- Intracavity laser absorption spectroscopy of HOCI overtones. I. the 3v1+2v2 band and numbers of vibrational states
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The near infrared high-resolution spectra of the a-type transitions of the weak 3v1+2v2 combination band of transient HO35(37)C1 at 12 600 cm-1 has been recorded in an ultrasensitive titaniunrsapphire intracavity laser absorption spectrometer (ICLAS). We report line assignments, new and refined anharmonicity parameters, and the spectroscopic constants for the excited rovibrational states of 3v1+2v2. The Fermi resonance perturbations in this five quanta region, where the internal energy of the molecule is already more than 2/3 of the dissociation energy E0, remain localized and they are the exception, while the extent of intermode mixing and thus intramolecular vibrational energy distribution (IVR) seems to be still small. A Dunham expansion is used for band origin predictions and representations of vibrational states N(E) of HO35C1 up to the dissociation threshold. The results are compared with harmonic and anharmonic numbers of states from a recently proposed stretch-bend coupling model.
- Abel, Bernd,Hamann, Hilmar H.,Kachanov, Alexander A.,Troe, Juergen
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- Heterogeneous Reactions of Chlorine Nitrate and Hydrogen Chloride on Type I Polar Stratospheric Clouds
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The heterogeneous reactions ClONO2 + HCl -> Cl2 + HNO3 (1) and ClONO2 + H2O -> HOCl + HNO3 (2) on vapor-deposited HNO3-H2O ice substrates have been investigated at 196 K by using a fast-flow reactor coupled with a quadrupole mass spectrometer.The reaction probability for (1) is 0.10 +/- 0.02 and independent of both the HNO3 and HCl concentrations in the substrate compositions studied.For (2), the reaction probability is approximately 1 * 10-5 near 53.8 wtpercent HNO3, the composition of pure nitric acid trihydrate (NAT), and is about 1 * 10-3 at 46 wtpercent HNO3.The sticking coefficient of HCl on these substrates was also found to be strong function of the substrate composition, ranging from about 2 * 10-5 at NAT composition to 6 * 10-3 at 45 wtpercent HNO3.The HNO3-H2O ice substrates were found to have large internal surface areas, and corrections for gas-phase diffusion within the porous ices were applied to observed loss rates.The large decrease in the HCl sticking coefficient and the reaction probability for (2) as the composition of pure NAT is approached from the water-enriched side can be semiquantitatively explained in terms of a simple two-solid-phase model.Finally, the relation of these results to the depletion of polar ozone is discussed.
- Leu, Ming-Taun,Moore, Steven B.,Keyser, Leon F.
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- Production and trapping of gaseous dimeric ClO: The infrared spectrum of chlorine peroxide (ClOOCl) in solid argon
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The dimeric ClO has been generated in a gaseous discharge-flow system at 220 K and 10-30 Torr by reacting atomic Cl with O3, ClOCl or OClO, and reacting atomic O with ClOCl or OClO, in a stream of Ar.The gas mixture in the flow tube was sampled through a pinhole and condensed on a CsI window maintained at 12 K.The infrared absorption spectrum of the matrix formed after 30-120 min deposition was then recorded.Absorption lines at 752.6, 649.8, and 647.6 cm-1 have been assigned to ClOOCl, and previous assignments for dimeric ClO seem to be in error.The results are inexcellent agreement with recent ab initio calculations.Under our experimental conditions, no other isomer of Cl2O2 was observed.
- Cheng, Bing-Ming,Lee, Yuan-Pern
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- The electrocatalytic activity of IrO2-Ta2O5 anode materials and electrolyzed oxidizing water preparation and sterilization effect
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Ti/IrO2-Ta2O5 anode electrocatalysts with different contents and preparation temperatures were prepared by thermal decomposition in this work. The crystallite characterization and morphology were examined via XRD and SEM. The electrochemical properties were examined via cyclic voltammetry (CV) in 0.5 M H2SO4 and linear sweep voltammetry (LSV) in saturated sodium chloride. Through the study of different series of Ti/IrO2-Ta2O5 anodes, we find that the preparation conditions have a great impact on the electrode catalytic activity. Experimental results indicate that the electrochemically active surface area is determined by the content and morphology of the anode coating. When the IrO2 content and the preparation temperature are 70% and 500 °C, the surface of the electrode is aggregated with segregated crystallite flower-like particles, which brings about the best electrode catalytic activity. The current density in the chlorine evolution reaction of IrO2-Ta2O5 (70% and 500 °C) is 0.4 A cm-2 in saturated sodium chloride. The properties and sterilization effect of EO water are closely related to the electrode catalytic activity. The higher the current density is in chlorine evolution, the higher the available chlorine and HClO content. When the IrO2 content is 70% and the preparation temperature is 500 °C, the maximum values of the killing logarithm value and killing rate are 3.01-3.05 and 99.9023-99.9109%, respectively. In addition, when the Ti substrate undergoes 40 minutes of activation treatment, the Ti/IrO2-Ta2O5 anodes have the highest stability.
- Ren, Zhandong,Quan, Shanshan,Gao, Jie,Li, Wenyang,Zhu, Yuchan,Liu, Ye,Chai, Bo,Wang, Yourong
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- Surface sensitive studies of the reactive uptake of chlorine nitrate on ice
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The reactive uptake of chlorine nitrate (ClONO2) on ice surfaces (ClONO2 + H2O → HOCl + HNO3) was studied with surface sensitivity using laser-induced thermal desorption (LITD) techniques. Thin films of vapor-deposited ice were exposed to ClONO2 vapor at substrate temperatures from 75 to 140 K. The reactive uptake of ClONO2 was directly measured by monitoring the hydrolysis reaction products, HOCl and HNO3, on the ice surface in real time. At low temperatures from 75 to 110 K, the HOCl coverage initially increased rapidly with ClONO2 exposure, indicating an efficient hydrolysis reaction. After longer ClONO2 exposures, the rate of HOCl production decreased and the HOCl reached a constant coverage. A reaction probability of γ = 0.03 was calculated for the reactive uptake of ClONO2 on ice and was independent of temperature from 75 to 110 K. At temperatures greater than 110 K, the reaction probability decreased with increasing temperature and reached a value of γ= 0.005 at 140 K. This decrease in the reaction probability with increasing substrate temperature is consistent with a precursor-mediated adsorption model. The good fits to the precursor-mediated adsorption model indicate that the ClONO2 hydrolysis reaction has a low activation barrier. The precursor-mediated adsorption model extrapolated to stratospheric temperatures predicts a reaction probability that is significantly lower than the accepted literature value of γ 0.3. This discrepancy may be caused by the higher pressures and the dynamic ice surface at stratospheric conditions that could enhance the reaction probability. The constant HOCl coverage reached after longer ClONO2 exposures is attributed to the poisoning of the ice surface by product HNO3. Calibrated HNO3 signals at 86 and 140 K revealed that the ClONO2 hydrolysis reaction is inhibited at a nitric acid coverage of 7.5 × 1014 molecules/cm2 or 1 monolayer. This coverage suggests that the hydrolysis reaction is limited to the surface or near-surface region of ice at these low temperatures.
- Berland,Tolbert,George
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- State selected unimolecular dissociation of HOCl near threshold: The 6vOH vibrational state
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The spectroscopy and unimolecular dissociation dynamics of HOCl are examined by accessing rotational resonances of the 6vOH vibrational level over the Ka=0-5 manifolds using overtone-overtone double resonance. The spectroscopic analysis indicates that state mixing between the zeroth-order bright O-H stretching overtone state, 6 0 0, and dark background vibrational levels is incomplete as the bright state couples to only a fraction of the available states. The coupling of 6 0 0 to a set of nearby dark states is mediated primarily by anharmonic coupling with the fourth-order vibrational resonance k1,233 playing a particularly important role through its ability to couple the 6 0 0 state directly to the 5 2 1 vibration and indirectly to the 4 4 2 vibration. The measured state-specific unimolecular dissociation rates for 6 0 0 show large fluctuations with J and Ka and are substantially slower than that expected on the basis of statistical theory. The rate fluctuations are interpreted on the basis of spectroscopic data which suggest that the fluctuations arise as a result of variation in state mixing as different dark vibrational states come in and out of resonance with the bright state for different values of J and Ka.
