- Electron Spin Resonance and Pulse Radiolysis Studies on the Reaction of OH* and SO4*- with Five-Membered Heterocyclic Compounds in Aqueous Solution
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The reactions of several five-membered oxygen and nitrogen heterocycles with OH* and SO4*- radicals have been investigated in aqueous solution using in-situ radiolysis and photolysis ESR, and optical and conductometric pulse radiolys
- Dogan, I.,Steenken, S.,Schulte-Frohlinde, D.,Icli, S.
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- Electron-transfer component in hydroxyl radical reactions observed by time resolved resonance raman spectroscopy
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The existence of an electron-transfer pathway in the reaction of ·OH radical with aromatic molecules in water has been established, for the first time, using time-resolved resonance Raman spectroscopy as a diagnostic tool and p-dimethoxybenzene as a model system. In the currently accepted mechanism, the cation radical is produced by ·OH addition to the ring, followed by loss of OH-. The present work demonstrates that this process competes with direct electron transfer. A generalized reaction mechanism has been proposed in terms of potential energy diagrams to explain two-step formation of the cation radical. In this reaction mechanism, the electron- transfer component and the rate of OH- elimination from the ·OH adduct both depend on the ionization potential (IP) of the molecule. The cation radical yield by electron transfer increases from 6% in p-dimethoxybenzene to 30% in p-anisidine and 85% in p-phenylenediamine. For neutral molecules with IP > 8 eV, the ·OH addition is the first step in the chemistry, and for IP 7 eV, it is the electron transfer. In the intermediate IP range, both processes occur simultaneously.
- Tripathi
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- Pulse Radiolysis Study of Concentrated Sulfuric Acid Solutions; Formation Mechanism, Yield and Reactivity of Sulfate Radicals
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In the pulse radiolysis of concentrated sulfuric acid solutions, the absorption spectrum and the molar absorption coefficient (1600 dm3 mol-1 cm-1) of the sulfate radical are unchanged up to 10 mol dm-3 H2SO4, suggesting that the sulfate radical exists in the dissociated form (SO4-).Two formation processes for the sulfate radical have been directly demonstrated in sulfuric acid and hydrogensulfate solutions: a fast one completed in the duration of the electron pulse, and a slow one occuring over a microsecond time range.For sulfate solutions only the fast formation process is observed.In sulfuric acid solutions the slow formation process is OH + HSO4- -> H2O + SO4- (4.7 x 105 dm3 mol-1 s-1) and OH + H2SO4 -> HSO4 + H2O -> SO4- + H3O+ (1,4 x 107 dm3 mol-1 s-1) and the fast formation process is the direct action of radiation on sulfuric acid with a G value of (2.7 +/- 0.4) x 10-2 molecule eV-1.The yields of (OH + SO4-) and H can be quantified as: G(OH + SO4-) = 2.9fw + 2.7fs and G(H) = 3.7fw + 2.7fs.The yields of SO4- have also been evaluated and the decay kinetics and reactions of the sulfate radical studied.
- Jiang, Pei-Yun,Katsumura, Yosuke,Nagaishi, Ryuji,Domae, Masahumi,Ishikawa, Kenichi,et al.
