- Measurements of the absorption line strength of hydroperoxyl radical in the ν3 band using a continuous wave quantum cascade laser
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Mid-infrared absorption spectroscopy has been applied to the detection of the hydroperoxyl (HO2) radical in pulsed laser photolysis combined with a laser absorption kinetics reactor. Transitions of the ν3 vibrational band assigned to the O-O stretch mode were probed with a thermoelectrically cooled, continuous wave mid-infrared distributed feedback quantum cascade laser (QCL). The HO2 radicals were generated with the photolysis of Cl2/CH3OH/O2 mixtures at 355 nm. The absorption cross section at each pressure was determined by three methods at 1065.203 cm-1 for the F1, 131,13 ← 141,14 transition in the ν3 band. From these values, the absolute absorption cross section at zero pressure was estimated. The relative line strengths of other absorptions in the feasible emitting frequency range of the QCL from 1061.17 to 1065.28 cm-1 were also measured, and agreed with values reproduced from the HITRAN database. The ν3 band absorption strength was estimated from the analytically obtained absolute absorption cross section and the calculated relative intensity by spectrum simulation, to be 21.4 ± 4.2 km mol-1, which shows an agreement with results of quantum chemical calculations.
- Sakamoto, Yosuke,Tonokura, Kenichi
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- Investigation of the radical product channel of the CH3OCH 2O2 + HO2 Reaction in the Gas Phase
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The reaction of CH3OCH2O2 with HO 2 has been investigated at 296 K and 700 Torr using long path FTIR spectroscopy, during photolysis of Cl2/CH3OCH 3/CH3OH/air mixtures. The branching ratio for the reaction channel forming CH3OCH2O, OH, and O2 has been determined from experiments in which OH radicals were scavenged by addition of benzene to the system, with subsequent formation of phenol used as the primary diagnostic for OH radical formation. The dependence of the phenol yield on the initial peroxy radical precursor reagent concentration ratio, [CH 3OH]0/[CH3OCH3]0, is consistent with prompt OH formation resulting mainly from the reaction of CH3OCH2O2 with HO2, such that the inferred prompt yield of OH is well-correlated with that of CH 3OCH2OOH, a well-established product of the CH 3OCH2O2 + HO2 reaction. The system was fully characterized by simulation, using a detailed chemical mechanism which included other established sources of OH in the system. This allowed a branching ratio of k2c/k2 = 0.19 ± 0.08 to be determined. The results therefore provide strong indirect evidence for the participation of the radical-forming channel of the title reaction.
- Jenkin,Hurley,Wallington
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- Linking ion and neutral chemistry in C-H bond electrophilic activation: Generation and detection of HO2. reactive radicals in the gas phase
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The flip side: Both the charged and uncharged products formed by C-H bond electrophilic activation have been experimentally detected in the gas phase. The HO2. radical is formed by a process involving the prototypical oxygen-centered radical cation O2.+ and the methane derivative CH2F2. Copyright
- Depetris, Giulia,Angelini, Giancarlo,Ursini, Ornella,Rosi, Marzio,Troiani, Anna
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- Prompt HO2 formation following the reaction of OH with aromatic compounds under atmospheric conditions
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The secondary formation of HO2 radicals following OH + aromatic hydrocarbon reactions in synthetic air under normal pressure and temperature was investigated in the absence of NO after pulsed production of OH radicals. OH and HOx (=OH + HO2) decay curves were recorded using laser-induced fluorescence after gas-expansion. The prompt HO2 yields (HO2 formed without preceding NO reactions) were determined by comparison to results obtained with CO as a reference compound. This approach was recently introduced and applied to the OH + benzene reaction and was extended here for a number of monocyclic aromatic hydrocarbons. The measured HO2 formation yields are as follows: toluene, 0.42 ± 0.11; ethylbenzene, 0.53 ± 0.10; o-xylene, 0.41 ± 0.08; m-xylene, 0.27 ± 0.06; p-xylene, 0.40 ± 0.09; 1,2,3-trimethylbenzene, 0.31 ± 0.06; 1,2,4-trimethylbenzene, 0.37 ± 0.09; 1,3,5- trimethylbenzene, 0.29 ± 0.08; hexamethylbenzene, 0.32 ± 0.08; phenol, 0.89 ± 0.29; o-cresol, 0.87 ± 0.29; 2,5-dimethylphenol, 0.72 ± 0.12; 2,4,6-trimethylphenol, 0.45 ± 0.13. For the alkylbenzenes HO2 is the proposed coproduct of phenols, epoxides, and possibly oxepins formed in secondary reactions with O2. In most product studies the only quantified coproducts were phenols whereas only a few studies reported yields of epoxides. Oxepins have not been observed so far. Together with the yields of phenols from other studies, the HO2 yields determined in this work set an upper limit to the combined yields of epoxides and oxepins that was found to be significant (≥0.3) for all investigated alkylbenzenes except m-xylene. For the hydroxybenzenes the currently proposed HO2 coproducts are dihydroxybenzenes. For phenol and o-cresol the determined HO2 yields are matching the previously reported dihydroxybenzene yields, indicating that these are the only HO 2 forming reaction channels. For 2,5-dimethylphenol and 2,4,6-trimethylphenol no complementary product studies are available.
- Nehr, Sascha,Bohn, Birger,Wahner, Andreas
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- Absolute Rate Constant of the Reaction OH+HO2->H2O+O2
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The absolute rate constant of the reaction OH+HO2->H2O+O2 was determined by using the discharge-flow resonance fluorescence technique at 299 K and 1-torr total pressure.Pseudo-first-order conditions were used with HO2 concentrations in large excess over O
- Keyser, Leon F.
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- Production of H2O radical in the Track of High-Energy Carbon Ions
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The radiation chemical yields of H2O radical produced by irradiating water with 12C ions of 37-100-MeV initial energy have been determined. these data have been combined with previous values for lower energy carbon and helium ions to obtain the differential yields over the range 2-102 eV/Angstroem.The close similarly between the yields for helium and carbon ions of the same LET suggests that the reaction volume of interest extrends somewhat beyond the track core, especially for helium.LET appears to be a useful parameter to describe the production of H2O radicals in the tracks of heavy particles.
- La Verne, Jay A.,Schuler, Robert H.
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- Track Effects in Radiation Chemistry: Production of HO2. in the Radiolysis of Water by High-LET (58)Ni Ions
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The yields of HO2. produced in the radiolysis of water by (58)Ni ions having energies up to 460 MeV have been determined.For these radiations the differential yields for HO2. production increase from 0.26 to 0.43 molecules/100 eV over an LET range of 260-520 eV/Angstroem.From these measurements a limiting yield of 0.57 molecules/100 eV is estimated for HO2. production by energy deposited in the track core at very high LETs.These studies demonstrate the feasibility of carrying out significant radiation-chemical studies with beams of particles having LETs in excess of 200 eV/Angstroem.
- La Verne, Jay A.,Schuler, Robert H.
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- Mechanistic Investigation of the HO+HO2 Reaction
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A steady-state photolysis experiment including mass-spectrometric end-product analysis was used to conduct a mechanistic investigation of the H(18)O+HO2 reaction system.The results obtained do not support the existence of a linear adduct reaction intermediate as suggested by a proposed pressure dependennce for the title reaction: HO+HO2->H2O+O2 (k1).An elaborate modeling analysis of the experiment best matches the observed product yields for values of k1 in the range 1*10-10-2*10-10 cm3 molecule-1 s-1.
- Kurylo, Michael J.,Klais, Odo,Laufer, Allan H.
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- Reaction of O2 with the hydrogen atom in water up to 350 °C
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The reaction of the H atom with O2, giving the hydroperoxyl HO2 radical, has been investigated in pressurized water up to 350 °C using pulse radiolysis and deep-UV transient absorption spectroscopy. The reaction rate behavior is highly non-Arrhenius, with near diffusion-limited behavior at room temperature, increasing to a near constant limiting value of ~5 × 1010 M-1 s -1 above 250 °C. The high-temperature rate constant is in near-perfect agreement with experimental extrapolations and ab initio calculations of the gas-phase high-pressure limiting rate. As part of the study, reaction of the OH radical with H2 has been reevaluated at 350 °C, giving a rate constant of (6.0 ± 0.5) × 108 M-1 s-1. The mechanism of the H atom reaction with the HO2 radical is also investigated and discussed.