- Dutton, Gregory,Barnes, Rhett James,Sinha, Amitabha
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- Kinetic mechanism of ClONO2 uptake on polycrystalline film of NaCl
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Kinetic studies and the mechanism determination of ClONO2 uptake on polycrystalline NaCl were carried out using a coated-insert flow tube reactor combined with high-resolution, low-energy electron-impact mass spectrometer under the following conditions: p =1-2 Torr, linear flow velocity v = 3.5-75 m s-1, T = 293 and 387 K, [ClONO2] = (0.5-25) × 1012 molecules cm-3. The salt was deposited as a film from nonsaturated aqueous solution on the sliding rod. The temporal dependences of the uptake coefficient and the partial uptake coefficients leading to a formation of the prime Cl2 and HOCl products were measured for different ClONO2 concentrations. These dependences are established to be described by γ = γ0 exp(-t/τ) + γs, γ0.s-1 = a0.S + b0.s[ClONO2]. In the framework of the proposed kinetic model, the data are explained and the main elementary kinetic parameters of the uptake are evaluated. The model is based on a combination of Langmuir adsorption, formation of surface complexes on initial active sites, Z ch, followed by their unimolecular decomposition. Decomposition is proposed to proceed concurrently in two channels, one of which is a released surface site that conserves the properties of the initial site. In the other channel, the initial Zch transforms into Zph followed by steady-state uptake and reproduction of final Zph. The model gives an analytical expression for experimental parameters γ0, γs, and τ in terms of elementary rate constants and the reactant volume concentration. The final objective of the proposed model is the extrapolation of γ0, γs, and r parameters to real tropospheric conditions.
- Zelenov,Aparina,Kashtanov,Shestakov,Gershenzon
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- Studies of reactions of importance in the stratosphere. IV. Rate constant for the reaction Cl + HOCl--> HCl + ClO over the temperature range 243-365 K
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The title reaction was studied over the temperature range 243-365 K using the discharge flow technique with mass spectrometry for detection.The rate constant was measured by detecting the loss of HOCl in the presence of a large excess of chlorine atoms.The resulting temperature dependent rate constant is given by k = (3.0 +/- 0.5) * 10-12exp cm3 molecule-1 s-1, where the stated errors include our estimate of the maximum possible systematic error.This reaction becomes a significant pathway to HCl in the stratosphere when the total ClX exceeds 10 ppbv.Upper limits for rate constants for the reactions HOCl + NO --> products and HOCl + O3 -> products at 300 K were established to be 1.0 * 10-17 and 4.0 * 10-16 cm3 molecule-1 s-1, respectively.
- Cook, Jac-E L.,Ennis, Christine A.,Leck, Thomas J.,Birks, John W.
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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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- The hydrolysis of chlorine nitrate on ice is autocatalytic
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A key chemical reaction in stratospheric ozone depletion is the reaction of chlorine nitrate (ClONO2) with water. This reaction is known to be catalyzed in the presence of ice particles found in polar stratospheric clouds (PSCs). However, the mechanism and time scale of the reaction, and the role of the ice surface, are not well understood. This surface second harmonic generation study shows that the submonolayer ClONO2 hydrolysis on basal ice (Ih) surfaces at 185 K occurs autocatalytically, with the product molecule HOCl acting as the autocatalyst. The other product, HNO3, acts to delay the reaction. The hydrolysis reaction is surprisingly slow, with induction times that range from 100 to 1000 s, depending upon how much reactant is initially present. It is proposed that the ice surface serves as a reservoir, enabling the reaction to be acid catalyzed.
- Geiger, Franz M.,Pibel, Charles D.,Hicks, Janice M.
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- Rate constants for reactions between iodine- and chlorine-containing species: A detailed mechanism of the chlorine dioxide/chlorite-iodide reaction
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The chlorite-iodide reaction is unusual because it is substrate-inhibited and autocatalytic. Because analytically pure ClO2- ion is not easily prepared, it was generated in situ from the rapid reaction between ClO2 and I-. The resulting overall reaction is multiphasic, consisting of four separable parts. Sequentially, beginning with mixing, these parts are the (a) chlorine dioxide-iodide, (b) chlorine(III)-iodide, (c) chlorine(III)-iodine, and (d) hypoiodous and iodous acid disproportionation reactions. The overall reaction has been studied experimentally and by computer simulation by breaking it down into a set of kinetically active subsystems and three rapidly established equilibria: protonations of chlorite and HOI and formation of I3-. The subsystems whose kinetics and stoichiometries were experimentally measured, remeasured, or which were previously experimentally measured include oxidation of iodine(-1,0,+1,+3) by chlorine(0,+1,+3), oxidation of I- by HIO2, and disproportionation of HOI and HIO2. The final mechanism and rate constants of the overall reaction and of its subsystems were determined by sensitivity analysis and parameter fitting of differential equation systems. Rate constants determined for simpler reactions were fixed in the more complex systems. A 13-step model with the three above-mentioned rapid equilibria fits the overall reaction and all of its subsystems over the range [I-]0 -3 M, [ClO2-]0 -3 M, [I-]0/[ClO2-]0 = 3-5, pH = 1-3.5, and 25°C. The derived model with all experimentally determined rate and equilibrium constants fits both the overall reaction and all of its subsystems within 1% relative accuracy.
- Lengyel,Li,Kustin,Epstein
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- Catalase prevents myeloperoxidase self-destruction in response to oxidative stress
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Catalase (CAT) and myeloperoxiase (MPO) are heme-containing enzymes that have attracted attention for their role in the etiology of numerous respiratory disorders such as cystic fibrosis, bronchial asthma, and acute hypoxemic respiratory failure. However, information regarding the interrelationship and competition between the two enzymes, free iron accumulation, and decreased levels of non-enzymatic antioxidants at sites of inflammation is still lacking. Myeloperoxidase catalyzes the generation of hypochlorous acid (HOCl) from the reaction of hydrogen peroxide (H2O2) and chloride (Cl?). Self-generated HOCl has recently been proposed to auto-inhibit MPO through a mechanism that involves MPO heme destruction. Here, we investigate the interplay of MPO, HOCl, and CAT during catalysis, and explore the crucial role of MPO inhibitors and HOCl scavengers in protecting the catalytic site from protein modification of both enzymes against oxidative damage mediated by HOCl. We showed that CAT not only competes with MPO for H2O2 but also scavenges HOCl. The protective role provided by CAT versus the damaging effect provided by HOCl depends in part on the ratio between MPO/CAT and the affinity of the enzymes towards H2O2 versus HOCl. The severity of such damaging effects mainly depends on the ratio of HOCl to enzyme heme content. In addition to its effect in mediating protein modification and aggregation, HOCl oxidatively destroys the catalytic sites of the enzymes, which contain porphyrin rings and iron. Thus, modulation of MPO/CAT activities may be a fundamental feature of catalysis, and functions to down-regulate HOCl synthesis and prevent hemoprotein heme destruction and/or protein modification.
- Ali, Iyad,Khan, Sana N.,Chatzicharalampous, Charalampos,Bai, David,Abu-Soud, Husam M.