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- Temperature and ionic strength effects on some reactions involving sulfate radical [SO4-(aq)]
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Sulfate radical anion SO4- was generated by 248 nm laser flash photolysis of K2S2O8 solutions and monitored by time-resolved multipass absorbance at 454 nm. The 320-520 nm absorption spectrum of SO4- was unaffected by up to 2 M added HClO4, under the experimental conditions. Three reactions were investigated: (a) SO4- + SO4- → S2O82-, (b) SO4- + H2O → HSO4- + OH, and (c) SO4- + S2O82- → products. Rate constant kc was too slow to be measured, and only an upper limit was determined: kc ≤ 104 M-1 s-1. Arrhenius parameters were determined at low ionic strength over the range 11.8-74.4°C: 2ka/∈ = (4.8 ± 2.0) × 105 exp(-1.7 ± 1.1 kJ mol-1/RT) cm s-1 and kb = (4.7 ± 0.1) × 103 exp(-15.5 ± 0.6 kJ mol-1/RT) M-1 s-1, where ∈ is the SO4- absorption coefficient at 454 nm. At 296 K, the values are in good agreement with literature values: 2ka/∈ = (2.5 ± 0.2) × 105 cm s-1 and kb[H2O] = 440 ± 50 s-1. Rate constants ka and kb were found to increase strongly and nonlinearly with increasing ionic strength (added NaClO4) or acidity (added HClO4). Ion-pair formation provides a possible explanation, and a quantitative empirical model is presented for conditions with [Na+] ≤ 1.6 M and [H+] ≤ 3 M. Using the ion-pair model, estimated ionization equilibrium constants are obtained for the H+SO4- and the Na+SO4- radical ion pairs.
- Bao, Zhen-Chuan,Barker, John R.
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- Generation and Reactions of the Chlorine Atom in Aqueous Solution
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The chlorine atom (Cl.) has been generated in aqueous solution by reaction of Cl- with SO4.- and H2PO4., obtained by metal-catalysed decomposition of the appropriate peroxides.E.s.r. experiments in conjuction with a fast-flow method establish that Cl. is highly reactive, readly undergoing rapid addition, hydrogen-abstraction and electron-transfer reactions (k = 108-109 dm3 mol-1 s-1).The factors which influence the observed selectivity (energetics and polar effects) are discussed.
- Gilbert, Bruce C.,Stell, Jonathan K.,Peet, Wendy J.,Radford, Karen J.
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- The formation of SO5- by gas phase ion-molecule reactions
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A flow tube apparatus used to investigate the formation of SO5- ions by gas phase ion-molecule reactions.The reactions studied in an N2 buffer gas at 2.5 hPa pressure and room temperature (298 K) included SO2 and O2 reactions with O2-, O3-, CO3-, SO2-, and SO3- as well as their hydrates.Reaction rate constants were measured and the major product channels were identified for most reactions.The free energy changes for the hydration reactions of SO3-, SO4-, and SO5- were derived from equilibrium constant measurements.The present investigations clearly show that SO5- ions are formed in the gas phase by the association of O2 to SO3- and by the switching reaction of SO3-H2O with O2.An effective binary rate constant of 2.0*10-12 cm3 s-1 was measured for the association reaction at 2.5 hPa N2 and the rate constant of the switching reaction was 5.0*10-11 cm3 s-1.Also the reaction of O3-H2O with SO2 probably yields SO5- by a switching process having a rate constant of 1.8*10-9 cm3 s-1.The heat of formation of SO5- was estimated to be less than -715 kJ/mol.The present results have implications to the negative ion chemistry of the atmosphere and are important for measurements of atmospheric SO2 concentrations by chemical ionization mass spectrometry.
- Moehler, O.,Reiner, T.,Arnold, F.
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- Transient intermediates in the laser flash photolysis of ketoprofen in aqueous solutions: Unusual photochemistry for the benzophenone chromophore
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The transient intermediates the nanosecond laser flash photolysis of ketoprofen, an arylpropionic acid, show the formation of a carbanion in aqueous solutions at pH 7.1. This carbanion incorporates spectroscopic properties from both a ketyl radical anion and a benzylic radical. The ketoprofen carboxylate undergoes biphotonic photoionization, a process that contributes less than 10% to its photodecomposition- and leads to a benzylic-type radical after decarboxylation with a rate constant ≤1 x 107 s-1. On the other hand, the carbanion forms monophotonically and the unsuccessful attempts to sensitize the formation of the ketoprofen triplet excited state in aqueous solutions suggest that the carbanion precursor is either an excited singlet state or an extremely short-lived triplet. In organic solvents of lower polarity, the excited triplet state is readily detectable.