- Janik, Ireneusz,Bartels, David M.,Marin, Timothy W.,Jonah, Charles D.
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- Track Effects in Radiation Chemistry: Production of HO2(.) within the Track Core in the Heavy-Particle Radiolysis of Water
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The radiation chemical yields of HO2(.) radicals produced by (1)H, (4)He, (7)Li, (9)Be, (11)B, (12)C, and (20)Ne ions having energies up to 35 MeV have been determined.At energies above 10 MeV the yield with protons approaches the value of 0.020 molecules/100 eV observed with fast electrons.The yield increases with increasing mass and decreasing energy of the irradiating particle and exceeds 0.2 molecules/100 eV for low-energy (9)Be, (11)B, (12)C, and (20)Ne ions.Extrapolation indicates an upper limit of 0.37 molecules/100 eV for more massive ions.We conclude that HO2(.) is produced mainly in the track core, so that HO2(.) production is a good probe of the dependence of core processes on particle characteristics.Comparison of the differencial yields observed for different particles having the same linear energy transfer (LET) shows that these yields are not strongly dependent on the irradiating particle.After correction for energy lost to ? rays, the LET dependence of the yield pertinent to the core is common to all of the particles studied, indicating that in this case the track has expanded to some extent before reaction occurs.
- LaVerne, Jay A.,Schuler, Robert H.,Burns W. G.
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- Time-resolved Study of Hydrogen Atoms in the H2-O2 System under Conditions close to Criticality
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A time-resolved study has been performed at conditions close to criticality in the H2-O2 system.Reaction was initiatd by the exciplex laser flash photolysis of O2 at 193.3 nm.H was monitored using time-resolved resonance fluorescence and showed an approximately biexponential time dependence.Near the explosion limit, the long-time behaviour is dominated by the competition between the branching and terminating H + O2 channels.Rate coefficients for these channels were inferred from this time dependence over the ranges 800 T/K 850 and 100 P/Torr 243.
- Hanning-Lee, Mark A.,Pilling, Michael J.,Warr, Jonathan F.
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- Formation of HO2 radicals from the 248 nm two-photon excitation of different aromatic hydrocarbons in the presence of O2
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The excitation energy dependence of HO2 radical formation from the 248 nm irradiation of four different aromatic hydrocarbons (benzene, toluene, o-xylene, and mesitylene) in the presence of O2 has been studied. HO2 has been monitored at 6638.20 cm-1 by cw-CRDS, and the formation of a short-lived, unidentified species, showing broad-band absorption around the HO2 absorption line, has been observed. For all four hydrocarbons, the same HO2 formation pattern has been observed: HO2 is formed immediately on our time scale after the excitation pulse, followed by a formation of more HO2 on a much longer time scale. Taking into account the absorption of the short-lived species, the yields of both types of HO2 radicals are in agreement with a formation following 2-photon absorption by the aromatic hydrocarbons. The yields do not much depend on the nature of the aromatic hydrocarbon. For practical use in past and future experiments on aromatic hydrocarbons, an empirical value is given, allowing the estimation of the total concentration of HO2 radicals formed at 40 Torr He in the presence of around [O 2] = 1 × 1017cm-3 as a function of the 248 nm excitation energy: [HO2]/[aromatic hydrocarbon] ≈ 2 × 10-6 × E2 (with E in mJ cm-2).
- Jain, Chaithanya,Morajkar, Pranay,Schoemaecker, Coralie,Fittschen, Christa
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- Superoxide: Base, Nucleophile, Radical, or Electron Transfer Reagent?
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In contrast with the reaction in dimethylformamide, dichlorocarbene is formed from the superoxide ion and chloroform in benzene.
- Purrington, Suzanne T.,Kenion, Grant B.
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- Pressure Dependence of the Rate Constant for the Reaction HO2+NO2+M-> HO2NO2+M (M=N2, O2) at 298 K
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The pressure dependence at 298 K of the rate constant for the combination reaction between HO2 and NO2 was investigated by flash photolysis kinetic absorption spectroscopy.Measurements were made at N2 and O2 pressures ranging from 25 to 600 torr and the d
- Kurylo, Michael J.,Ouellette, Philip A.
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- Laser photolysis of O3/H2 mixtures: The yield of the H + O3 -> HO2 + O reaction
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The collisional deactivation of O(21D2) by H2 and D2 was found to proceed with a rate constant 1.0 +/- 0.1 * 10-10 cm3 molecule-1 sec-1.The hydrogen atoms produced by O(21D2) + H2 -> OH + H were observed to react with the O3 source molecule with the rate coefficient 3*10-11 cm3 molecule-1 sec-1.Oxygen atoms were seen to be formed with a similar rate and approximately 40percent of the reactive encounters of H with O3, were estimated to result in the production of oxygen atoms instead of the expected OH and O2.Possible mechanisms involving collisionally induced dissociation of O3 by vibrationally excited hydroxyl radicals do not appear to account for the observed oxygen atom kinetics in this system, thus suggesting that H + O3 -> HO2 + O may indeed be a significant pathway in the reaction of hydrogen atoms with ozone.
- Force, A.P.,Wiesenfeld, J.R.
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- Noise-immune cavity-enhanced optical heterodyne detection of HO2 in the near-infrared range
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Accurate measurements of the absolute concentrations of radical species present in the atmosphere are invaluable for better understanding atmospheric processes and their impact on Earth systems. One of the most interesting species is HO2, the hydroperoxyl radical, whose atmospheric daytime levels are on the order of 10 ppt and whose observation therefore requires very sensitive detection techniques. In this work, we demonstrate the first steps toward the application of external-cavity diode-laser-based noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) to the detection of the HO2 radical in the near-infrared range. Measurements of stable species and of HO2 were made in a laboratory setting, and the possibilities of extending the sensitivity of the technique to atmospheric conditions are discussed.
- Bell, Claire L.,Van Helden, Jean-Pierre H.,Blaikie, Tom P. J.,Hancock, Gus,Van Leeuwen, Nicola J.,Peverall, Robert,Ritchie, Grant A. D.
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- Properties of chemically generated π-radical cations and molecules of (meso-phenyl-β-octaethylporphyrinato)rhenium(V) with axial molecular oxygen
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The state of existence and reactions of stable rhenium(V) complexes with β-octaethylporphin (O=Re(OPh)OEP, O=Re(Cl)OEP) and its meso-diphenyl-substituted derivatives (O=Re(Cl)5,15DPOEP) in concentrated H2SO4 at 318-348 K were studied. It was found that O=Re(Cl)5,15DPOEP undergoes slow single-electron oxidation at the aromatic ligand to give π-radical cation. The oxidation is accompanied by replacement of the axial Cl- ligand by the hydrogen sulfate ion present in excess. Full kinetic description of the intricate oxidation reaction of the complex involving atmospheric oxygen was obtained and parameters of simple reactions that constitute the intricate process were determined. In the case of O=Re(Cl)OEP and O=Re(OPh)OEP, the reaction stops after the formation of the cationic complex with axially coordinated oxygen and outer-sphere chloride ion O=Re(O2)OEP+ Cl-. The effect of the nature of axial and macrocyclic ligands in rhenium(V) porphyrins on the processes in sulfuric acid solutions of these compounds was established.
- Bichan,Tyulyaeva,Lomova
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- Kinetics of the reaction of HO2 with ozone
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Rate constants were measured for the reaction HO2 + O3 -> OH + 202(k1) using a discharge-flow system with laser magnetic resonance detection of both HO2 and OH. k1 was determined directly from the first order decay of HO2 in excess O3 when C2F3Cl was added to scavenge the OH product and prevent interference from the faster reaction OH + O3 -> HO2 + O2(k2).The ratio k2/k1 was independently determined from the steady-state / ratio obtained without C2F3Cl.Results from the scavenger method are given by k1 = (1.4+/-0.4)x10-14 exp cm3s-1 for 245 K a directly measured value of k2 = (6.5 +/- 1.0)x10-14 cm3s-1 at 300 K.These measurements are compared with other studies and some implications for stratospheric ozone chemistry are discussed.
- Zahniser, Mark S.,Howard, Carleton J.