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- Reaction of ClONO2 with H2O and HCl in sulfuric acid and HNO3/H2SO4/H2O mixtures
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Measurements of the reaction probabilities (γ) for ClONO2 onto sulfuric acid solutions at 200-270 K are described. ClONO2 uptake due to reaction with H2O and with HCl in H2SO4 solutions (45-55 wt percent) was investigated at 203-205 K. ClONO2 hydrolysis was also investigated on 36.5, 40, and 75 wt percent sulfuric acid solutions over a range of temperatures. The measured γ are generally in good agreement with previously reported values. In addition, the solubility of HCl was determined for 45 and 50 wt percent sulfuric acid from 200 to 225 K. The uptake of ClONO2 onto small sulfuric acid particles was studied resulting in a lower limit to the sticking coefficient of 0.5. ClONO2 reaction probabilities were also measured on H2SO4 solutions containing significant amounts of HNO3. In opposition to previous reports, HNO3 was found to have a significant effect on γ for ClONO2: it is as low as one-half of that expected for the comparable HNO3-free solutions. The measured γ on sulfuric acid solutions at 203 ± 2 K are discussed in terms of solubility, diffusivity, and bulk and surface reactions. Within this framework, the measured γ were fit as a function of H2SO4 and HCl content, thus allowing for the measurements to be extrapolated to atmospheric conditions.
- Hanson, David R.
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- Thermodynamic and kinetic properties of the reaction Cl + O2 + MClOO + M in the range 160-300 K and 1-1000 bar
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The reaction Cl + O2 + MClOO + M was studied by laser flash photolysis in the bath gases M = He, Ar, N2, and O2 over the temperature range 160-300 K and the pressure range 1-1000 bar.UV absorptions of ClOO were monitored, a maximum absorption cross section of ?(248 nm) = 3.4*10-17 cm2 was determined.An expression for the equilibrium constant Kp = 5.3*10-6 exp( + 23.4 kJ mol-1/RT) bar-1 was derived between 180 and 300 K, which, by a third law analysis, yields Η0 deg = -20.2 +/- 0.2 kJ mol-1.Limiting low pressure rate coefficients for Cl + O2 recombination of k0 = 8.8*10-34 (T/300 K)-3.0, k0 = 1.6*10-33 (T/300 K)-2.9, k0 = 1.4*10-33 (T/300 K)-3.9 cm6 s-1 were obtained over the range 160-260 K, as well as k0 (160 K) = 2.2*10-32 cm6 s-1.Rate constants for the reactions Cl + ClOO -> Cl2 + O2 or 2ClO, ClOO + ClOO -> products, and ClOO + Cl2 -> Cl2O + ClO were also derived.The recombination Cl + O2( + M) -> ClOO( + M) at pressures above 10 bar shows a transition to a high pressure plateau and, at pressures above 200 bar, to diffusion control.It is suggested that, like O + O2( + M) -> O3( + M), the reaction is governed by a radical complex mechanism.
- Baer, S.,Hippler, H.,Rahn, R.,Siefke, M.,Seitzinger, N.,Troe, J.
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- Myeloperoxidase-mediated oxidation of edaravone produces an apparent non-toxic free radical metabolite and modulates hydrogen peroxide-mediated cytotoxicity in HL-60?cells
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Edaravone is considered to be a potent antioxidant drug known to scavenge free radical species and prevent free radical-induced lipid peroxidation. In this study, we investigated the effect of edaravone on the myeloperoxidase (MPO) activity, an enzyme res
- Suh, Lindsey Y.K.,Babu, Dinesh,Tonoyan, Lusine,Reiz, Béla,Whittal, Randy,Tabatabaei-Dakhili, S. Amirhossein,Morgan, Andrew G.,Velázquez-Martínez, Carlos A.,Siraki, Arno G.
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- Heterogeneous Reactions of ClONO2, HCl, and HOCl on Liquid Sulfuric Acid Surfaces
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The heterogeneous reactions of ClONO2 + H2O -> HNO3 + HOCl (1), ClONO2 + HCl -> Cl2 + HNO3 (2), and HOCl + HCl -> Cl2 + H2O (3) on liquid sulfuric acid surfaces have been studied using a fast flow reactor coupled to a quadrupole mass spectrometer.The main objectives of the study are to investigate (a) the temperature dependence of these reactions at a fixed H2O partial pressure typical of the lower stratosphere (that is, by changing temperature at a constant water partial pressure, typical of the lower stratosphere that is by changing temperature at a constant water partial pressure, the H2SO4 content of the surfaces is also changed), (b) the relative importance or competition between reactions 1 and 2, and (c) the effect of HNO3 on the reaction probabilities due to the formation of a H2SO4/HNO3/H2O tern m.The measurements show that all the reactions depend markedly on temperature at a fixed H2O partial pressure: they proceed efficiently at temperatures near 200 K and much slower at temperatures near 220 K.The reaction probability (γ1) for ClONO2 hydrolysis approaches 0.01 at temperatures below 200 K, whereas the values for γ2 and γ3 are on the order of a few tenths at 200 K.Although detailed mechanisms for these reactions are still unknown, the present data indicate that the competition between ClONO2 hydrolysis and ClONO2 reaction with HCl may depend on temperature (or H2SO4 wt percent): in the presence of gaseous HCl at stratospheric concentrations, reaction 2 is dominant at lower temperatures (200 K), but reaction 1 becomes important at temperatures above 210 K.Furthermore, reaction probability measurements performed on the H2SO4/HNO3/H2O ternary solutions do not exhibit noticeable deviation from those performed on the H2SO4/H2O binary system, suggesting little effect of HNO3 in sulfate aerosols on the ClONO2 and HOCl reactions with HCL. The results reveal that significant reductions in the chlorine-containing reservoir species (such as ClONO2 and HCl) can take place on stratospheric sulfate aerosols at high latitudes in winter and early spring, even at temperatures too warm for polar stratospheric clouds (PSCs) to form or in regions where nucleation of PSCs is sparse.This is particularly true under elevated sulfuric acid loading, such as that after the eruption of Mt.Pinatubo.Comparisons between our results and those presently available have also been made.
- Zhang, Renyi,Leu, Ming-Taun,Keyser, Leon F.
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- Photolysis of HOCl at 248 nm in a Supersonic Molecular Beam: Laser-induced Fluorescence Spectra of OH
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The nascent OH rotational distribution has been observed following the 248 nm photolysis of HOCl in a supersonic molecular beam.A strong preference for the population of the OH 2Π2/3 spin state is found and a significant deviation fr
- Bell, Andrew J.,Pardon, Patrick R.,Hickman, Christopher G.,Frey, Jeremy G.
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- Heterogeneous Interactions of ClONO2 and HCl with Sulfuric Acid Tetrahydrate: Implications for the Stratosphere
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The reaction probabilities for ClONO2+H2O -> HOCl+HNO3 (1) and ClONO2+HCl -> Cl2+HNO3 (2) have been investigated on sulfuric acid tetrahydrate (SAT, H2SO4*4H2O) surfaces at temperatures between 190 and 230 K and at reactant concentrations that are typical in the lower stratosphere, using a fast-flow reactor coupled to a quadrupole mass spectrometer.The results indicate that the reaction probabilities as well as HCl uptake depend strongly on the thermodynamic state of SAT surface: they decrease significantly with decreasing H2O partial pressure at a given temperature, and decrease with increasing temperature at a given H2O partial pressure, as the SAT changes from the H2O-rich form to the H2SO4-rich form.For H2O-rich SAT at 195 K γ1 ca. 0.01 and γ2 >/= 0.1, whereas the values for H2SO4-rich SAT decrease by more than 2 orders of magnitude.At low concentrations of HCl, close to those found in the stratosphere, the amount of HCl taken up by H2O-rich SAT films corresponds to a coverage of the order of a tenth of a monolayer (ca. 1E14 molecules cm-2); H2SO4-rich SAT films take up 2 orders of magnitude less HCl (-2).Substantial HCl uptake at high HCl concentrations is also observed, as a result of surface melting.The data reveal that frozen stratospheric sulfate aerosols may an important role in chlorine activation in the winter polar stratosphere via processes similar to those occurring on the surfacees of polar stratospheric cloud particles.