- Martínez,Scaiano
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- Kinetics and Mechanism of the Interaction of Potassium Peroxydisulfate and 18-Crown-6 in Aqueous Media
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A kinetic investigation of the interaction of potassium peroxydisulfate with the crown ether 18-crown-6 in basic aqueous media has shown that the crown ether has a tremendous accelerating effect upon the rate of disappearance of peroxydisulfate.This acceleration is due in part to a radical chain mechanism in which crown is oxidized, and which is similar to that observed in the presence of simple ethers.However, an additional crown effect is observed which is explicable in terms of a Coulombic attraction between a cation-complexed crown radical and the peroxydisulfate dianion.
- Rasmussen, Jerald K.,Heilmann, Steven M.,Toren, Paul E.,Pocius, Alphonsus V.,Kotnour, Thomas A.
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- A kinetic study of the reactions of sulfate radicals at the silica nanoparticle - Water interface
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Sulfate radicals, SO4.-, were generated using flash photolysis of aqueous S2O82- solutions and the reactions of the inorganic radicals with the surface of suspended silica nanoparticles (NP) investigated. In the presence of colloidal silica no absorption traces due to SO4.- radicals are observed at 100 ??s after the flash of light. However, two transient species with absorption maxima around 320 and 600 nm are formed. A kinetic analysis of the experimental results indicate that SO4.- radicals are adsorbed on the NP surface, leading to the formation of an adduct, with ??max a?? 320 nm (?μ a?? 7000 cm-1 M-1), and showing similar reactivity to that observed for the sulfate radical in aqueous solutions. The NP - sulfate radical adducts react with adsorbed water, and with single and geminal SiO- sites with reaction rate constants of 1.5 ?? 1014 ?? e-(58?±12)kJ/mol)RT s-1, 3 ?? e-(2?±17)kJ/mol/RT s-1 and 11 ?? e-(46?±13)kJ/mol/RT s-1, respectively. Two different SiO. surface defects, showing similar spectra (??max a?? 600 nm) but different reactivities, are formed from the reaction of NP - sulfate radicals and deprotonated geminal and single silanols.
- Caregnato, Paula,Mora, Veroì?nica C.,Le Roux, Galo Carrillo,Maì?rtire, Daniel O.,Gonzalez, Moì?nica C.
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- Reaction rate constants for O2-(H2O)n ions n=0 to 4, with O3, NO, SO2, and CO2
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Reaction rate constants for O2-(H2O)n ions with n=0 to 4 have been measured in a variable temperature flowing afterglow apparatus with a novel ion source configuration.The ios have been reacted with O3, NO, SO2, and CO2.The reaction with O3 is charge-transfer to produce O3- with simultaneous transfer of water ligands.The reactions with NO and SO2 are ligand switching reactions in which NO or SO2 displaces one or more water molecules clustered to O2- leaving NO3- and SO4- as core ions.In these cases, the reaction rate constants are not decreased measurably by an increase in n.CO2 rapidly displaces H2O in reaction with O2-(H2O) but does not react with O2-(H2O)3,4.Isotopically labelled O2- ions were used to elucidate several reaction mechanisms.The rapid destruction of O2-(H2O)4 ions by O3, NO, and SO2 insure that O2-(H2O)n ions cannot be dominant small air ions in the earth's lower atmosphere.
- Fahey, D. W.,Boehringer, H.,Fehsenfeld, F. C.,Ferguson, E. E.
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- Photoelectron spectroscopy and theoretical calculations of so4- and HSO4-: Confirmation of high electron affinities of so4 and HSO4
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We present a combined photoelectron spectroscopic and theoretical study of SO4- and HSO4- and their corresponding neutral species in the gas phase. We measured very high electron affinities for SO4 and HSO4, which are 5.10(0.10) and 4.75(0.10) eV, respectively. Theoretical calculations of the neutral and anionic species using both density functional and ab initio molecular orbital theory confirm the high electron affinities of the two species. The theoretically predicted vertical and adiabatic detachment energies are in good agreement with the experimental measurements. We find that both SO4- and SO4 have C2v symmetry, whereas both HSO4- and HSO4 have Cs symmetry. We predict significant geometry changes between the equilibrium geometries of the anion species and the neutral speeds for both systems that are consistent with the broad nature of the measured photoelectron spectra.