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- Reaction of substituted iron phthalocyanines with dioxygen in acidic medium 1. Oxidation of iron 5,5′,5″,5?-tetra(tert-butyl)-3, 3′,3″,3?-tetra(phenylthio)phthalocyanine
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The reaction of acidic form of the substituted iron phthalocyanine complex (3-PhS-5-But)4pc′Fe (pc″Fe) with dioxygen in o-dichlorobenzene in the presence of dichloroacetic acid (HX) was investigated. The oxidation of Hpc″FeX gives the corresponding radical cation, which was confirmed by the stoichiometry of reduction of the product formed in this reaction with a two-electron reducing agent. The kinetic equation obtained on the basis of dependences of the oxidation rate on the Hpc″FeX, HX, and O2 concentrations are consistent with the reaction mechanism that implies the formation of a Hpc″FeX complex with O2 and its transformation to give a radical cation under the action of HX.
- Fedorova,Topol',Derkacheva,Luk'yanets,Kaliya
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- ESR study of the thermal decomposition of di-tert-butoxy-tert-butyl alumotrioxide formed in the reaction of tri-tert-butoxyaluminum with tert-butyl hydroperoxide
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Tri-tert-butoxyaluminum reacts with tert-butyl hydroperoxide to produce di-tert-butoxy-tert-butyl alumotrioxide, which decomposes heterolytically to form singlet dioxygen and homolytically with the O-O bond cleavage. The ButOO , (But
- Stepovik, L. P.,Martinova, I. M.,Dodonov, V. A.,Cherkasov, V. K.
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- Stoichiometry and Rate of Reaction of Hydrogen Atoms with Oxygen
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The reaction of hydrogen atoms (1E-6-1E-5mol dm-3) with oxygen (0-1E-5mol dm-3) in excess argon has been studied in a fast flow-discharge tube at total pressures from 2 to 10 Torr and temperatures from 231 to 512 K using mass spectrometry and gas chromatography for final-product analysis.A method of measuring small concentrations of water (ca. 1E-7mol dm-3) has been developed which enabled the relative rates of reactions (2) and (3) to be determined, reaction (4) being negligible:+Ar->HO2+Ar (1); H+HO2->(2); H+HO2->2OH (3); H+HO2->H2O+O.Over the range 231(errors throughout are standard deviations.An improved Arrhenius expression for reaction (1) has been determined: .Previous evaluations of rate data for step (3) are discussed and revised values suggested:.
- Pratt, Graham L.,Wood, Stephen W.
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- Measurements and modeling of HO2 formation in the reactions of n-C3H7 and i-C3H7 radicals with O2
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The formation of HO2 in the reactions of C2H 5, n-C3H7, and i-C3H7 radicals with O2 is investigated using the technique of laser photolysis/long-path frequency-modulation spectroscopy. The alkyl radicals are formed by 266 nm photolysis of alkyl iodides. The formation of HO2 from the subsequent reaction of the alkyl radicals with O2 is followed by infrared frequency-modulation spectroscopy. The concentration of I atoms is simultaneously monitored by direct absorption of a second laser probe on the spin-orbit transition. The measured profiles are compared to a kinetic model taken from time-resolved master-equation results based on previously published ab initio characterizations of the relevant stationary points on the potential-energy surface. The ab initio energies are adjusted to produce agreement with the present experimental data and with available literature studies. The isomer specificity of the present results enables refinement of the model for i-C3H7 + O2 and improved agreement with experimental measurements of HO2 production in propane oxidation. ? 2005 American Chemical Society.
- Estupinì?aì?n, Edgar G.,Klippenstein, Stephen J.,Taatjes, Craig A.
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- Rate Constant and Possible Pressure Dependence of the Reaction OH+HO2
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The technique of laser-induced fluorescence has been used to measure steady-state OH concentrations in the photolysis of water vapor at 184.9 nm and 298 K, with O2 added in trace amounts.He or Ar was present at total pressures in the range 75-730 torr.The results were used to derive the rate-constant ratio k1/k51/2, where k1 and k5 are the rate constants for the reactions OH+HO2->H2O+O2 and HO2+HO2->O2, respectively.When currently available values for k5 are used, the results give k1=(1.2+/-0.4)x10-10 cm3s-1 at 1-atm pressure, with evidence of a decline of k1 at lower pressures.No water-vapor effect on k1 was observed.
- DeMore, W. B.
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- Mechanisms of HO2(A2A') Excitation in Various Chemical Systems
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Chemiluminescence from electronically excited HO2 has been detected between 800 and 1200 nm in various gas-phase flow systems using a near-infrared-sensitive photomultiplier.The emission essentially consists of ν3 sequences of the HO2(A2A' -> X2A ) transition.From spectroscopic and kinetic evidence it is concluded that, in addition to the previously suggested excitation of thermal HO2 by O2(1Δ), at least two mechanisms are responsible for the formation of HO2(2A',ν3'a mechanism involving the consecutive excitation of one HO2 molecule by two O2(1Δ) molecules and (ii) the thermal recombination of H atoms with O2.
- Holstein, K. J.,Fink, E. H.,Wildt, J.,Winter, R.,Zabel, F.
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- Kinetics of O(3PJ) Reactions with H2O2 and O3
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The kinetics of the reactions O(3PJ) + H2O2 -> products (k1) and O(3PJ) + O3 -> 2O2 (k2) have been investigated as a function of temperature over the temperature ranges 298-386 and 237-377 K, respectively.O(3PJ) was produced in the absence of other reactive free radicals by 532-nm pulsed laser photolysis of O3 and detected by time-resolved resonance fluorescence spectroscopy.The following Arrhenius expressions adequately describe the experimental results: k1=(1.13 +/- 0.54)*10-12 exp and k2=(5.6 +/- 2.1)*10-12 exp (units are cm3 molecule-1 s-1, errors are 2?).
- Wine, P. H.,Nicovich, J. M.,Thompson, R. J.,Ravishankara, A. R.
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- Infrared frequency-modulation probing of product formation in alkyl + O2 reactions: III. The reaction of cyclopentyl radical (c-C5H9) with O2 between 296 and 723 K
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The production of HO2 from the reaction of c-C5H9 + O2 has been investigated as a function of temperature (296-723 K) by using laser photolysis/CW infrared frequency modulation spectroscopy. The HO2 yield is derived by comparison with the Cl2/CH3OH/O2 system and is corrected to account for HO2 signal loss due to competing reactions involving HO2 radical and the adduct c-C5H9O2. The time behavior of the HO2 signal following cyclopentyl radical formation displays two separate components. The first component is a prompt production of HO2, which increases with temperature and is the only component observed between 296 and 500 K. The yield from the prompt production rises from less than 1% at 296 K to ~23% at 693 K. At temperatures above 500 K a second slower rise in the HO2 signal is also observed. The production of HO2 on a slower time scale is attributable to cyclopentylperoxy radical decomposition. The total HO2 yield, including the contribution from the slower rise, increases dramatically with temperature from ~2% at 500 K to ~100% at 683 K. From 683 to 723 K the total HO2 yield remains constant. The second slower rise accounts for a majority of the product formation at these higher temperatures. The biexponential time behavior of the HO2 production from c-C5H9 + O2 is similar to that previously observed in studies of C2H5 + O2 and C3H7 + O2 reactions. The rate of formation for delayed HO2 production from c-C5H9 + O2 is larger than the rate of formation from either C2H5 + O2 or C3H7 + O2 at each temperature. However, apparent activation energies, obtained by an Arrhenius plot of the rates of formation for delayed HO2 formation, are very similar for the three systems (C2H5 + O2, C3H7 + O2, and c-C5H9 + O2). The results suggest a similar coupled mechanism for HO2 production in the C2H5 + O2, C3H7 + O2, and c-C5H9 + O2 reactions, with concerted elimination of HO2 from the RO2 radical responsible for HO2 + alkene production.
- DeSain, John D.,Taatjes, Craig A.
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- Role of interstitial voids in oxides on formation and stabilization of reactive radicals: Interstitial HO2 radicals in F2-laser- irradiated amorphous SiO2
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A procedure to produce stable hydroperoxy radicals (HO2 .) in bulk amorphous SiO2 (a-SiO2) has been developed. Oxygen molecules incorporated in the interstitial voids in a-SiO 2 react with mobile hydrogen atoms (H0) generated by the photolysis of silanol (SiOH) groups with F2-laser light (λ = 157 nm, hν = 7.9 eV), resulting in the efficient creation of interstitial HO2.. The high yield of HO2. suggests that the collisions of the reaction intermediate with the void wall play an important role in dissipating the excess energy of the intermediate instead of the triple collision observed in the gas phase reaction. The resultant HO2. is thermally stable up to 100 °C.