- Zhang, Renyi,Jayne, John T.,Molina, Mario J.
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- ESR spectrum of ClO (2Π3/2) isolated in a CO2 matrix
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Upon isolation of ClO in a CO2 matrix at 10 K, a highly anisotropic ESR spectrum is observed which is attributed to ClO.This might be the first observation of a neutral radical with a 2Π ground state in a nonpolar matrix.Some of the structure discernible on the spectrum at 10 K may be related to ClO at different trapping sites.After annealing the sample at T > 45 K, the radical concentration diminishes and the g peak of the most prominent site splits into four peaks which may correspond to the hyperfine splitting of ClO.The spectrum can be explained by the following g and A tensors, gx = 1.889, gy = 1.899, gz = 2.66 and Ax = 111 MHz, Ay 20 MHz, Az 55 MHz.In a simple crystal field model these values are compared with molecular parameters of ClO deduced from gas phase spectra.
- Trainer, M.,Helten, M.,Knapska, D.
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- State selected unimolecular dissociation of HOCl
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The unimolecular decomposition of HOCl is investigated by exciting the molecule to the region of the sixth overtone of its OH stretching vibration (7νOH) using overtone-overtone double resonance.The excitation scheme is sufficiently selective to allow preparation of a single angular momentum quantum state within the 7νOH vibrational manifold lying ca. 2500 cm-1 above the dissociation limit.From the measured linewidths associated with the rotational features appearing in the action spectrum, we obtain an upper limit estimate for the dissociation rate of kuni9 s-1 which is substantially slower than that expected on the basis of RRKM theory.The nascent OH fragment product state distribution exhibit strong oscillations which depend on the rotational quantum numbers of the parent HOCl molecule.From the measured energy release associated with the OH fragment, the heat of formation of HOCl is estimated to be ΔH00(0K)=-16.7+/-0.6 kcal/mol.
- Barnes, Rhett James,Sinha, Amitabha
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- Uptake and reaction of ClONO2 on NaCl and synthetic sea salt
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The uptake and reaction of chlorine nitrate (ClONO2) on NaCl and synthetic sea salt (SSS) powders was studied at 298 K using a Knudsen cell interfaced to a quadrupole mass spectrometer. A time-dependent uptake coefficient was observed, with a large initial uptake coefficient measured for most samples of γinit > 0.1, followed by a smaller and slowly declining uptake coefficient at longer reaction times. This behavior is shown to be consistent with uptake into, and reaction in, water on the salt surface. The steady-state uptake coefficient on NaCl was invariant over a range of ClONO2 concentrations from 1012 to 1013 molecules cm-3 but was dependent on the number of salt particle layers in a manner consistent with approximately two layers of particles being available for reaction. The results of experiments using monolayers and sub-monolayers of salts, where the available reactive surface is known, give an uptake coefficient at longer times after the rapid initial uptake for ClONO2 on NaCl of γt = (6.5 ± 3.0) × 10-3 (2σ). The larger uptake coefficient obtained initially compared to longer reaction times helps to reconcile different values reported earlier by other research groups for this reaction. The uptake coefficient on SSS, which holds more water, is much larger than that for NaCl, with γinit = (0.42-0.42+0.46) and γt = (0.16-0.16+0.20 (2σ). At the higher uptake coefficients measured for SSS, this reaction could be a significant source of Cl2 in the marine boundary layer if chlorine nitrate is available at a constant concentration of ~5 ppt.
- Gebel, Michael E.,Finlayson-Pitts, Barbara J.
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- AQUEOUS SOLUTION HAVING HYPOCHLOROUS ACID AS MAIN COMPONENT
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PROBLEM TO BE SOLVED: To provide a solution having hypochlorous acid with improved storage stability as a main component. SOLUTION: The present invention discloses an aqueous solution having hypochlorous acid as a main component in which 40 mol% or more of the total sum of chlorine in the aqueous solution is chlorine of hypochlorous acid: particularly, an aqueous solution having hypochlorous acid as a main component in which 40 mol% or more of the total sum of chlorine in the aqueous solution is chlorine of hypochlorous acid, in which the total sum of alkali metal ions and alkaline earth metal ions is less than 1 mEq/L, and in which the total sum of negative ions in the aqueous solution other than hypochlorous acid is less than 10 mg/L, and which suppress metal corrosion. SELECTED DRAWING: None COPYRIGHT: (C)2022,JPOandINPIT
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Paragraph 0038-0048
(2021/11/02)
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- Melatonin prevents hypochlorous acid-mediated cyanocobalamin destruction and cyanogen chloride generation
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Hypochlorous acid (HOCl) is a potent cytotoxic oxidant generated by the enzyme myeloperoxidase (MPO) in the presence of hydrogen peroxide (H2O2) and chloride (Cl?). Elevated levels of HOCl play an important role in various pathological conditions through oxidative modification of several biomolecules. Recently, we have highlighted the ability of HOCl to mediate the destruction of the metal-ion derivatives of tetrapyrrole macrocyclic rings such as hemoproteins and vitamin B12 (VB12) derivatives. Destruction of cyanocobalamin, a common pharmacological form of VB12 mediated by HOCl, results in the generation of toxic molecular products such as chlorinated derivatives, corrin ring cleavage products, the toxic blood agents cyanide (CN?) and cyanogen chloride (CNCl), and redox-active free cobalt. Here, we show that melatonin prevents HOCl-mediated cyanocobalamin destruction, using a combination of UV-Vis spectrophotometry, high-performance liquid chromatography analysis, and colorimetric CNCl assay. Identification of several melatonin oxidation products suggests that the protective role of melatonin against HOCl-mediated cyanocobalamin destruction and subsequent CNCl generation is at the expense of melatonin oxidation. Collectively, this work highlights that, in addition to acting as an antioxidant and as a MPO inhibitor, melatonin can also prevent VB12 deficiency in inflammatory conditions such as cardiovascular and neurodegenerative diseases, among many others.
- Jeelani, Roohi,Maitra, Dhiman,Chatzicharalampous, Charalampos,Najeemuddin, Syed,Morris, Robert T.,Abu-Soud, Husam M.
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- COMPOSITIONS OF HYPOCHLOROUS ACID(HOCl) AND METHODS OF MANUFACTURE THEREOF
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The invention generally relates to compositions of hypochlorous acid (HOCl) and methods of manufacture thereof. In certain aspects, the invention provides air-free compositions of HOCl. In other aspects, the invention provides methods of making HOCl that involve mixing together in water in an air-free environment, a compound that generates a proton (H+) in water and a compound that generates a hypochlorite anion (OCl?) in water to thereby produce air-free hypochlorous acid.