- Wang, Xue-Bin,Nicholas, John B.,Wang, Lai-Sheng
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- Reactivity and role of SO5?- radical in aqueous medium chain oxidation of sulfite to sulfate and atmospheric sulfuric acid generation
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This study reevaluates the role of peroxymonosulfate anion radical (-O3SOO? or SO5?-) intermediate during radical-induced chain oxidation of HSO3-/SO32- in oxygenated aqueous solution. The SO5?- radical absorption band in the UV is weak: ε = 1065 ± 80 M-1 cm-1 at λmax (260-265 nm). The SO5?- radical takes part in two radical-radical and four radical-solute reactions, partially producing the other chain carrier, the SO4?- radical, in either case. In this study, employing the pulse-radiolysis technique but adopting a new approach, these two types of reactions of the SO5?- radical have been separately quantified (at room temperature). For example, over pH 3.5-12, the branching ratio of (SO5?- + SO5?-) reactions giving rise to either the SO4?- radical or S2O82- is found to remain ~1. The respective reaction rate constants for I → 0 are (2.2 ± 0.3) and (2.1 ± 0.3) × 108 M-1 s-1. The (SO5?- + HSO3-) reactions in acid pH follow two paths, forming the SO4?- radical in one and regenerating the SO3?- radical in the other, with respective rates of ca. (6.0 ± 0.4) and (3.0 ± 0.3) × 107 M-1 s-1. In alkaline pH (for SO5?- + SO32- reactions), the rates for similar reactions are ca. (5.6 ± 0.6) and (1.0 ± 0.1) × 108 M-1 s-1. From only these results, the earlier prediction of chain length reaching a few thousands could be supported in simulation studies (Bigelow, S. L. Z. Phys. Chem. 1898, 28, 493. Young, S. W. J. Am. Chem. Soc. 1902, 24, 297. Titoff, A. Z. Phys. Chem. 1903, 45, 641. Ba?ckstro?m, H. L. J. J. Am. Chem. Soc. 1927, 49, 1460. Alyea, H. N.; Ba?ckstro?m, H. L. J. J. Am. Chem. Soc. 1929, 51, 90). To explore the feasibility of controlling S(IV) chain oxidation to sulfuric acid in liquid hydrometeors, the effect of radical scavenging on each SOx?- radical (x = 3, 4, 5) was simulated. The results show that for the SO5?- radical a scavenger reactivity of ~100 s-1 may be enough to reduce the chain length by >98%. However, in the case SO4?- radical scavenging under similar conditions, only ~75-80% reduction in acid production was observed. These results suggest a fresh modeling of sulfuric acid generation in atmospheric liquid hydrometeors.
- Das, Tomi Nath
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- Reaction of sulphate radical anion SO4?- with cyanuric acid: A potential reaction for its degradation?
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A novel reaction between sulfate radical anion (SO4?-) and cyanuric acid (CA), a non-degradable end product of the oxidative degradation of the triazine based herbicide, atrazine, is presented using laser flash photolysis and steady state radiolysis techniques at pH 5. A second order rate constant of 1.9 × 107 dm3 mol-1 s-11 has been determined and the transient intermediate (λmax = 330 nm) is assigned to a radical cation of CA (CA?+). The degradation profile indicated that about 76% of CA have been decomposed after an absorbed γ-radiation dose of 18 kGy. It is therefore proposed that the reaction of SO4?- could be utilised for the degradation of CA in aqueous medium which is normally stable to any Advanced Oxidation Processes.