- Kajihara, Koichi,Hirano, Masahiro,Skuja, Linards,Hosono, Hideo
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- Rate Constants of the Reaction of the Hydrated Electron and Hydroxyl Radical with Ozone in Aqueous Solution
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Absolute rate constants for the reaction of the hydrated electron and hydroxyl radical with ozone in aqueous solution have been determined by using pulse radiolysis techniques.The rate constant, k(eaq-+O3)=(3.60+/-0.14)*1010 dm3 mol-1 s-1, was measured in the pH range 4.1-6.05 by following the decay of eaq- at 600 nm.The rate constant k(OH.+O3)=(3.02+/-0.25)*109 dm3 mol-1 s-1, was obtained by a competition method at pH 6.7 with acetate ions as the OH. radical scavangers.The ozone concentration for both studies varied from 0.05*10-3 to 0.50*10-3 mol dm-3.
- Bahnemann, D.,Hart, Edwin J.
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- Rate Constants for the Reaction HO2 + NO2 + N2 -> HO2NO2 + N2: The Temperature Dependence of the Falloff Parameters
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Rate constants for the title reaction were measured by flash photolysis ultraviolet absorption spectroscopy at N2 pressures of 25, 50, and 100 Torr over the temperature range 228-358 K.The data were fit to an expression suitable for describing the pressure dependence of reactions in the falloff region with the temperature dependence of the falloff parameters given by k0,N2(T) = k0,N2(300K)-n and kinfinite(T) = kinfinite(300K)-m.The inert gas pressures in this study were low enough to permit a precise determination of n (which describes the temperature dependence of the low-pressure, limiting third-order rate constant).The same rate constant data, however, were less sensitive to the determination of m (associated with the limiting high-pressure rate constant).For this reason, our final analysis utilizes a composite fit of our temperature dependent data along with similar data at 100 and 700 Torr of N2 obtained by Sander and Peterson to yield k0,N2(T) = 1.8 * 10-31-(3.2+/-0.4) cm6 molecule-2 s-1 and kinfinite(T) = 4.7 * 10-12-(1.4+/-1.0) cm3 molecule-1 s-1.
- Kurylo, Michael J.,Ouellette, Philip A.
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- Measurements of Line Strengths in the HO2 ν1 Overtone Band at 1.5 μm Using an InGaAsP Laser
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We report the first observation of resolved rotational-vibrational overtone (2ν1) absorptions of the hydroperoxyl radical (HO2) in the 1.5-μm region, using two-tone frequency modulation spectroscopy (TTFMS) with an InGaAsP laser diode and White-cell optics.Photolysis of Cl2/H2/O2 mixtures was used to produce the HO2, and the concentration was determined by modulated-photolysis UV absorption spectroscopy.The line center absorption cross sections for the strongest line ranged between 1.3x10-20 and 10x10-20 cm2 molecule-1 under Doppler-limited conditions.For the strongest line corresponds to an integrated line strength S of 1.6x10-21 cm2 molecule-1cm-1, a line strength of the same order of magnitude as lines previously observed in the relatively weak ν1 fundamental.
- Johnson, T. J.,Wienhold, F. G.,Burrows, J. P.,Harris, G. W.,Burkhard, H.
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- Rate Constants for H +O2 + M at 298 K for M = He, N2, and H2O
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The rate constants of the three-body recombination reaction H + O2 + M (M = He, N2, H2O) were measured from 4.79 to 30.1 Torr at room temperature by the discharge-flow technique.The respective rate constants obtained are (2.6 +/- 0.2)E-32, (6.1 +/- 0.9)E-32, and (6.4 +/- 0.8)E-31 cm6s-1.Although the rates for He and N2 can be rationalized in terms of existing theory, that for H2O implies a collision efficiency greater than 1.This situation can be rectified by use of the total quantum mechanical scattering cross section instead of the Lennard-Jones cross section commonly used.
- Hsu, K.-J.,Durant, J. L.,Kaufman, F.
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- The HOO complex with SO2, a matrix isolation study
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The complex formation between HOO and SO2 in argon matrices has been studied with FTIR spectroscopy. The complex shifts of the intramolecular fundamentals of the complex components suggest the formation of a complex, where HOO acts as a lone pair donor to the sulfur atom of SO2 while its hydrogen atom is sufficiently close to one of the oxygen atoms of SO2 to give a significant blue shift of the HOO bend. The complex is rapidly decomposed by irradiation at 266 nm. A comparison between the spectrum of the photoproduct and the spectrum of matrix isolated sulfuric acid suggests the possibility that the photoproduct is the radical formed by dissociation of one of the OH bonds of sulfuric acid.
- Svensson, Thomas,Nelander, Bengt
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- Nanoscale Metal-Organic Frameworks Stabilize Bacteriochlorins for Type i and Type II Photodynamic Therapy
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Herein we report the design of a bacteriochlorin-based nanoscale metal-organic framework, Zr-TBB, for highly effective photodynamic therapy via both type I and type II mechanisms. The framework of Zr-TBB stabilizes 5,10,15,20-tetra(p-benzoato)bacteriochlorin (TBB) ligands toward oxygen and light via geometrical constraint. Upon 740 nm light irradiation, Zr-TBB efficiently generates various reactive oxygen species, including singlet oxygen, superoxide anion, hydrogen peroxide, and hydroxyl radicals, to afford superb antitumor efficacy on mouse models of breast and colon cancers, with cure rates of 40% and 60%, respectively.
- Luo, Taokun,Ni, Kaiyuan,Culbert, August,Lan, Guangxu,Li, Zhe,Jiang, Xiaomin,Kaufmann, Michael,Lin, Wenbin
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supporting information
p. 7334 - 7339
(2020/08/21)
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- Titanium-Based Nanoscale Metal-Organic Framework for Type i Photodynamic Therapy
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Nanoscale metal-organic frameworks (nMOFs) have shown great potential as nanophotosensitizers for photodynamic therapy (PDT) owing to their high photosensitizer loadings, facile diffusion of reactive oxygen species (ROSs) through their porous structures, and intrinsic biodegradability. The exploration of nMOFs in PDT, however, remains limited to an oxygen-dependent type II mechanism. Here we report the design of a new nMOF, Ti-TBP, composed of Ti-oxo chain secondary building units (SBUs) and photosensitizing 5,10,15,20-tetra(p-benzoato)porphyrin (TBP) ligands, for hypoxia-tolerant type I PDT. Upon light irradiation, Ti-TBP not only sensitizes singlet oxygen production, but also transfers electrons from excited TBP? species to Ti4+-based SBUs to afford TBP?+ ligands and Ti3+ centers, thus propagating the generation of superoxide, hydrogen peroxide, and hydroxyl radicals. By generating four distinct ROSs, Ti-TBP-mediated PDT elicits superb anticancer efficacy with >98% tumor regression and 60% cure rate.
- Lan, Guangxu,Ni, Kaiyuan,Veroneau, Samuel S.,Feng, Xuanyu,Nash, Geoffrey T.,Luo, Taokun,Xu, Ziwan,Lin, Wenbin
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supporting information
p. 4204 - 4208
(2019/03/11)
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- Precursor-mediated synthesis of Cu2-xSe nanoparticles and their composites with TiO2 for improved photocatalysis
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The direct synthesis of copper selenide nanoparticles from the reaction of ditertiarybutyl selenide tBu2Se with copper(ii) trifluoroacetate Cu(TFA)2 under mild conditions is reported. The isolation of a molecular species d
- Gahlot, Sweta,Jeanneau, Erwann,Dappozze, Frederic,Guillard, Chantal,Mishra, Shashank
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supporting information
p. 8897 - 8905
(2018/07/25)
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- Photooxygenation of oxygen-substituted naphthalenes
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The reaction of oxygen-substituted naphthalenes with singlet oxygen (1O2) has been investigated, and labile endoperoxides have been isolated and characterized at –78°C for the first time. Low-temperature kinetics by UV spectroscopy revealed that alkoxy and silyloxy substituents remarkably increase the rate of photooxygenations compared to 1,4-dimethylnaphthalene, whereas acyloxy-substituted acenes are inert towards 1O2. The reactivities nicely correlate with HOMO energies and free activation energies, which we determined by density functional theory calculations. The lability of the isolated endoperoxides is due to their very fast back reaction to the corresponding naphthalenes even at –20°C under release of 1O2, making them to superior sources of this reactive species under very mild conditions. Finally, a carbohydrate-substituted naphthalene has been synthesized, which reacts reversibly with 1O2 and might be applied for enantioselective oxidations in future work.
