- Collision energy dependence of the O(1D) + HCl -OH + Cl( 2P) reaction studied by crossed beam scattering and quasiclassical trajectory calculations on ab initio potential energy surfaces
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The dynamics of the O(1D) + HCl → OH + Cl(2P) reaction are investigated by a crossed molecular beam ion-imaging method and quasiclassical trajectory calculations on the three ab initio potential energy surfaces, the ground 11A′ and two excited (1 1A″ and 21A′) states. The scattering experiment was carried out at collision energies of 4.2, 4.5, and 6.4 kcal/mol. The observed doubly differential cross sections (DCSs) for the Cl(2P) product exhibit almost no collision energy dependence over this inspected energy range. The nearly forward-backward symmetric DCS indicates that the reaction proceeds predominantly on the ground-state potential energy surface at these energies. Variation of the forward-backward asymmetry with collision energy is interpreted using an osculating complex model. Although the potential energy surfaces obtained by CASSCF-MRCI ab initio calculations exhibit relatively low potential barriers of 1.6 and 6.5 kcal/mol for 1 1A″ and 21A′, respectively, the dynamics calculations indicate that contributions of these excited states are small at the collision energies lower than 15.0 kcal/mol. Theoretical DCSs calculated for the ground-state reaction pathway agree well with the observed ones. These experimental and theoretical results suggest that the titled reaction at collision energies less than 6.5 kcal/mol is predominantly via the ground electronic state.
- Kohguchi, Hiroshi,Suzuki, Toshinori,Nanbu, Shinkoh,Ishida, Toshimasa,Mil'nikov, Gennady V.,Oloyede, Ponmile,Nakamura, Hiroki
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- Photodissociation dynamics of phosgene: New observations by applying a three-dimensional imaging technique
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The three-dimensional (3D) momentum vector of single Cl atoms in the uv photodissociation of phosgene was directly observed using the recently developed 3D imaging technique. The previous results as there is the generation of chlorine in the 2P/3/2 electronic ground state as well as in the electronically excited 2P1/2 state, the highly spin selective process with bimodal kinetic energy distribution and the overall decay mechanism as well as the branching ratios were confirmed. The anisotropy parameter β and its speed dependence were observed for the first time.
- Einfeld, Tina,Chichinin, Alexei,Maul, Christof,Gericke, Karl-Heinz
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- Nonradiative decay pathways of electronic states of group IV tetrafluoro and tetrachloro molecular ions studied with synchrotron radiation
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The nonradiative decay channels of the valence electronic states of the gas-phase tetrahedral ions CF4+, SiF4+, CCl4+, SiCl4+, and GeCl4+ have been studied in the range 35-100 nm by a novel form of photoionization mass spectrometry.Tunable vacuum UV radiation from a synchrotron source ionizes the parent neutral molecule, and electrons and ions are detected by the photoelectron-photoion coincidence technique.The experiment is repeated continuously as a function of photon energy, and a three-dimensional histogram of photon energy versus ion time of flight versus coincidence count rate is produced.By taking cuts through this histogram, photoionization curves for the different fragment ions can be extracted.The appearance energies of the fragment ions (e.g., CF2+ from CF4, CCl+ from CCl4) occur at the adiabatic ionization potential of an electronic state of the parent ion, and not at the thermodynamic appearance energy of that ion.Attempts to measure the kinetic-energy releases in the fragmentation pathways have only been partially successful.The results are complementary to those of recent experiments to probe the radiative decay of these electronic states of MX4+ , where the T2 and A1 third and fourth excited electronic states can show radiative decay to a surprising degree.The decay dynamics of the and states of MX4+ are reviewed.In general, the fluorides show different behavior to the analogous chlorides, and the carbon species behaves differently to the corresponding silicon or germanium species.
- Creasey, J. C.,Lambert, I. R.,Tuckett, R. P.,Codling, K,Frasinski, L. J.,at al.
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- Primary and secondary dissociation pathways in the ultraviolet photolysis of Cl2O
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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.