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Paragraph 0029-0032
(2015/06/10)
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- Photoreduction of Pt(IV) halo-hydroxo complexes: Possible hypohalous acid elimination
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Concentrated hydrogen peroxide addition to trans-Pt(PEt3) 2Cl(R) [1 (R = 9-phenanthryl), 2 (R = 4-trifluoromethylphenyl)] yields hydroxo-hydroperoxo complexes trans-Pt(PEt3) 2(Cl)(OOH)(OH)(R) [5 (R = 9-phenanthryl), 4 (R = 4- trifluoromethylphenyl)], where the hydroperoxo ligand is trans to R. Complex 5 is unstable and reacts with solvent CH2Cl2 to give trans,cis-Pt(PEt3)2(Cl)2(OH)(9-phenanthryl) (3). Treatment of 4 with HCl yields analogous trans,cis-Pt(PEt3) 2(Cl)2(OH)(4-trifluoromethylphenyl) (6) and HBr gives trans-Pt(PEt3)2(Br)(Cl)(OH)(4-trifluoromethylphenyl) (7), where the Br and 4-trifluoromethylphenyl ligands are trans. Photolysis of 3 or 6 at 313 or 380 nm causes reduction to trans-Pt(PEt3)2Cl(R) (1 or 2, respectively). Expected coproduct HOCl is not detected, but authentic solutions of HOCl are shown to decompose under the reaction conditions. Chlorobenzene and other unidentified products that oxidize PPh3 to OPPh3 are detected in photolyzed benzene solutions. Photolysis of 3 or 6 in the presence of 2,3-dimethyl-2-butene (TME) yields the chlorohydrin (2-chloro-2,3-dimethyl-3-butanol), 3-chloro-2,3-dimethyl-1-butene, and acetone, all expected products from HOCl trapping, but additional oxidation products are also observed. Photolysis of mixed chloro-bromo complex 7 with TME yields the bromohydrin (2-bromo-2,3-dimethyl-3-butanol) and 2, consistent with cis-elimination of HOBr. Computational results (TDDFT and DFT) and photochemistry of related complexes suggest a dissociative triplet excited state reaction pathway and that HOCl elimination may occur by an incipient hydroxo radical abstraction of an adjacent halogen atom, but a pathway involving hydroxo radical reaction with solvent or TME to generate a carbon-based radical followed by halogen abstraction from Pt cannot be eliminated.
- Wickramasinghe, Lasantha A.,Sharp, Paul R.
-
p. 1430 - 1442
(2014/03/21)
-
- SOLUTION CONTAINING HYPOCHLOROUS ACID AND METHODS OF USING SAME
-
The present invention relates to low pH antimicrobial solutions comprising hypochlorous acid, water, and, optionally, a buffer. The inventive low pH antimicrobial solutions have a pH from about 4 to about 6 and are useful for treating impaired or damaged tissue and for disinfecting surfaces. Chemical processes for the production of the low pH antimicrobial solutions are also provided wherein chlorine gas is added to a buffer solution containing a buffering agent and water. The present invention also provides an electrochemical process for the production of the low pH antimicrobial solutions.
- -
-
Page/Page column 13
(2010/12/31)
-
- Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation
-
The photodissociation dynamics of ClONO2 at 235 nm has been reinvestigated using velocity map ion imaging. We report branching ratios for the Cl + NO3 and ClO + NO2 channels to be 0.49:0.51 with anisotropy parameters of β
- Kim, Hahkjoon,Greenwald, Erin E.,North, Simon W.
-
-
- METHODS AND COMPOSITIONS FOR THE TREATMENT OF PAIN
-
The invention features methods, kits, and compositions for the treatment of pain.
- -
-
Page/Page column 25
(2008/12/07)
-
- Effect of chloride ion on the kinetics and mechanism of the reaction between chlorite ion and hypochlorous acid
-
The effect of chloride ion on the chlorine dioxide formation in the ClO2--HOCl reaction was studied by following ?ClO2 concentration spectrophotometrically at pH 5-6 in 0.5 M sodium acetate. On the basis of the earlier experimental data collected without initially added chloride and on new experiments, the earlier kinetic model was modified and extended to interpret the two series of experiments together. It was found that the chloride ion significantly increases the initial rate of ?ClO2 formation. At the same time, the ?ClO2 yield is increased in HOCl but decreased in ClO2- excess by the increase of the chloride ion concentration. The two-step hydrolysis of dissolved chlorine through Cl2 + H2O ? Cl 2OH- + H+ and Cl2OH- ? HOCl + Cl- and the increased reactivity of Cl 2OH- compared to HOCl are proposed to explain these phenomena. It is reinforced that the hydrolysis of the transient Cl 2O2 takes place through a HOCl-catalyzed step instead of the spontaneous hydrolysis. A seven-step kinetic model with six rate parameters (constants and/or ratio of constants) is proposed on the basis of the rigorous least-squares fitting of the parameters simultaneously to 129 absorbance versus time curves measured up to ~90% conversion. The advantage of this method of evaluation is briefly outlined.
- Kormanyos, Balazs,Nagypal, Istvan,Peintler, Gabor,Horvath, Attila K.
-
p. 7914 - 7920
(2009/02/08)
-
- Kinetic study of the ClOO + NO reaction using cavity ring-down spectroscopy
-
Cavity ring-down spectroscopy was used to study the reaction of ClOO with NO in 50-150 Torr total pressure of O2/N2 diluent at 205-243 K. A value of k(ClOO+NO) = (4.5 ± 0.9) × 10-11 cm3 molecule-1 s-1 at 213 K was determined (quoted uncertainties are two standard deviations). The yield of NO2 in the ClOO + NO reaction was 0.18 ± 0.02 at 213 K and 0.15 ± 0.02 at 223 K. An upper limit of k(ClOO+Cl2) -14 cm3 molecule-1 s-1 was established at 213 K. Results are discussed with respect to the atmospheric chemistry of ClOO and other peroxy radicals.
- Enami, Shinichi,Hoshino, Yosuke,Ito, Yuki,Hashimoto, Satoshi,Kawasaki, Masahiro,Wallington, Timothy J.
-
p. 3546 - 3551
(2008/10/09)
-
- Reactions of POxCly-ions with H and H 2 from 298 to 500 K
-
Rate constants and product branching ratios for POxCl y-ions reacting with H and H2 were measured in a selected ion flow tube (SIFT) from 298 to 500 K. PO2Cl-, PO2Cl2-, POCl2-, and POCl3- were all unreactive with H2, having a rate constant with an upper limit of -12 cm 3 s-1. PC2Cl2- did not react with H atoms either, having a similar rate constant limit of -12 cm3 s-1. The rate constants for PO 2Cl-, POCl2-, and POCl 3- reacting with H showed no temperature dependence over the limited range of 298-500 K and were approximately 10-20% of the collision rate constant Cl abstraction by H to form HCl was the predominant product channel for PO2Cl-, POCl2-, and POCl3-, with a small amount of Cl- observed from POCl2- + H. Reactions of O2 and O 3 with the POCl- products ions from the reaction of POCl2- + H were observed to yield predominantly PO 3- and PO2-, respectively. POCl - reacted with C2 and O3 with rate constants of 8.9 ± 1.1 × 10-11 and 5.2 ± 3.3 × 10 -10 cm3 s-1, respectively. No associative electron detachment in the reactions with H atoms was observed with any of the reactant ions; however, detachment was observed with a PO- secondary product ion at high H atom concentrations. Results of new G3 theoretical calculations of optimized geometries and energies for the products observed are discussed.
- Midey, Anthony J.,Miller, Thomas M.,Morris, Robert A.,Viggiano
-
p. 2559 - 2563
(2008/03/12)
-
- Autocatalysis and self-inhibition: Coupled kinetic phenomena in the chlorite-tetrathionate reaction
-
The initial rate of formation of chlorine dioxide in the chlorite-tetrathionate reaction changes in an unusual fashion. The formal kinetic order of both reactants varies over a very wide range. Moreover, chlorite ion behaves not just as a simple reactant, but also as a self-inhibitor. A five-step scheme, derived from an eight-step mechanism, is proposed in which the autocatalytic formation of HOCl plays a central role in accounting for this kinetic behavior. Copyright
- Horvath, Attila K.,Nagypal, Istvan,Peintler, Gabor,Epstein, Irving R.