- Bauch, Marcel,Krtitschka, Angela,Linker, Torsten
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- Quantitative measurements of HO2 and other products of n -butane oxidation (H2O2, H2O, CH2O, and C2H4) at elevated temperatures by direct coupling of a jet-stirred reactor with sampling nozzle and cavity ring-down spectroscopy (cw-CRDS)
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For the first time quantitative measurements of the hydroperoxyl radical (HO2) in a jet-stirred reactor were performed thanks to a new experimental setup involving fast sampling and near-infrared cavity ring-down spectroscopy at low pressure. The experiments were performed at atmospheric pressure and over a range of temperatures (550-900 K) with n-butane, the simplest hydrocarbon fuel exhibiting cool flame oxidation chemistry which represents a key process for the auto-ignition in internal combustion engines. The same technique was also used to measure H2O2, H2O, CH2O, and C2H4 under the same conditions. This new setup brings new scientific horizons for characterizing complex reactive systems at elevated temperatures. Measuring HO2 formation from hydrocarbon oxidation is extremely important in determining the propensity of a fuel to follow chain-termination pathways from R + O2 compared to chain branching (leading to OH), helping to constrain and better validate detailed chemical kinetics models.
- Djehiche, Mokhtar,Le Tan, Ngoc Linh,Jain, Chaithanya D.,Dayma, Guillaume,Dagaut, Philippe,Chauveau, Christian,Pillier, Laure,Tomas, Alexandre
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p. 16689 - 16694
(2015/02/02)
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- Photolysis of endoperoxides in the presence of nitroxides: A laser flash photolysis study with optical and ESR detection
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Time-resolved electron paramagnetic resonance spectroscopy, transient absorption, and phosphorescence spectroscopy were used to investigate the spin polarization of a nitroxide free radical induced by interaction with singlet oxygen (1O2). The latter was generated by photolysis of endoperoxides of two anthracene derivatives. Although both anthracene endoperoxides are structurally similar, opposite spin polarization of the nitroxide was observed. Photolysis of one endoperoxide leads to absorptive nitroxide spin polarization due to interaction with the generated 1O2. Photolysis of the other endoperoxide generated emissive nitroxide spin polarization, probably due to interaction of the endoperoxide triplet states with nitroxides. The Royal Society of Chemistry and Owner Societies.
- Moscatelli, Alberto,Sartori, Elena,Ruzzi, Marco,Jockusch, Steffen,Lei, Xuegon,Khudyakov, Igor,Turro, Nicholas
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p. 205 - 210
(2014/02/14)
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- Radical product yields from the ozonolysis of short chain alkenes under atmospheric boundary layer conditions
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The gas-phase reaction of ozone with unsaturated volatile organic compounds (VOCs), alkenes, is an important source of the critical atmospheric oxidant OH, especially at night when other photolytic radical initiation routes cannot occur. Alkene ozonolysis is also known to directly form HO2 radicals, which may be readily converted to OH through reaction with NO, but whose formation is poorly understood. We report a study of the radical (OH, HO 2, and RO2) production from a series of small alkenes (propene, 1-butene, cis-2-butene, trans-2-butene, 2-methylpropene, 2,3-dimethyl-2-butene (tetramethyl ethene, TME), and isoprene). Experiments were performed in the European Photoreactor (EUPHORE) atmospheric simulation chamber, with OH and HO2 levels directly measured by laser-induced fluorescence (LIF) and HO2 + ΣRO2 levels measured by peroxy-radical chemical amplification (PERCA). OH yields were found to be in good agreement with the majority of previous studies performed under comparable conditions (atmospheric pressure, long time scales) using tracer and scavenger approaches. HO2 yields ranged from 4% (trans-2-butene) to 34% (2-methylpropene), lower than previous experimental determinations. Increasing humidity further reduced the HO2 yields obtained, by typically 50% for an RH increase from 0.5 to 30%, suggesting that HOx production from alkene ozonolysis may be lower than current models suggest under (humid) ambient atmospheric boundary layer conditions. The mechanistic origin of the OH and HO2 production observed is discussed in the context of previous experimental and theoretical studies.
- Alam, Mohammed S.,Rickard, Andrew R.,Camredon, Marie,Wyche, Kevin P.,Carr, Timo,Hornsby, Karen E.,Monks, Paul S.,Bloss, William J.
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p. 12468 - 12483
(2014/01/06)
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- Spectroscopic and kinetic properties of HO2 radicals and the enhancement of the HO2 Self reaction by CH3OH and H 2O
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The line center absorption cross sections and the rate constants for self-reaction of hydroperoxy radicals (HO2) have been examined in the temperature range of 253-323 K using pulsed laser photolysis combined with tunable diode laser absorption in the near-IR region. The transition prohed was in the 2v1 OH overtone transition at 1506.43 nm. The temperature dependence of the rate constant (k) for the HO2 + HO2 reaction was measured relative to the recommended value at 296 K, giving k = (3.95 ± 0.45) × 10-13 × exp[(439 ± 39)/7]cm3 molecule-1 s-1 at a total pressure of 30 Torr (N2 + O2). After normalizing our determination and previous studies at low pressure, we recommend k = (2.45 ± 0.50)× 10-13 × exp[(565 ± 130)/T]cm3 molecule-1 s-1 (0 obs, increases linearly with CH 3OH concentration, and the enhancement coefficient (k'), defined by kobs = k + k;[CH3OH], is found to be (3.90 ± 1.87) × 10-35 × exp[(3849 ± 135)/T]cm6 molecule-2 s-1 at 30 Torr. The analogous water vapor enhancement coefficient (k′) is (1.16 ± 0.58) × 10-36 × exp[(4614 ± 145)/T]cm6 molecule-2 s-1. The pressure-broadened HO2 absorption cross section is independent of temperature in the range studied. The line center absorption cross sections at 1506.43 nm, after correction for instrumental broadening, are (4.3 ± 1.1) × 10-19, (2.8 ± 0.7) × 10-19, and (2.0 ± 0.5) × 10-19 cm2/molecule at total pressures of 0, 30, and 60 Torr, respectively (95% confidence limits).
- Tang, Yongxin,Tyndall, Geoffrey S.,Orlando, John J.
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p. 369 - 378
(2010/06/16)
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- Matrix-isolation infrared spectra of HOOBr and HOBrO produced upon VUV light irradiation of HBr/O2/Ne system
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Vacuum ultraviolet (VUV) light photolysis of an HBr/O2 mixture in a Ne matrix has produced HO2Br isomers (HOOBr and HOBrO), which are important reaction intermediates in atmospheric chemistry. The observed bands have been assigned with an aid of a quantum chemical calculation at CCSD/aug-cc-pVDZ. These assignments have been confirmed by the experimental results using isotopic species of 18O2 or DBr. Their characteristic bands are discussed in comparison with those of HOOCl and HOClO from an HCl/O2 mixture [7]. Both HOOBr and HOBrO are found to be photolyzed with the UV light below 385 nm.
- Akai, Nobuyuki,Wakamatsu, Daisuke,Yoshinobu, Takeo,Kawai, Akio,Shibuya, Kazuhiko
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p. 117 - 120
(2011/01/05)
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- Photon-initiated homolysis of peroxynitrous acid
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Laser flash photolysis of ONOOH at 355 nm and a pH of 4.0-5.5 causes homolysis of ONOOH nearly exclusively at the N-O bond rather than at the O-O bond (HO2?/HO? > 25:1). All of the NO? and HO2?/
- Sturzbecher-Hoehne, Manuel,Nauser, Thomas,Kissner, Reinhard,Koppenol, Willem H.