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- Thermochemistry is not a lower bound to the activation energy of endothermic reactions: A kinetic study of the gas-phase reaction of atomi-chlorine with ammonia
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The rate constant for Cl + NH3 → HCl + NH2 has been measured over 290-570 K by the time-resolved resonance fluorescence technique. Ground-state Cl atoms were generated by 193 nm excimer laser photolysis of CCl4 and reacted under pseudo-first-order conditions with excess NH3. The forward rate constant was fit by the expression k1 = (1.08 ± 0.05) × 10-11 exp(-11.47 ± 0.16 kJ mol-1/RT) cm3 molecule-1 s-1, where the uncertainties in the Arrhenius parameters are ±1 σ and the 95% confidence limits for k1 are ±11%. To rationalize the activation energy, which is 7.4 kJ mol -1 below the endothermicity in the middle of the 1/T range, the potential energy surface was characterized with MPWB1K/6-31++G(2df,2p) theory. The products NH2 + HC1 form a hydrogen-bonded adduct, separated from Cl + NH3 by a transition state lower in energy than the products. The rate constant for the reverse process k-1 was derived via modified transition state theory, and the computed k-1 exhibits a negative activation energy, which in combination with the experimental equilibrium constant yields k1 in fair accord with experiment.
- Gao, Yide,Alecu,Hsieh,Morgan, Brad P.,Marshall, Paul,Krasnoperov, Lev N.
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- Measuring gas-phase chlorine atom concentrations: Rate constants for Cl + HN3, CF3I, and C2F5I
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A convenient method is reported for the measurement of gas-phase Cl atom concentrations in the 1011-1013 atoms cm-3 range in a flow reactor. The titration reaction with vinyl bromide is used to measure the absolute Cl atom concentration, and the relative Cl atom concentration is monitored by the HCl(ν) infrared emission intensity produced by the reaction of Cl atoms with hydrogen sulfide. A microwave discharge through dilute flows of Cl2, CCl4, CFCl3, and CF2Cl2 in Ar were characterized as sources of Cl atoms in the flow reactor. The elementary rate constants for reaction of Cl atoms with HN3, CF3I, and C2F5I were measured as (1.1 ± 0.3) × 10-12, (5.1 ± 1.5) × 10-13, and (3.9 ± 0.8) × 10-12 cm3 molecule-1 s-1, respectively, at 300 K. These rate constants were obtained after adjustment of the apparent rate constants for secondary reactions.
- Manke II,Setser
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- Surface aligned photochemistry: photodissociation of Cl2 and Cl2...Cl adsorbed on LiF (001)
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In this study, an attempt was made to photolyze chlorine from submonolayer to multilayer coverage on a nonreactive dielectric substrate, LiF(001). Low laser energies and chlorine coverages were used in order to observe photochemical processes. An additional channel referred to as channel A for Cl atoms was found for photodissociation of chlorine adsorbed on LiF(001) surface by 351 nm laser radiation.
- Giorgi, Javier B.,Naumkin, Fedor Y.,Polanyi, John C.,Raspopov, Sergei A.,Sze, Newman S. -K
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- A laser flash photolysis-resonance fluorescence kinetics study of the reaction Cl(2P) + CH4 -> CH3 + HCl
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The technique of laser flash photolysis-resonance fluorescence is employed to study the kinetics of the reaction Cl(2P) + CH4 -> CH3 + HCl over the temperature range 221-375 K.Chlorine atoms are produced by photolysis of Cl2 at 355 nm.At temperatures =1L) and high (klH) methane concentrations.For Cl2/CH4/CCl4/He and Cl2/CH4/Ar reaction mixtures, the bimolecular rate constant (k1) is independet of methane concentration with k1 ca. k1L. k1 and k1L are in good agreement with previous results obtained using the flash photolysis-resonance fluorescence technique while k1H is in good agreement with previous results obtained using the didcharge flow-resonance fluorescence and competitive chlorination techniques.At 298 K the measured bimolecular rate constant is independet of the identity of the chemically inert gases in the reaction mixture and in good agreement with all previous investigations.The low temperature results obtained in this investigation and all previous investigations can be rationalized in terms of a model which assumes that the Cl(2P1/2) state reacts with CH4 much faster than the Cl(2P3/2) state.Extrapolation of this model to higher temperatures, however, is not straightforward.
- Ravishankara, A. R.,Wine, P. H.
