailed measurements of the yield, measured as Gε max (e s − ), and the deeay of solvated electrons were made at 6, 25, and 46 °C over the range 0–5mol% tBuOH. The maximum Gε max (e s − ) 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 Gε max (e s − ) 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 e s − 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.
Solvated electron
Thermalisation
Radiation chemistry
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Observations of the solvated electron in water and the common aliphatic alcohols have been made in the time region ∼ 20–350 psec. Molar concentrations of acid have been used to scavenge eaq− and k(eaq−+Haq+) has been measured as (1.2 ± 0.2) × 1010 liter/mole·sec for [Haq+] from 0.5 to 5.0M. The factors limiting the time response of our picosecond pulse radiolysis system are discussed. The time of formation of esol− is estimated to be less than 10 psec for all solvents studied. The yield of solvated electrons in alcohols has been measured to be approximately one-third of the yield in water at picosecond times.
Solvated electron
Picosecond
Limiting
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The decay of solvated electrons in various aqueous solutions was studied using a stroboscopic pulse radiolysis technique with a time resolution of 24 psec. High concentrations of solutes such as H2O2, acetone, CdCl2, NaNO2, and NaNO3 decreased the initial solvated electron yield, while high acid concentrations did not. Reasons for this reduction in yield are discussed, and the conclusion reached is that the scavengers must be reacting with a precursor to the solvated electron. We believe that this precursor is probably a low-energy electron which reacts prior to solvation.
Solvated electron
Picosecond
One-electron reduction
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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.
Solvated electron
Microsecond
Heavy water
Picosecond
Electron capture
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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 N 2 O. N 2 was formed with a yield G(N 2 ) = 4.4 ± 0.4. After elimination of a certain number of processes which might also lead to N 2 formation, it was concluded that this G(N 2 ) 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 N 2 remains constant whenever solutes generally known as good electron scavengers are added (H + , CH 3 COCH 3 , NO 3 − ). An interpretation of the results leads to the suggestion of the formation of a dielectron in this medium.
Solvated electron
Scavenger
Radiation chemistry
Saturation (graph theory)
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Pulse radiolysis of 10 M OH– solution between 300 and 77 K shows (i) that the maximum yield of solvated electrons is 5, 30% of which do not escape from the spurs; (ii) that this medium is rigid below 135 K, and (iii) that diffusion-controlled reactions in this medium obey the equation ln k= ln A–E/R(T– 135), values of A lying in the range 1011 to 1012M–1S–1 and E from 6·4 to 7·4 kJ mole–1.
Solvated electron
Radiation chemistry
Aqueous medium
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Solvated electron
Radiation chemistry
Liquid water
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Solvated electron
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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.
Solvated electron
Quantum yield
Radiation chemistry
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Solvated electron
Reactivity
Radiation chemistry
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