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p. 7307 - 7312
(2009/12/08)
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- Overtone dissociation of peroxynitric acid (HO2NO2): Absorption cross sections and photolysis products
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Band strengths for the second (3vOH) and third (4VOH) overtones of the OH stretch vibration of peroxynitric acid, HO 2NO2 (PNA) in the gas-phase were measured using Cavity Ring-Down Spectroscopy (CRDS). Both OH overtone transitions show diffuse smoothly varying symmetrical absorption profiles without observable rotational structure. Integrated band strengths (base e) at 2% K were determined to be S3vOH = (5.7 ± 1.1) × 10-20 and S 4vOH = (4.9 ± 0.9) × 10-21 cm2 molecule-1 cm-1 with peak cross sections of (8.8 ± 1.7) × 10-22 and (7.0 ± 1.3) × 10-23 cm2 molecule-1 at 10086.0 ± 0.2 cm-1 and 13095.8 ± 0.4 cm-1, respectively, using PNA concentrations measured on line by Fourier-transform infrared and ultraviolet absorption spectroscopy. The quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors in the measurements. OH overtone spectra measured at lower temperature, 231 K, showed a narrowing of the 3vOH band along with an increase in its peak absorption cross section, but no change in S3vOH to within the precision of the measurement (±9%). Measurement of a PNA action spectrum showed that HO2 is produced from second overtone photodissociation. The action spectrum agreed with the CRDS absorption spectra. The PNA cross sections determined in this work for 3v OH and 4vOH will increase calculated atmospheric photolysis rates of PNA slightly.
- Stark, Harald,Brown, Steven S.,Burkholder, James B.,Aldener, Mattias,Riffault, Veronique,Gierczak, Tomasz,Ravishankara
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p. 9296 - 9303
(2009/03/12)
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- Titanium tetra-tert-butoxide-tert-butyl hydroperoxide oxidizing system: Physicochemical and chemical aspects
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The reaction of titanium tetra-tert-butoxide with tert-butyl hydroperoxide (1: 2) (C6H6, 20 C) involves the steps of formation of the titanium-containing peroxide (t-BuO)3TiOOBu-t and peroxytrioxide (t-BuO)3TiOOOBu-t. The latter decomposes with the release of oxygen, often in the singlet form, and also homolytically with cleavage of both peroxy bonds. The corresponding alkoxy and peroxy radicals were identified by ESR using spin traps. The title system oxidizes organic substrates under mild conditions. Depending on the substrate structure, the active oxidant species can be titanium-containing peroxide, peroxytrioxide, and oxygen generated by the system.
- Stepovik,Gulenova,Martynova,Mar'Yasin,Cherkasov
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p. 266 - 276
(2008/09/20)
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- Formation of H O2 radicals from the photodissociation of H2 O2 at 248 nm
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New experiments have been performed in order to evaluate the primary quantum yield of pathway by direct observation of HO2 radical formation after photolysis of H2O2 at 248 nm. The quantum yield for OH production at 248 nm has been determined by two different groups including Vaghijani and Ravishankara who have measured the quantum yields of OH, 0, and H relative to the known quantum yields of 03 and CH 3SH photolysis and have obtained a quantumyield. The IUPAC subcommittee has also recommended a quantum yield of t wo OH radicals at photolysis wavelengths of λ>230 nm. Part of theHe flow in some experiments has been replaced by O2.
- Thiebaud, Jerome,Aluculesei, Alina,Fittschen, Christa
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- Formation of HO2 and OH in photolytically initiated oxidation of dimethyl ether
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Time-resolved measurements of HO2 and OH have been conducted in 355 nm photolysis of dimethyl ether/Cl2/O2 mixture at elevated temperature, using near-infrared frequency modulation spectroscopy. A part of OH was found to be produced at a timescale of several microseconds by the methoxymethyl with O2 reaction, while HO2 is formed mainly in milliseconds with the yield increasing up to 60% between 500 and 600 K. It was rationalized that HO2 is not a direct product of the O2 adduct decomposition, but a secondary product through HCHO + OH reaction. Another pathway through HCO formation from the adduct is also discussed.
- Suzaki, Kotaro,Kanno, Nozomu,Tonokura, Kenichi,Koshi, Mitsuo,Tsuchiya, Kentaro,Tezaki, Atsumu
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p. 179 - 184
(2008/10/09)
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- Reflected shock tube studies of high-temperature rate constants for OH + NO2 -HO2 + NO and OH + HO2 ± H 2O + O2
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The motivation for the present study comes from the preceding paper where it is suggested that accepted rate constants for OH + NO2 + NO → HO2 are high by ~2. This conclusion was based on a reevaluation of heats of formation for HO2, OH, NO, and NO2 using the Active Thermochemical Table (ATcT) approach. The present experiments were performed in C2H5I/NO2 mixtures, using the reflected shock tube technique and OH-radical electronic absorption detection (at 308 nm) and using a multipass optical system. Time-dependent profile decays were fitted with a 23-step mechanism, but only OH + NO2, OH + HO 2, both HO2 and NO2 dissociations, and the atom molecule reactions, O + NO2 and O + C2H4, contributed to the decay profile. Since all of the reactions except the first two are known with good accuracy, the profiles were fitted by varying only OH + NO2 and OH + HO2. The new ATcT approach was used to evaluate equilibrium constants so that back reactions were accurately taken into account. The combined rate constant from the present work and earlier work by Glaenzer and Troe (GT) is kOH+NO2 = 2.25 × 10 -11 exp(-3831 K/T) cm3 molecule-1 s -1, which is a factor of 2 lower than the extrapolated direct value from Howard but agrees well with NO + HO2 → OH + NO2 transformed with the updated equilibrium constants. Also, the rate constant for OH + HO2 suitable for combustion modeling applications over the T range (1200-1700 K) is (5 ± 3) × 1011 cm3 molecule-1 s-1. Finally, simulating previous experimental results of GT using our updated mechanism, we suggest a constant rate for k HO2+NO2 = (2.2 ± 0.7) ± 10-11 cm3 molecule-1 s 1 over the T range 1350-1760 K.
- Srinivasan, Nanda K.,Su, Meng-Chih,Sutherland, James W.,Michael, Joe V.,Ruscic, Branko
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p. 6602 - 6607
(2008/10/09)
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- Thermal decomposition of HO2NO2 (peroxynitric acid, PNA): Rate coefficient and determination of the enthalpy of formation
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Rate coefficients for the gas-phase thermal decomposition of HO 2NO2 (peroxynitric acid, PNA) are reported at temperatures between 331 and 350 K at total pressures of 25 and 50 Torr of N2. Rate coefficients were determined by measuring the steady-state OH concentration in a mixture of known concentrations of HO2NO 2 and NO. The measured thermal decomposition rate coefficients k -1(T,P) are used in combination with previously published rate coefficient data for the HO2NO2 formation reaction to yield a standard enthalpy for reaction 1 of ΔrH°298 K = -24.0 ± 0.5 kcal mol-1 (uncertainties are 2σ values and include estimated systematic errors). A HO2NO2 standard heat of formation, ΔfH°(HO2NO 2), of -12.6 ± 1.0 kcal mol-1 was calculated from this value. Some of the previously reported data on the thermal decomposition of HO2NO2 have been reanalyzed and shown to be in good agreement with our reported value.
- Gierczak, Tomasz,Jimenez, Elena,Riffault, Veronique,Burkholder, James B.,Ravishankara
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p. 586 - 596
(2007/10/03)
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- A kinetic and product study of the Cl + HO2 reaction
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The absolute rate data and product branching ratios for the reactions Cl+HCl→HCL+O2 and Cl+HO2→OH+ClO were measured. The measurement of consumption of HO2 in excess Cl yielded K la and the measurement of the consumption of Cl in excess HO 2 yielded a total rate coefficient. For the product measurement, an excess of Cl was added to known concentrations of HO2 and the reaction was allowed to reach completion. Numerical simulations were used to check the interferences from secondary chemistry in both the kinetic and product experiments and also to quantify the losses incurred during the conversion process HO2→OH for detection purposes.
- Hickson, Kevin M.,Keyser, Leon F.