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- Mechanism and Rate Constants for the Reactions of Cl Atoms with HOCl, CH3OCl and tert-C4H9OCl
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Reactions of Cl atoms with HOCl (1), CH3OCl (2) and C4H9OCl (3) have been investigated at 300 K using discharge flow LIF/MS technique. The mechanism and reaction rate constants were determined by monitoring absolute rates of hypochlorite and Cl atom consumption together with the build-up of reaction products. Based on the yields of Cl2 and OH in (1a), Cl2 and CH3O in (2a) and Cl2 in (3a), as measured by MS/LIF, the reactions of Cl atom with the hypochlorites investigated in this work were found to proceed predominantly via the Cl atom abstraction channel with k1a/k1 = (0.96±0.05), k2a/k2 = (0.85±0.06), k3a/k3 = (1.01 ±0.05). HOCl + Cl → Cl2 + OH (1a) CH3OCl+Cl → Cl2 + CH3O (2a) C4H9OCl + Cl→ Cl2 +other products (3a) The reaction rate constants were determined to be k1, = (2.28±0.09)·10-12, k2 = (6.0±0.2)·10-11, and k3 = (4.26±0.2)·10-11, all in units cm3-molecule-1·s-1. A reevaluation of the heat of formation of HOCl yielded ΔHf0 (298 K) = -75.1 kJ·mol-1. VCH Verlagsgesellschaft mbH 1997.
- Kukui,Roggenbuck,Schindler
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- The rate and equilibrium constants for the reaction NO3? + Cl- ? NO3- + Cl? in aqueous solutions
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The rate and equilibrium constants for the reaction NO3? + Cl- ? NO3- + Cl? in aqueous solutions were measured by pulse radiolysis. The formation and decay of the nitrate radical, NO3?, and the dichloride radical anion, Cl2?-, in irradiated aqueous solutions containing nitric acid and chloride ions were followed under various conditions. Because of the complexity of the system, the forward rate constant and the equilibrium constant were derived from modeling the experimental results, including secondary formation and decay reactions. The modeling study results in an equilibrium constant of Keq = (3.5 ± 0.5) at an ionic strength between 0.1 and 1 mol L-1 and a forward rate constant k1 = (3.5 ± 0.5) × 108 L mol-1 s-1. In contrast with previous reports, no effect of ionic strength (up to 2 mol L-1) on the forward rate constant was observed.
- Poskrebyshev,Huie,Neta
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- The photodissociation of ClNO2 in argon and water clusters studied at 235 nm by the REMPI-TOF method
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The photodissociation of ClNO2 embedded in argon and water clusters was investigated at 235 nm by detecting the Cl(2P3/2) photofragments with resonance enhanced multiphoton ionization time-of-flight spectroscopy (REMPI-TOF). Under various cluster formation conditions the speed distributions of Cl(2P3/2) were recorded. In contrast to the monomer photolysis only one decay channel was found to be active showing the fragments to be Boltzmann distributed and isotropic. In view of atmospheric chemistry, CINO2 in water clusters is a photolytical source of Cl and NO2 radicals with low translational and internal energy. They are thus less favorable for consecutive reactions than the monomer products.
- Li, Qiang,Robert Huber
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- Rate coefficient temperature dependence and branching ratio for the OH + CIO reaction
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OH + ClO-->HO2 + Cl (1a) -->HCl + O2 (1b) has been measured in a discharge-flow system with far infrared laser magnetic resonance detection of OH, C1O, and HO2.Measurements were made at low pressure ( 1.0-1.1 Torr) and at temperatures between 219 and 373 K under pseudo-first-order conditions.The measured rate constant is k1 = (8.0+/-1.4)*10-12exp cm3 molecule-1 s-1.The branching ratio at 293 K is, k1a/k1 = 0.86+/-0.14.The rate constant to channel (1a) was used with that for the reverse reaction to calculate the heat of formation of HO2.ΔH0f,298(HO2) = 3.0+/-0.4 kcal mol-1.
- Hills, Alan J.,Howard, Carleton J.
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- ESR of matrix isolated bromine atoms produced in the H + Br2 reaction
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The products of the H(D) + X2 reaction, where X is Br, Cl, or F, have been trapped in solid argon at 4 K and observed via ESR.With Br2 as reactant the observed spectra are attributed to Br atoms electronically quenched in an axial crystal field.The spectra obtained using the other halogens were not clearly attributable to quenched atoms.The ESR of matrix-isolated Br atoms has not been observed previousls, > but their magnetic properties are similar to those recently observed by Iwasaki, Toriyama, and Muto for I atoms queched in solid xenon.For Br: g = 2.646(1),g = 1.55(1),/A/ = 1937(20)MHz, /A/ = 423(10) MHz, and Q = 100(10) MHz.Comparison was made with crude axial crystal field predictions derived using the magnetic parameters of the gas-phase atoms.