-
p. 6246 - 6247
(2007/10/03)
-
- Reaction kinetics of PO2Cl-, PO2Cl 2-, POCl2- and POCl3 - with O2 and O3 from 163 to 400 K
-
Rate constants and product ion branching fractions for the gas-phase reactions of O2 and O3 with the anions (a) PO 2Cl-, (b) POCl3-, (c) POCl 2-, and (d) PO2Cl2- were measured in a selected-ion flow tube (SIFT). The kinetics were measured at temperatures of 163-400 K and a He pressure of 0.4 Torr. Only PO 2Cl- reacts with O2 to a measurable extent, having k(163-400 K) = 1.1 × 10-8(T/K)-1.0 cm 3 molecule-1 s-1, while O3 reacts with all of the anions except PO2Cl2-. The fitted rate constant expressions for the O3 reaction with anions a-c are as follows: ka(163-400 K) = 3.5 × 10-6(T/K) -1.6, kb(163-400 K) = 4.0 × 10 -7(T/K)-1.2, and kc(163-400 K) = 3.7 × 10-7(T/K)-1.4 cm3 molecule-1 s -1. Calculations were performed at the G3 level of theory to obtain optimized geometries, energies, and electron affinities (EAs) of the reactant and product species, as well as to determine the reaction thermochemistry to help understand the experimental results. The POxCly - anions that have lower electron binding energies (eBE) and higher spin multiplicities are more reactive. The doublets are more labile than the singlets. How the extra electron density is distributed in the anion does not predict the observed reactivity of the ion. The reactions of PO 2Cl- with O2 and O3 yield predominantly PO3- and PO4-. The reaction of POCl2- with O3 yields mostly Cl- and PO2Cl2-, while the POCl 3- reaction with O3 yields mostly O 3- and PO2Cl2-.
- Fernandez, Abel I.,Midey, Anthony J.,Miller, Thomas M.,Viggiano
-
p. 9120 - 9125
(2008/10/09)
-
- Femtosecond pump-probe studies of dichlorine monoxide in solution
-
The first femtosecond pump-probe studies of ClOCl photochemistry in solution are presented. Following 266-nm photoexcitation of ClOCl dissolved in perfluorohexane, the resulting evolution in optical density is monitored at seven wavelengths ranging from 266 to 400 nm. A depletion in optical density consistent with ground-state ClOCl photolysis is observed, followed by increases in optical density at 266 and 315 nm assigned to the production of ClO and ClClO, respectively. Kinetic analysis of the temporal evolution in optical density establishes that photoproduct appearance occurs on the ~10-ps time scale. Later time decay of the optical density at 315 nm is mirrored by a corresponding increase in optical density at 266 nm consistent with thermal decomposition of ClClO to produce ClO and Cl on the ~100-ps time scale. The quantum yields for photoproduct formation are determined through analysis of the absolute change in optical density. This analysis establishes that the quantum yields for ClClO and ClO production are 0.4 ±0.1 and 0.6 ± 0.1, respectively. Finally, the observation of ClClO production following ClOCl photoexcitation is similar to the behavior observed for chlorine dioxide (OClO) suggesting that photoisomerization is a general feature of halooxide reactivity in solution.
- Cooksey, Catherine C.,Reid, Philip J.
-
p. 5508 - 5514
(2007/10/03)
-
- Kinetics and mechanisms of aqueous chlorine reactions with chlorite ion in the presence of chloride ion and acetic acid/acetate buffer
-
The kinetics and mechanism of the reaction between Cl2 and CIO2- are studied in acetate buffer by stopped-flow spectrometric observation of CIO2 formation. The reaction is first-order in [CI2] and [CIO2-], with a rate constant of k1 = (5.7 ± 0.2) × 105 M-1 s-1 at 25.0 °C. Nucleophilic attack by CIO2- on CI2, with CI+ transfer to form CIOCIO and CI-, is proposed as the rate-determining step. A possible two-step electron-transfer mechanism for CI2 and CIO2- is refuted by the lack of CIO2 suppression. The yield Of CIO2 is much less than 100%, due to the rapid reactions of the metastable CIOCIO intermediate via two competing pathways. In one path, CIOCIO reacts with CIO2- to form 2CIO2 and CI-, while in the other path it hydrolyzes to give CIO3- and CI-. The observed rate constant also is affected by acetate-assisted hydrolysis of CI2. The rate of CI2 loss is suppressed as the concentration of CI- increases, due to the formation of CI3-. In excess CIO2-, a much slower formation of CIO2 is observed after the initial CI2 reaction, due to the presence of HOCI, which reacts with H+ and CI- to re-form steady-state levels of CI2.
- Nicoson, Jeffrey S.,Margerum, Dale W.
-
p. 342 - 347
(2008/10/08)
-
- Matrix infrared spectroscopic studies of the photo-dissociation at 266 nm of C1NO2 and of C1ONO
-
Detailed infrared spectroscopic studies of the photo-dissociation at 266 nm of C1NO2 trapped in argon matrices with subsequent experiments conducted with a xenon lamp at λ > 360 nm are reported. Formation of cis and trans C1ONO in equilibrium with C1NO2 is observed after irradiation at 266 nm. λ > 360 nm the transformation of trans C1ONO into cis C1ONO occurs. On prolonged photolysis at 266 nm, C1ONO dissociates into C1ON and O(1D) atom and into C10 + NO as evidenced in reactive matrices (solid oxygen and nitrogen).
- Coanga,Schriver-Mazzuoli,Schriver,Dahoo
-
p. 309 - 320
(2008/10/08)
-
- Photoionization of the primary photoproducts of A(2∏)-excited CIO
-
Photoionization study of the primary photofragments of chlorine monoxide (ClO) is presented. The primary photolysis products and the non-photolyzed ClO are probed by monochromatic, time-correlated vacuum-ultraviolet radiation from a laser produced plasma source. The results are compared to additional photolysis work on molecular chlorine.
- Flesch,Plenge,Kuehl,Klusmann,Ruehl
-
p. 9663 - 9670
(2007/10/03)
-
- Rate constant measurement for the reaction of OClO with NO at 220-367 K
-
The reaction kinetics for the reaction OClO + NO → ClO + NO2 at 220-367 K was studied using fast flow coupled with MS. Under pseudo-first-order condition, the rate constant for the reaction of OClO with NO was in contrast to the positive temper
- Li,Wuebbles,Pylawka
-
p. 491 - 497
(2008/10/08)
-
- Quantum yield for ClOO formation following photolysis of aqueous OClO
-
The photochemistry of chlorine dioxide (OClO) in aqueous solution was investigated by femtosecond transient absorption spectroscopy. Following the photoexcitation of OClO at 400 nm, the transient absorption dynamics were probed in the spectral range from 400 to 220 nm. As expected from earlier studies, the main photolytic products ClO + O, formed with a quantum yield of ~90%, disappear through fast geminate recombination producing OClO in the electronic ground state. The total quantum yield for chlorine atom production is (ΦCl) ~10%, with the chlorine atom production occurring through two competing processes. The dominant channel for chlorine atom production involves the formation of a short-lived intermediate on a ~6 ps time scale with a quantum yield of 8 ± 2%. The remaining 2 ± 1% is formed through the formation and decomposition of ClOO. The lifetime of ClOO was found to be ~0.32 ns, in very good agreement with the result of a recent time-resolved resonance Raman study. Finally, the UV absorption spectrum for aqueous ClOO is reported and compared with previously reported spectra obtained in condensed media.
- Thomsen,Reid,Keiding
-
p. 12795 - 12801
(2007/10/03)
-
- Second Harmonic Generation Studies of Ozone Depletion Reactions on Ice Surfaces under Stratospheric Conditions
-
Hypochlorous acid, HOCl, an important species in the proposed heterogeneous mechanism for stratospheric ozone depletion, has been observed directly at submonolayer amounts on a single crystalline basal ice surface at 155-188 K, using the nonlinear optical method second harmonic generation. The ice is held in equilibrium with its vapor pressure. Second harmonic generation signals from 290 to 310 nm spectroscopically characterize the species and enable us to follow isothermal desorption kinetics in situ. HOCl desorbs as a single species with a ??G*des = 48 ?± 4 kJ/mol, close to the cohesive energy of ice itself. The lifetime of HOCl on the clean ice surface at 185 K is estimated to be 4 s and the equilibrium surface coverage at 10-11 Torr HOCl to be around 4 ?? 1011 molecules/cm2, corresponding to about 0.1% of a monolayer. However, these same measurements performed on ice predosed with varying amounts of HNO3 show that the HOCl lifetime is lengthened by coadsorbed HNO3, depending on the HNO3 surface density.