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p. 6887 - 6900
(2008/10/09)
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- High temperature rate coefficient measurements of H + O2 chain-branching and chain-terminating reaction
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Rate coefficients for H + O2 → OH + O (R1) and H + O2 + M → HO2 + M (R9) were measured via OH absorption behind reflected shock waves, being: k1 = 6.73 × 1015 T-0.50 e
- Hwang,Ryu, Si-Ok,Witt, K.J. De,Rabinowitz
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p. 107 - 111
(2008/10/09)
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- Reaction of OH with HO2NO2 (Peroxynitric Acid): Rate Coefficients between 218 and 335 K and Product Yields at 298 K
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HO2NO2 (peroxynitric acid, PNA) has an important role in determining the ozone abundance and its changes over time in the lower stratosphere. Rate coefficients (k3(T)) for the reaction of OH with PNA in the gas phase were
- Jimenez, Elena,Gierczak, Tomasz,Stark, Harald,Burkholder, James B.,Ravishankara
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p. 1139 - 1149
(2007/10/03)
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- Potassium peroxostannate decomposition in an alkaline medium
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The catalytic decomposition of potassium peroxostannate aqueous solutions in the range pH 8-13 is studied. Iron(II), iron(III), and nickel(II) ions differently affect the decomposition. Hydroxo and hydroperoxo radicals are shown to form in the course of K2Sn(OOH)6 decomposition. The kinetic parameters of the reaction are calculated.
- Ippolitov,Kabluchaya,Shlyakhova
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p. 649 - 652
(2008/10/09)
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- Oscillatory reactions Am(VI) ? Am(V) under ozonation of Am(OH) 3 suspension in bicarbonate solution
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During prolonged ozonation of Am(III) hydroxide in bicarbonate solutions, oscillatory Am(VI) ? Am(IV) reactions were observed. Substitution of 241Am with 243Am, which is characterized by substantially lower specific radioactivity, does not change the character and parameters of the oscillatory process: the yields of 241Am and 243Am, and the oscillation period of about 2 min do not differ noticeably. The results suggest that the reductants in the system mainly originate from the ozone decomposition products; the arising hydroperoxy radicals and hydrogen peroxide partially reduce Am(VI) in the solution. The Am(VI) yield in ozonation of the Am(OH)3 suspension in a bicarbonate solution substantially decreases with increasing the initial americium content.
- Nikonov,Gogolev,Tananaev,Myasoedov
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p. 246 - 248
(2008/10/09)
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- Low-temperature kinetics of the reaction of the OH radical with hydrogen peroxide
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The kinetics of the reaction of the OH radical with hydrogen peroxide, H2O2, are studied over a temperature range of 96-296 K. The low-temperature environment is provided by a pulsed Laval nozzle supersonic expansion of nitrogen with admixed H2O2. Hydrogen peroxide serves as both the OH radical photolytic precursor (λ = 248 nm) and a reactant. Laser-induced fluorescence of the OH radicals excited in the (1,0) band of the A2Σ+-X2Π1 transition is used to monitor the kinetics of OH removal. The rate coefficient of the OH + H2O2 reaction (k1) shows a negative temperature dependence within this temperature range, which can be expressed as k1 = (6.8 ± 1.0) × 10-13 exp[(285 ± 27)/T] cm3 molecule-1 s-1. The combined low- and high-temperature (literature) kinetic data form a U-shaped Arrhenius plot, which suggests that the reaction mechanism changes from direct abstraction (at high temperatures) to a mechanism involving formation of a hydrogen-bonded complex (at low temperatures). Atmospheric implications of the new low-temperature kinetic data are discussed.
- Vakhtin, Andrei B.,McCabe, David C.,Ravishankara,Leone, Stephen R.
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p. 10642 - 10647
(2007/10/03)
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- Experimental and theoretical characterization of H2OOO +
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This report presents the preparation and characterization of H2OOO+, an important intermediate in water-oxygen chemistry. The H2OOO+ cation was produced by co-deposition of H2O/Ar with radio frequency discharged O2/Ar at 4 K and was identified by four fundamental infrared absorptions. Quantum chemical calculations indicate a doublet ground state with a H2O-O2hemi-bonded Cs structure. Copyright
- Zhou, Mingfei,Zeng, Aihua,Wang, Yun,Kong, Qingyu,Wang, Zhi-Xiang,Van Rague Schleyer, Paul
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p. 11512 - 11513
(2007/10/03)
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- A neutral xenon-containing radical, HXeO
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We report an open-shell species containing xenon, HXeO (2Σ), prepared by UV photolysis of H2O/Xe or N2O/HBr/Xe solid mixtures at 7 K and subsequent thermal mobilization of oxygen atoms at ≥30 K. The H-Xe stretching absorption of HXeO in solid Xe is at 1466.1 cm-1, and it shifts to 1070.3 cm-1 upon deuteration. The extensive ab initio calculations indicate that HXeO is intrinsically stable, owing to significant ionic and covalent contributions to its bonding. The formation of HXeO (2Σ) radicals in these experiments suggests extensive stabilization and thermal mobility of singlet (1D) oxygen atoms in solid Xe and holds promises for the stability of the HKrO and HArO species. Copyright
- Khriachtchev, Leonid,Pettersson, Mika,Lundell, Jan,Tanskanen, Hanna,Kiviniemi, Tiina,Runeberg, Nino,Raesaenen, Markku
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p. 1454 - 1455
(2007/10/03)
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- Kinetics and Mechanism of HO2 uptake on solid NaCl
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The interaction of HO2 radicals with solid NaCl has been investigated. The uptake coefficient γ was measured using a coaxial reactor with a movable central rod covered with NaCl. The radicals were detected at low concentrations (~4 × 1010 molecule/cm3) by matrix isolation ESR and at high concentrations (~5 × 1011 molecule/cm3) by titration with NO followed by gas-phase EPR detection. In the temperature range from 243 to 295 K, the apparent activation energy of γ does not depend on the HO2 concentration. The γ value measured on NaCl agrees well with our previous γ value for nonreactive uptake by NH4NO3 in this temperature range. Furthermore, in the temperature range from 331 to 335 K, the γ value decreases sharply at low HO2 concentrations. A combined Eley-Rideal and Langmuir-Hinshelwood mechanism with reasonable parameter values can explain the observations; such a mechanism is also consistent with the observation of an inhibition effect of water vapor on the uptake coefficient. The conclusion is that, in the coastal troposphere, the heterogeneous loss of HO2 is of comparable importance to the homogeneous loss, particularly in the evening, when the HO2 concentration is low.
- Remorov,Gershenzon,Molina,Molina
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p. 4558 - 4565
(2007/10/03)
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- NO2 quantum yield from the 248 nm photodissociation of peroxynitric acid (HO2NO2)
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Investigations of the atmospheric impacts of aircraft emissions, industrial, and agricultural emission, and changes in the radiative balance of the atmosphere invariably focus on the chemical mechanisms, which control the production and loss of O3. The quantum yield of NO2 production from peroxynitric acid (PNA) photodissociation at 248 nm was determined by comparison to HNO3photolysis data taken under identical experimental conditions. Measurements made over a range of pressures, flows, and precursor concentrations resulted in an NO2 yield of 0.56 ± 0.17. Calculations of potential energy curves for several low-lying singlet and triplet states of PNA showed that while the singlet excitations occurred via an n-π* transition on the NO2 moiety, the dissociative channels forming OH + NO3 and HO2 + NO2 occurred via predissociation on different surfaces. Excitation energies at the multireference internally contracted configuration interaction and CCSD(T) showed that excited states of PNA were not accessible at wavelengths longer than 407 nm.
- Roehl, Coleen M.,Mazely, Troy L.,Friedl, Randall R.,Li, Yumin,Francisco, Joseph S.,Sander, Stanley P.