- Bhat, S. V.,Weltner, W.
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- Dynamics of the H+HCl gas-phase reaction: Absolute reactive cross-section for Cl(2P3/2) atom formation
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The reaction of atomic hydrogen with HCl was studied in the gas phase using the laser photolysis/vacuum-UV laser-induced fluorescence (LP/VUV-LIF) 'pump-and-probe' technique. Translationally energetic H atoms with an average energy of Ecm=1.0 eV in the (H-HCl)-center-of-mass system were generated by laser photolysis of H2S at 248 nm. Doppler profiles of nascent Cl(2P3/2) atoms produced in the reactive collision of the H atoms with room temperature HCl molecules were measured under single collision conditions by VUV-LIF. For the H+HCl→H2+Cl(2P3/2) reaction an absolute reaction cross-section σR(1.0 eV)=(0.34±0.05) A2 was determined by means of a photolytic calibration method using the 248 nm laser photolysis of PCl3 as reference for well-defined concentrations of Cl atoms. Small amounts of Cl in the (2P1/2) excited state were observed in the H+HCl experiments. An upper limit of (0.02±0.01) A2 was measured for the Cl*(2P1/2) formation cross-section in the H+HCl reaction at 1.0 eV.
- Brownsword,Kappel,Schmiechen,Upadhyaya,Volpp
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- The effect of reagent translational excitation on the dynamics of the reaction H+Cl2 -> HCl(v',J')+Cl
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We use fast time-resolved Fourier transform spectroscopy and low pressure infrared chemiluminescence techniques to determine the product energy distribution in the title reaction.We create the reagent hydrogen atoms with 2.3 eV of translational excitation
- Berg, P. A.,Sloan, J. J.
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- ON THE DECAY OF THE DICHLORIDE ANION Cl2 - IN AQUEOUS SOLUTION.
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The decay kinetics of Cl//2** minus , produced by photolysis of chloride ions, has been studied using a flash photolysis technique with conductometric detection. Flash photolysis of Cl** minus ions in acid solutions eventually yields H//2O//2, Cl//2, HClO and H//2. A mechanism is proposed (Fig. 6) consistent with the experimental observations.
- Wagner,Karthaeuser,Strehlow
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- Infrared frequency-modulation measurements of absolute rate coefficients for Cl+HD→HCl(DCl)+D(H) between 295 and 700 K
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Absolute rate coefficients and HCl branching fractions for the Cl+HD reaction have been measured. The rate coefficient for Cl+HD is fit well by k1=(1.28±0.18)×10-16 T1.67 e-(1646±60)/T cm3 moleculesu
- Taatjes, Craig A.
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- Competing dissociation channels in the photolysis of S2Cl2 at 235 nm
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The photodissociation of disulfur dichloride at 235 nm was investigated by three-dimensional (3D) imaging of the chlorine product recoil in its ground state and excited spin-orbit state. The resonance increasing muliphoton ionization and time-of-flight techniques were used. The dependence of anisotropy parameter on the fragment recoil velocity was determined due to the technique where the 3D momentum vector of a single reaction product was found.
- Einfeld, Tina S.,Maul, Christof,Gericke, Karl-Heinz,Chichinin, Alexei
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- Pulsed laser photolysis kinetics study of the O(3P)+ClO reaction
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A pulsed laser photolysis technique has been employed to study the kinetics of the important stratospheric reaction O + ClO Cl + O2 in N2 buffer gas over the temperature and pressure ranges 231-367 K and 25-500 Torr. 351 nm pulsed laser photolysis of Cl2/O3/N2 mixtures produced Cl atoms in excess over O3.After a delay sufficient for the reaction Cl + O3-->ClO + O2 to go to completion, a small fraction of the ClO was photolyzed at 266 nm to produce O(3P).The decay of O(3P) in the presence of an excess, known concentration of ClO was then followed by time-resolved resonance fluorescence spectroscopy.We find that k1 is independent of pressure, but that k1( T) increases with decreasing temperature.Our results suggest that the Arrhenius expression k1( T) = ( 1.55 +/- 0.33 )*10-11exp cm3 molecule-1 s-1 is appropriate for modeling stratospheric chemistry.Errors in the Arrhenius expression are 2δ and represent precison only.The absolute accuracy of k, at any temperature within the range studied is estimated to be + 20percent.Our results agree with other recent measurements of k1 at 298 K but give significantly faster rate coefflcients at stratospheric temperatures.A few measurements of the rate coefflcient for the reaction ClO + ClO products were also carried out.These measurements were necessary to assess the time dependence of .