- Manoj,Varghese,Manoj,Aravindakumar
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- Aspects of the Oxidation of Naphthazarin as studied by Pulse Radiolysis
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The spectroscopic characteristics and kinetic parameters associated with the intermediates formed on reaction of naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) with the oxidising radicals OH., O.-, N3., Br.-.SO
- Mukherjee, Tulsi,Land, Edward J.,Swallow, A. John,Bruce, J. Malcolm,Beaumont, Paul C.,Parsons, Barry J.
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- Kinetic study of the reactions of chlorine atoms and Cl2·- radical anions in aqueous : Solutions. 1. Reaction with benzene
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The photolysis of NaS2O8 aqueous solutions containing Cl- ions is a clean technique for kinetic studies of the species Cl./Cl2.- in the presence and absence of added aromatic substrates. Laser and conventional flash-photolysis methods were used to study the aqueous phase reactions of chlorine atoms and Cl2.- (340 nm) radical ions in the presence and absence of benzene. A mechanism that considers the decay of Cl2.- in aqueous solutions with chloride ion concentrations from 1 x 10-4 to 0.6 M, total radical (Cl. + Cl2.-) concentrations at (0.1-1.5) x 10-5 M, and 2.5-3 pH was proposed. Kinetic computer simulations supported interpretation of the experimental data. The rate constants 6 x 109/M-sec ≤ k ≤ 1.2 x 1010/M-sec and 5/M-sec were determined for the reactions of Cl. and Cl2.-, respectively, in the aqueous phase. The organic radicals produced from these reactions showed an absorption band with maximum at 300 nm that was assigned to a Cl-cyclohexadienyl radical (Cl-CHD). The kinetic analysis of the traces supported a reversible reaction between Cl-CHD and O2. A reaction mechanism leading to the formation of chlorobenzene was proposed.
- Martire,Bertolotti,Braun,Gonzalez,Alegre,Gerones,Rosso
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p. 3117 - 3125
(2007/10/03)
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- Kinetics of retardation in persulphate-Fe3+-bisulphite initiated polymerization of acrylamide
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The kinetics of persulphate-Fe3+-bisulphite initiated polymerization has been studied at 30±0.2°C in oxygen atmosphere. It has been found that the polymerization kinetics is significantly altered by Fe3+ concentration. At lower concentration (2.0 × 10-4 mol dm-3) of Fe3+ the rate of polymerization follows the rate equation Rp ∝ , [monomer] [S2O82-] while at higher concentration (8.0 × 10-4 mol dm-3) the rate equation becomes Rp ∝ [M][HSO3-]. Besides affecting the polymerization kinetics Fe3+ also decreases the molecular weight of the resulting polymers. The effects of added salts and temperature on the polymerization process have also been investigated and energy of activation is calcualted to be 42.6 kJ mol-1. Retarding effect of various aliphatic alcohols, nitro compounds and nitrophenols has been studied in terms of retardation constants.
- Bajpai,Sharma
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p. 1091 - 1096
(2007/10/03)
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- Kinetics and mechanism of decomposition of persulfates in aqueous solutions of an emulsifier in the presence of hydroquinone and benzoquinone
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A kinetic method has been used to study the influence of hydroquinone and 1,4-benzoquinone on the decomposition of persulfate in aqueous solutions in the presence of components of an emulsion polymerization system consisting of an emulsifier and monomers. It has been established that the acceleration of persulfate decomposition with increasing concentration of emulsifier in the presence of hydroquinone and benzoquinone is related to a direction reaction of persulfate with a substituted hydroquinone that is obtained by the interaction of emulsifier radicals with benzoquinone. Kinetic orders of the persulfate decomposition reaction with respect to all components of the system have been determined. Monomers suppress the induced decomposition of persulfate and its reaction with the substituted hydroquinone.