- Geiger, Franz M.,Tridico, Anthony C.,Hicks, Janice M.
-
p. 8205 - 8215
(2007/10/03)
-
- UV Photolysis of ClOOCl
-
ClOOCl (ClO dimer) photolysis is believed to dominate the catalytic destruction of polar stratospheric ozone during springtime through the production of atomic chlorine. Decomposition by an alternate pathway to form ClO would not catalyze ozone loss. Molecular beam experiments have demonstrated that photoexcitation of ClOOCl at both 248 and 308 nm leads to dissociation via multiple dynamical pathways, producing ClO + ClO and 2Cl + O2. At 248 nm, both concerted and sequential dissociation to 2Cl + O2 were observed. The primary dissociation channels occurred within a rotational period at both excitation wavelengths. The relative Cl:ClO product yields are 0.88:0.12 and 0.90:0.10 at 248 and 308 nm, respectively. Lower limits on these ratios were determined. These results substantially confirm the importance of ClOOCl photolysis in catalyzing springtime polar ozone depletion.
- Moore, Teresa A.,Okumura, Mitchio,Seale, James W.,Minton, Timothy K.
-
p. 1691 - 1695
(2007/10/03)
-
- Kinetics of the IO radical. 1. Reaction of IO with ClO
-
The rate coefficient for the IO + ClO → products (5) reaction was measured by coupling discharge flow and pulsed laser-induced fluorescence techniques. Rate coefficients were measured from 200 to 362 K by monitoring the temporal profile of IO in an excess of ClO. The rate coefficient is described by the expression: k5(T) = (5.1 ± 1.7) × 10-12 exp[(280 ± 80)/T] cm3 molecules-1 s-1 where the quoted uncertainties include estimated systematic errors. Atomic iodine was identified as a major product of reaction 5. A branching ratio of Φ = 0.14 ± 0.04 at 298 K was obtained for the sum of channels which do not produce I atoms.
- Turnipseed, Andrew A.,Gilles, Mary K.,Burkholder, James B.,Ravishankara
-
p. 5517 - 5525
(2007/10/03)
-
- Pressure dependence and metastable state formation in the photolysis of dichlorine monoxide (Cl2O)
-
The photolysis of dichlorine monoxide (Cl2O) is investigated using broadband photolysis source with time-resolved absorption spectroscopy. Time-dependent concentrations of reactants and products are measured by long-path uv absorption spectrosc
- Nickolaisen,Miller,Sander,Hand,Williams,Francisco
-
p. 2857 - 2868
(2008/10/09)
-
- A gaskinetic investigation of HOBr reactions with Cl(2P), O(3P) and OH(2Π). the reaction of BrCl with OH(2Π)
-
The reactions of HOBr with atomic chlorine (1), with oxygen (2) and with hydroxyl radicals (3) have been investigated at 300 K using the discharge flow technique with mass-spectrometric detection. The rate constants based on HOBr consumption have been determined to be k, = (8.0±0.4) · 10-11 and k2 = (3.1±0.2)· 10-11. For the reaction with OH radicals k3-13 was obtained. All rate constants are given in units cm3 molecule-1 s-1. The reactions of HOBr with Cl and with O are shown to proceed via bromine abstraction with formation of BrCl and BrO, respectively. The predominant channel in the reaction of OH with BrCl was identified to be step (4a) OH + BrCl → HOBr + Cl (4a) Based on the present kinetic investigation the heat of formation for HOBr at T = 300 K was evaluated to be ΔHf0 (HOBr) = -(60.22 ± 2) kJ · mol-1. VCH Verlagsgesellschaft mbH, 1996.
- Kukui,Kirchner,Benter, Th,Schindler
-
p. 455 - 461
(2007/10/03)
-
- Some Results on the Mechanism of the O (3P)-Atoms and HOCl. an Experimental and Ab Inition Model Study
-
The rate constant for the title reaction was redetermined using discharge flow technique and mass spectrometric measurements of HOC1 consumption. The overall rate constant k = (l.7±0.3)×10-13 cm3 molecule-1 s-1 was obtained and found to be practically independent of temperature in the range 213 K≤ T≤ 298 K. In experiments using 18O atoms the time dependence in the formation of the products 18O 16O, HCl and Cl2 was determined. Based on the experimental data available it is proposed that the reaction occurs via an intermediate complex mechanism but it could not be decided by which primary steps the reaction is initiated. Ab initio model calculations were carried out in an attempt 10 quantify conceived reaction pathways. Structures and energetics of the intermediates were computed. On the basis of these calculations it is suggested that Cl abstraction from HOC! should be regarded as the preferred initiation step. The O-atom attack leads to the formation of an intermediate HOClO. Alternative reaction pathways, like H abstraction from HOCl by O-atom attack, or a mechanism in which HO2 and Cl are formed were found to be less probable. In the present calculations no support could be found for the thermodynamically most preferred reaction route to contribute to product formation. Structure and energy of the intermediate HOClO are computed. VCH VerlagsgeseHschaft mbH, 1996.
- Schindler, Ralph N.,Dethlefs, Jan,Schmidt, Mark
-
p. 1242 - 1249
(2007/10/03)
-
- Primary and secondary dissociation pathways in the ultraviolet photolysis of Cl2O
-
The photodissociation of dichlorine monoxide (Cl2O) at 308, 248, and 193 nm was studied by photofragment translational energy spectroscopy.The primary channel upon excitation at 308 and 248 nm was Cl-O bond fission with production of ClO + Cl.A fraction of the ClO photoproducts also underwent spontaneous secondary dissociation at 248 nm.The center-of-mass translational energy distribution for the ClO + Cl channel at 248 nm appeared to be bimodal with a high energy component that was similar in shape to the 308 nm distribution and a second, low energy component with a maximum close to the threshold for the 2Cl + O(3P) channel.Observation of a bimodal distribution suggests that two pathways with different dissociation dynamics lead to ClO + Cl products.The high product internal energy of the second component raises the possibility that ClO is formed in a previously unobserved spin-excited state a 4Σ-.Following excitation at 193 nm, a concerted dissociation pathway leading to Cl2 + O was observed in addition to primary Cl-O bond breakage.In both processes, most of the diatomic photofragments were formed with sufficient internal energy that they spontaneously dissociated.The time-of-flight distributions of the Cl2 + O products suggest that these fragments are formed in two different channels Cl2(3Π) + O(3P) and Cl2(X 1Σ) + O(1D).
- Nelson, Christine M.,Moore, Teresa A.,Okumura, Mitchio,Minton, Timothy K.
-
p. 8055 - 8064
(2007/10/02)
-
- Eine gaskinetische Studie zur Reaktion von HOCl mit F-, Cl- und H-Atomen bei Raumtemperatur
-
Chemical Kinetics / Elementary Reactions / Fluorescence / Mass Spectrometry / Radicals.The reactions of HOCl with F-, Cl- and H-atoms were investigated at room temperature in a discharge flow system equipped with an OH-resonance fluorescence cell and a mass spectrometric detector.All kinetic studies were carried out under pseudo first order conditions with HOCl being the minority component.Branching ratios for individual processes were obtained by following simultaneously the rates of HOCl consumption and product formation.The following rate constants (in units cm3 molecule-1 s-1) were determined: .Calibration for using reaction (1) for gas titration is discussed.The data are evaluated to yield ΔHf = -79.7 kJ mol-1 for the heat of HOCl formation.
- Vogt, R.,Schindler, R.N.