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p. 1592 - 1598
(2007/10/03)
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- Kinetic study of the reactions of BrO radicals with HO2 and DO2
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The kinetics of the reactions of BrO radicals with HO2 and DO2 radicals, HO2 + BrO → products (1) and DO2 + BrO → products (3), have been studied by the mass spectrometric discharge flow method at temperatures between 230 and 360 K and at a total pressure of 1 Torr of helium. The rate constant of reaction 1 as determined by monitoring either the HO2 or the BrO decay (in excess of BrO or HO2, respectively) is given by the Arrhenius expression k1 = (9.4 ± 2.3) × 10-12 exp[(345 ± 60)77] cm3 molecule-1 s'1, with k1 = (3.1 ± 0.8) × 10-11 cm3 molecule-1 s-1 at T = 298 K, where the uncertainties represent 95% confidence limits and include estimated systematic errors. The rate constant of reaction 3, measured under pseudo-first-order conditions in an excess of BrO, is k3 = (3.9 ± 1.2) × 10-12 exp[(410 ± 80)/T] cm3 molecule-1 s-1, with k3 = (1.6 ± 0.4) × 10-11 cm3 molecule-1 s-1 at T = 298 K, where the uncertainties represent 95% confidence limits and include estimated systematic errors. The value of k3 was measured for the first time, whereas the value of k1 was compared with those from previous studies. From the observation that no ozone formed among the products of the HO2 + BrO reaction, an upper limit was derived for the channel HO2 + BrO → HBr + O3 (1b) of reaction 1: k1b/k1 0.004 at T = 298 K. The implication of this result for stratospheric bromine partitioning is briefly discussed.
- Bedjanian, Yuri,Riffault, Véronique,Poulet, Gilles
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p. 3167 - 3175
(2007/10/03)
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- Kinetics and mechanism of the OH and OD reactions with BrO
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The kinetics and mechanism of the reactions OH + BrO → products (1) and OD + BrO → products (2) have been studied in the temperature ranges of 230-355 K and 230-320 K, respectively, and at total pressure of 1 Torr of helium using the discharge-flow mass s
- Bedjanian, Yuri,Riffault, Veronique,Le Bras, Georges,Poulet, Gilles
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p. 6154 - 6166
(2007/10/03)
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- Measurement of the rate coefficient for the reaction of OH with BrO
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We report the rate coefficient for the reaction OH + BrO → Products (1) at 298 K to be k1(298 K) = (4.5 ± 1.8) × 10-11 cm3 molecule-1 s-1. Reaction 1 was studied in an excess of BrO, generated in a flow tube, and measured via its UV-vis absorption. OH, produced by laser photolysis, was monitored by laserinduced fluorescence. Quoted uncertainties include estimated uncertainties in the BrO concentration and that due to the unavoidable concurrent reaction of OH with Br2. Our measured value of k1 is compared with that previously reported by Bogan et al.
- Gilles, Mary K.,McCabe, David C.,Burkholder, James B.,Ravishankara
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p. 5849 - 5853
(2007/10/03)
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- HCl yield from the OH + ClO reaction at temperatures between 218 and 298 K
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The yield of HCl from the OH + ClO reaction has been determined at 1 Torr total pressure by using the discharge-laminar-flow technique with resonance fluorescence, infrared diode laser spectrometry, and ultraviolet absorption spectrometry detection methods. A known amount of OH is added to a large excess of ClO and the reaction is allowed to go to completion. Under these conditions, the yield is just the ratio of [HCl] produced to initial [OH]. The yield or branching ratio measurement reduces to a measurement of two concentrations; knowledge of the total rate constant or of the branching rate constants is not required. The results are 9.0 ± 4.8% independent of temperature between 218 and 298 K. The errors given are two standard deviations. The results are also independent of the OH source: F + H2O or H + NO2. Interference from secondary chemistry is minimized by extrapolating a Plot of observed yields to zero initial [OH]. Numerical simulations are used only to check for interference from secondary chemistry and to validate the extrapolation procedure.
- Wang, Jin Jin,Keyser, Leon F.
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p. 6479 - 6489
(2007/10/03)
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- Uranyl-catalyzed chemiluminescent reaction of U4+ oxidation by dioxygen in aqueous HClO4 solution
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Chemiluminescence (CL) accompanying the reaction of U4+ with O2 in 0.0004-0.1 M HClO4 was studied. It was found that the electron-excited uranyl ion (UO22+)* is the CL emitter. The fact that the reaction rate and the CL yield increase as the solution acidity decreases was explained by different reactivities of the U4+aq aquaion and the products of its stepwise hydrolysis, UOH3+ and U(OH)22+, toward O2. Based on the results of analysis of the chain-radical mechanism of the reaction between U4+ and O2, it was concluded that transfer of an electron from the UO2+ ion to the oxidizing agent (a OH radical) is the most plausible elementary step of the reaction of (UO22+)* formation. It was found that the reaction rate, as well as the CL yield, increase substantially in the presence of uranyl ion. Catalytic action of UO22+ was explained by the formation of a UO22+ · UO2+ complex, which reduces the rate of the UO2+ disproportionation reaction (UO2+ is an intermediate of the reaction and is involved in chain propagation), and by regeneration of the active center, UO2+, in the reaction of UO22+ with U4+.
- Lotnik,Khamidullina,Kazakov
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p. 1512 - 1517
(2007/10/03)
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- Temperature Dependence of the HO2 + ClO Reaction. 1. Reaction Kinetics by Pulsed Photolysis-Ultraviolet Absorption and ab Initio Studies of the Potential Surface
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The kinetics of the HO2 + ClO reaction was studied using the flash photolysis/ultraviolet absorption technique over the temperature range 203-364 K and pressure range 50-700 Torr of N2. In contrast to previous work, the temperature dependence displayed linear Arrhenius behavior over the entire temperature range with the rate constant being described by the expression k(T) = 2.84 × 10-12 exp{(312 ± 60)/T} cm3 molecule-1 s-1. Ab initio calculations of intermediates and transition states have been carried out on the singlet and triplet potential energy surfaces. These calculations show that the reaction proceeds mainly through the ClO-HO2 complex on the triplet surface; however, collisionally stabilized HOOOCl formed on the singlet surface will possess an appreciable lifetime due to large barriers toward decomposition to HCl and HOCl. Termolecular rate calculations using ab initio parameters lead to a strong collision rate constant of ~5 × 10-32 cm6 molecule-2 s-1 for HOOOCl formation. This intermediate may be important under both laboratory and atmospheric conditions.
- Nickolaisen, Scott L.,Roehl, Coleen M.,Blakeley, Lisa K.,Friedl, Randall R.,Francisco, Joseph S.,Liu, Ruifeng,Sander, Stanley P.
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p. 308 - 319
(2007/10/03)
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- A novel catalyst of Cu-Bi-V-O complex in phenol hydroxylation with hydrogen peroxide
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A new catalyst of Cu-Bi-V-O complex oxide was hydrothermally synthesized in a Bi2O3-V2O5-CuO-H2O system, and its was found that this compound is very active for phenol hydroxylation by H2O2, which was comparable to titanium silicalite (TS-1). Investigation using the ESR spin-trapping technique on the catalyst indicated that Cu2+ species are major active sites, and hydroxyl radicals are the major active intermediates in phenol hydroxylation. The key factors for phenol conversion and product selectivity were reaction temperature, solvent, phenol/H2O2 molar ratio, reaction time, catalyst amount, and method of H2O2 addition.
- Sun, Jianmin,Meng, Xiangju,Shi, Yanhui,Wang, Runwei,Feng, Shouhua,Jiang, Dazhen,Xu, Ruren,Xiao, Feng-Shou
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p. 199 - 206
(2008/10/08)
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- The chloromethoxy radical: Kinetics of the reaction with O2 and the unimolecular elimination of HCl at 306 K
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The gas-phase kinetics of the CH2ClO radical, formed by flash photolysis of Cl2 in CH3Cl/O2/N2 mixtures, was investigated at 306 K and at total pressures from 5 to 35 Torr by time-resolved mass spectr
- Wu, Fuxiang,Carr, Robert W.
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- Formation of hydroxyl and hydroperoxy radicals in the gas-phase ozonolysis of ethene
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Ozonolysis of alkenes is thought be a significant source of free radicals (OH and HO2) in the atmosphere. Although studied for many years, the reaction mechanism and the product yields are still very much under discussion. We report measurements of the production of HO2 radicals from the reaction of O3 with ethene using matrix isolation and electron-spin-resonance spectroscopy (MIESR). Formation of OH radicals was established by conversion of OH to HO2 via reaction with CO. The OH yield is 20±2%, the HO2 yield is 39±3%. Our measurements suggest that the Criegee intermediate in the ground state is not a radical.
- Mihelcic,Heitlinger,Kley,Muesgen,Volz-Thomas
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p. 559 - 564
(2007/10/03)
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