- Kulikov,Yablokova,Aleksandrov
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p. 942 - 947
(2008/10/08)
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- Mechanisms of Peroxide Decomposition: An Electron Paramagnetic Resonance Study of the Reaction of the Peroxomonosulphate Anion (HOOSO3-) with CuI A marked Contrast in Behaviour with that of TiIII and FeII
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EPR spectroscopy has been employed in conjunction with a continuous-flow system to show that CuI (produced from the rapid reaction of CuII with TiIII) reacts rapidly with the peroxomonosulphate anion (k ca. 2 x 104 dm3 mol-1 s-1 at pH 2 and 20 deg C) to give the hydroxyl radical (HO.) which is trapped via its addition to alkenes.In contrast, FeII and TiIII react with HOOSO3- predominantly to give the sulphate radical-anion (SO4.-).It is argued that with CuI the reaction shows characteristics of an outer-sphere electron-transfer process, whereas inthe inner-sphere reaction of FeII and TiIII the reaction is facilitated by attack of the hydroxyl oxygen atom on the smaller, more highly charged metal ions. Evidence is also presented that radicals formed by the addition of both HO. and SO4.- to alkenes (.CR1R2CR3R4Y, Y = OH, OSO3-) are readily oxidized by HOOSO3- (k ca. 105 dm3 mol-1 s-1), a reaction which leads to the formation of SO4.-.
- Gilbert, Bruce C.,Stell, Jonathan K.
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p. 3261 - 3266
(2007/10/02)
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- Kinetics of the Reactions of the SO4- Radical with SO4-, S2O82-, H2O and Fe2+
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The sulphate radical anion, SO4-, is known to be a key intermediate in the aqueous aerobic oxidation of SO2 initiated by free radicals.The absorption spectrum of SO4- has been obtained following photolysis of K2S2O8 solutions at 248 nm.Kinetic spectrophotometric techniques have been employed to investigate the decay of SO4- in the presence of S2O82- and FeII.Several rate constants have been determined at 293 K: 2k(SO4- + SO4-) = (8.9+/-0.3) * 108 dm3 mol-1 s-1 (at infinite dilution), k(SO4- + S2O82-) = (6.1+/-0.6) * 105 dm3 mol-1 s-1 (at infinite dilution) and k(SO4- + H2O) = (500+/-60) s-1.The reaction of SO4- with FeII proceeds via a rapid equilibration step followed by electron transfer, which is rate-determining .Values of k1, k-1 and k2 at 293 K are (3.0+/-1.9) * 108 dm3 mol-1 s-1, (4.8+/-3.0) * 104 s-1 and (6.5+/-2.1) * 103 s-1 respectively.The implications of these results for current cloud and precipitation chemistry models are discussed.
- McElroy, W. J.,Waygood, S. J.
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p. 2557 - 2564
(2007/10/02)
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- Formation of the Radical Cation N2H6(.+) in Irradiated Hydrazinium Sulphate (N2H6(2+)SO4(2-)): an Electron Spin Resonance Study
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Exposure of at 77 K to (60)Co γ-rays gave SO4(.-) radicals and a novel species with two equivalent nitrogen nuclei and six equivalent protons, thought to be N2H6(.+) formed by electron capture; these species readily gave NH3(.+) radicals on annealing.
- Ganghi, Nader,Wyatt, Jane L.,Symons, Martyn C. R.
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p. 1424 - 1425
(2007/10/02)
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- MECHANISM OF CATALYTIC DECOMPOSITION OF HYDROGEN PEROXIDE AND PEROXODISULFATE IONS WITH COPPER(II) COMPOUNDS.
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It was demonstrated by the method of competing reactions using p-nitrosodimethyl-aniline (NDMA), ethanol, and 2-propanol as radical acceptors that upon catalytic decomposition of potassium peroxodisulfate with copper(II) compounds in basic medium sulfate ion-radicals are formed in the intermediate reaction stage. It was established using the NDMA radical acceptor that catalytic decomposition of hydrogen peroxide with copper(II) compounds in basic medium occurs without formation of hydroxyl radicals.
- Lunenok-Burmakina,Emel'yanov,Lezina,Grishchenko
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