-
p. 819 - 829
(2007/10/02)
-
- Dynamics of the O(1D) + ClNCO Reaction
-
The reaction of excited O(1D) atoms with ClNCO was studied by pulsed photolysis of O3/ClNCO mixtures with the 249-nm output of a KrF laser.The rate constant for O(1D) quenching by ClNCO was determined to be k = (1.3 -+/- 0.3) * 10-10 cm3 s-1.Investigation of the possible products of this reaction indicated that production of ClO + NCO is a major channel, with a branching fraction greater than 0.20.No evidence was found for the production of NCl in its X3Σ-, a1Δ, or b1Σ+ states.An upper limit for the branching fraction to NCl + CO2 is 0.005.
- Singleton, Steven M.,Coombe, Robert D.
-
p. 9865 - 9870
(2007/10/02)
-
- Non-metal redox kinetics: Reactions of trichloramine with ammonia and with dichloramine
-
Trichloramine reacts with excess NH3 and base (B) with the rate expression -d[NCl3]/dt = 2kB[B][NH3][NCl3], based on the overall stoichiometry 2NCl3 + 3NH3 + 3OH- → 3NH2Cl + N2 + 3Cl- + 3H2O. The reaction is general-base assisted with kB values (M-2 s-1, 25.0°C, μ = 0.50 M) of 4.46 × 103 for OH-, 3.3 × 103 for PO43-, and 22 for NH3. A water path with kH2O = 2.2 M-1 s-1 and an acidic phosphate path for H2PO4- (kHB = 450 M-2 s-1) are also found. The rate-determining step in the proposed mechanism is a Cl+ transfer between NCl3 and NH3 to give HNCl2 and NH2Cl. This is followed by N2 formation in a rapid base-assisted reaction between NCl3 and HNCl2 with the rate expression -d[NCl3]/dt = kB′[B][HNCl2][NCl3], based on the stoichiometry NCl3 + HNCl2 + 3OH- → N2 + 2HOCl + 3Cl- + H2O. Values of kB′ (M-2 s-1, 25.0°C, μ = 0.50 M) are 2.92 × 104 for HPO42- and greater than 4 × 107 for OH-. The HOCl released in the formation of N2 reacts with excess NH3 to give more NH2Cl, which accounts for the overall stoichiometry of 1.5 NH2Cl formed per NCl3. The reaction between NCl3 and HNCl2 is of critical importance in the explanation of breakpoint chlorination processes.
- Yiin, Boudin S.,Margerum, Dale W.
-
p. 2135 - 2141
(2008/10/08)
-
- Studies with ClONO2: Thermal Dissociation Rate and Catalytic Conversion to NO Using an NO/O3 Chmiluminescence Detector
-
A NO/O3 chemiluminescence detector equipped with a gold catalyst is adapted to provide a measure of the thermal decomposition rate of ClONO2 in an N2/O2 gas mixture and, in a related way, provide the absolute concentration of ClONO2 in a flowing gas stream.The apptoach is to add ClONO2, in the parts per million by volume (ppmv) range, to the flow stream of the detector in the presence of excess NO.As the sample is heated, ClONO2 is thermally dissociated and the subsequent scavenging reaction of ClO with NO produces Cl and NO2.Cl goes on to react with ClONO2 to form NO3 which, in turn, reacts with NO to produce NO2.The loss of NO from the flow is precisely monitored downstream in the detector by the change in the chemiluminescence produced in the reaction of NO with reagent O3.If the reaction rates with NO are given, the NO loss at fixed temperature can be modeled to yield a dissociation rate constant for ClONO2.Results were obtained for temperatures between 353 and 413 K and for pressures in the range of 66-160 Torr (8.8-21.3 kPa).The data is best fit by the expression 1E-6.16exp(-90.7 kJmol-1/RT)cm3s-1molecule-1, which is in good agreement with earlier results.When combined with the rate constant for the association reaction of ClO and NO2, these results yield a larger equilibrium constant for the reactiothan indicated in previous direct measurements.A value for Δaf289.15 for ClONO2 of 22.9 kJmol-1 is obtained from a third-law thermochemical analysis of the data.The initial ClONO2 concentration in the sample is assumed to equal the absolute loss of NO measured when the dissociation and scavenging reactions have gone to completion.This affords the opportunity to calibrate the efficienty of other methods for the detection of ClONO2.Results are presented for the conversion efficienty of ClONO2 to NO found for a gold catalyst at 573 K with CO present as a reducing agent.
- Anderson, L. C.,Fahey, D. W.
-
p. 644 - 652
(2007/10/02)
-
- Kinetics and Mechanism of X + ClNO -> XCl + NO (X = Cl, F, Br, OH, O, N) from 220 to 450 K. Correlation of Reactivity and Activation Energy with Electron Affinity of X
-
The rate constants for a series of radical reactions with ClNO, X + ClNO -> products where X = Cl, F, Br, OH, O, N, have been measured as a function of temperature in discharge flow systems at pressures between 1 and 2 Torr of helium buffer gas.Radicals were detected by resonance fluorescence (X = Cl, Br, OH, O), laser magnetic resonance (X = OH), and chemical conversion/resonance fluorescence (X = F, N).The rate constants, with units of cm3 molecule-1 s-1 and to 95 percent confidence level, are for Cl + ClNO -> Cl2 + NO, e(-128+/-46)/T; for F + ClNO -> FCl + NO, e(-28+/-84)/T; for Br + ClNO -> BrCl + NO, e(-52+/-43)/T; for OH + ClNO -> ClOH + NO, e(-1130+/-170)/T; for OH + ClNO -> HONO + Cl, e(240+/-130)/T; for O + ClNO -> ClO + NO, e(-1520+/-36)/T; and for N + ClNO -> NCl + NO, e(-2250+/-90)/T.Both the reaction activation energies and the logarithms of the room temperature rate constants are found to correlate strongly with the affinity of the radical in such a way that high electron affinity leads to enhanced reactivity.The reactivity trend is rationalized by a frontier orbital interaction dominated by the ease with which electron transfer from the CINO molecule to the X radical can occur to stabilize a polar transition state, a mechanism shown to be widely prevalent in radical-molecule systems.The propensity for this type of interaction is determined by the energy required for electron transfer which, in this case, is given by IPCINO - EAX, where IP refers to ionization potemtial and EA to electron affinity.In addition, the A factors for the X/CINO reactions are found to increase as the electron affinity of the radical increases, indicating that the tightness of the reansition state is directly related to the height of the activation barrier.
- Abbatt, J. P. D.,Toohey, D. W.,Fenter, F. F.,Stevens, P. S.,Brune, Wm. H.,Anderson, J. G.
-
p. 1022 - 1029
(2007/10/02)
-
- Study of the Reaction ClO + CH3O2 --> Products at 300 K
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The first experimental study of the reaction ClO + CH3O2 --> products (1) is reported.The rate coefficient k1 and the product distribution were investigated in the modulated photolysis of Cl2/CH4/Cl2O/O2 mixtures.Reactants and products have been monitored by using UV-vis and Fourier-transform infrared gas-phase absorption spectroscopies.The value of k1 was found to be equal to (3.1 +/- 1.7)E-12 cm3 molecule-1 s-1 at 300 K and 240 Torr total pressure.The product channnel forming ClOO and CH3O appears to be dominant pathway at 300 K.The subsequent oxidation of CH3O to CH2O and its partial photolysis into H and HCO leads to enhanced production of odd hydrogen (OH, HO2) radicals.Consequently, high concentrations of OH radicals can built up, leading to an additional source of active chlorine via the reaction HCl + OH --> Cl + H2O, which destroys ozone by catalytic reactions.This strongly suggests that reaction 1 can play a substantial role in the photochemical processes that take place under stratospheric "ozone hole" conditions.
- Simon, F. G.,Burrows, J. P.,Schneider, W.,Moortgat, G. K.,Crutzen, P. J.
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p. 7807 - 7813
(2007/10/02)
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