- Nicovich, J. M.,Wine, P. H.,Ravishankara, A. R.
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- Spin-orbit branching ratios for the Cl atom photofragments following the excitation of Cl2 from 310 to 470 nm
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Velocity distributions for the Cl(2P3/2) and Cl(2P1/2) photofragments produced by photolysis of Cl2 in the region between 310 and 470 nm are measured using photofragment velocity mapping. Our results indicate that at short wavelengths the absorption spectrum is dominated by the 1u(1Πu) excited electronic state which produces two ground state chlorine atoms. The 0+u(B 3Πu) state which produces a spin-orbit excited and a ground state chlorine atom becomes significant at 350 nm and dominates the spectrum beyond 400 nm. Analysis of the photofragment angular distributions indicates that the Cl(2P3/2) photofragments are aligned and the magnitude of the alignment is quantitatively determined. Nonadiabatic curve crossing between the 1u(1Πu) and the 0+u(B 3Πu) electronic states is observed and quantified below 370 nm. The measured nonadiabatic transition probability is modeled using the Landau-Zener formula and the position of the curve crossing is estimated at ~3 eV above the zero-point of ground electronic state of Cl2.
- Samartzis, Peter C.,Bakker, Bernard L. G.,Rakitzis, T. Peter,Parker, David H.,Kitsopoulos, Theofanis N.
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- High-Temperature Fast-Flow Reactor Kinetics Studies of the Reactions of Al with Cl2, Al with HCl, and Wide Temperature Ranges
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The high-temperature fast-flow reactor (HTFFR) technique has been used to measure rate coefficients for the title reactions under pseudo-first-order conditions.The relative concentrations of the minor reactants (Al species) were monitored by laser-induced fluorescence.The following k(T) expressions in cm3 molecule-1 s-1 are obtained: Al + Cl2 -> AlCl + Cl, k1(T) = 7.9 x 1E-10 exp(-780K/T) between 425 and 875 K; Al + HCl -> AlCl + H, k2(T) = 1.5 x 1E-10 exp(-800K/T) between 475 and 1275 K; AlCl + Cl2 -> AlCl2 + Cl, k3(T) = 9.6 x 1E-11 exp(-610K/T) between 400 and 1025 K.Confidence limits are given in the text.Indications are obtained that the expressions for k1(T) and k2(T) are approximately valid to at least 1300 and 1700 K, respectively.The reasults are discussed in terms of a harpooning mechanism and a modified form of collision theory, which takes account of long-range attractive potentials and conservation of angular momentum.
- Rogowski, Donald F.,Marshall, Paul,Fontijn, Arthur
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- Kinetics, mechanism, and thermochemistry of the gas phase reaction of atomic chlorine with dimethyl sulfoxide
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A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of the reaction of chlorine atoms with dimethyl sulfoxide (CH3S(O)CH3; DMSO) as a function of temperature (270-571 K) and pressure (5-500 Torr) in nitrogen bath gas. At T = 296 K and P ≥ 5 Torr, measured rate coefficients increase with increasing pressure. Combining our data with literature values for low-pressure rate coefficients (0.5-3 Torr He) leads to a rate coefficient for the pressure independent H-transfer channel of k1a = 1.45 × 10-11 cm3 molecule -1 s-1 and the following falloff parameters for the pressure-dependent addition channel in N2 bath gas: k1b,0 = 2.53 × 10-28 cm6 molecule-2 s -1; k1b,∞ = 1.17 × 10-10 cm 3 molecule-1 s-1, Fc = 0.503. At the 95% confidence level, both k1a and k1b(P) have estimated accuracies of ±30%. At T > 430 K, where adduct decomposition is fast enough that only the H-transfer pathway is important, measured rate coefficients are independent of pressure (30-100 Torr N2) and increase with increasing temperature. The following Arrhenius expression adequately describes the temperature dependence of the rate coefficients measured at over the range 438-571 K: k1a, = (4.6 ±0.4) × 10-11 exp[-(472 ± 40)/T) cm3 molecule-1 s-1 (uncertainties are 2σ, precision only). When our data at T > 430 K are combined with values for k1a at temperatures of 273-335 K that are obtained by correcting reported low-pressure rate coefficients from discharge flow studies to remove the contribution from the pressure-dependent channel, the following modified Arrhenius expression best describes the derived temperature dependence: k1a = 1.34 × 10-15T1.40 exp(+383/T) cm3 molecule-1 s-1 (273 K ≤ T ≤ 571 K). At temperatures around 330 K, reversible addition is observed, thus allowing equilibrium constants for Cl-DMSO formation and dissociation to be determined. A third-law analysis of the equilibrium data using structural information obtained from electronic structure calculations leads to the following thermochemical parameters for the association reaction: ΔrH298o = -72.8 ±2.9 kJ mol -1, ΔHo0 = -71.5 ±3.3 kJ mol -1, and ΔrS298o = -110.6 ±4.0 J K-1 mol-1. In conjunction with standard enthalpies of formation of Cl and DMSO taken from the literature, the above values for Δrffo lead to the following values for the standard enthalpy of formation of Cl-DMSO: ΔfH298 o = -102.7 ± 4.9 kJ mol-1 and Δ rHo0 = -84.4 ±5.8 kJ mol-1. Uncertainties in the above thermochemical parameters represent estimated accuracy at the 95% confidence level. In agreement with one published theoretical study, electronic structure calculations using density functional theory and G3B3 theory reproduce the experimental adduct bond strength quite well.
- Nicovich,Parthasarathy,Pope,Pegus,McKee,Wine
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- Diode laser probes of vinyl radical kinetics: The reaction of C2H3 with HCl and DCl
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A tunable diode laser probe is used to measure the rate of reaction of vinyl radicals with HCl and DCl at room temperature.Rate constants for reaction with HCl and DCl are (1.3 +/- 0.3) * 10-12 and (7.8 +/-1.6) * 10-13 cc/molecule s, respectively.These rate constants are about five orders of magnitude faster than the estimated rate constant for reaction of vinyl radicals with H2, and potential reasons for these differences are considered within the context of the BSBL (bond strength-bond length) model of atom abstraction reactions.The rate constant for reaction of C2H3 with O2 is determined to be (1.0 +/- 0.4) * 10-11 cc/molecule s, in excellent agreement with a previous determination.Finally, the temperature dependence of the vinyl radical + HCl rate constant is reported.The rate constant is found to decrease by approximately 33percent over the temperature range of 278-370 K.This change, however, is within the experimental error of the measured rate constants.From these measurements, an activation energy of - 840 +/- 1400 (2?) cal/mol is obtained.
- Krueger, Herman,Weitz, Eric
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- Photodissociation of Phosgene on Pd(111) at 193 nm
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The UV photodissociation of phosgene (Cl2CO) on Pd(111) has been studied by isothermal mass spectrometry during irradiation and by temperature-programmed desorption and X-ray photoelectron spectroscopy following irradiation.Phosgene, which adsorbs reversibly on Pd(111) at 110 K, undergoes photodissociation when irradiated with 6.4-eV photons, resulting in the evolution of CO and retention of chlorine adatoms.Photolysis rates have been monitored as a function of photon flux and, using polarized light, as a function of incident angle.The initial photodissociation crosssection is (5.3 +/- 0.8) x 10-18 cm2, higher than the gas-phase absorption cross section.The angular response of the photolysis yield is interpreted using a mechanism driven by photoexcited substrate electrons.
- Flores, C. R.,Zhu, X.-Y.,White, J. M.
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- Kinetics of the reactions of chlorine atoms with a series of acetates
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The kinetics of the reactions of Cl atoms with a series of alkyl acetates were investigated using relative and absolute rate methods in 2-700 Torr of N2 at room temperature. Consistent results were obtained using the two methods. The data from
- Xing, Jia-Hua,Takahashi, Kenshi,Hurley, Michael D.,Wallington, Timothy J.
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- Chlorine atom spin-orbit branching ratios and total absolute reaction cross-sections for the H+DCl→HD+Cl reaction
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Chlorine atom spin-orbit product branching ratios and total absolute reaction cross-sections have been measured for the H+DCl→HD+Cl gas-phase reaction for collision energies of Ecol=1.0,1.4 and 1.7 eV. The measured Cl*(2P1/2) atom spin-orbit product branching ratios φCl*(1.0eV)=[Cl*]/[Cl+Cl*]=(0.06±0.02), φCl*(1.4eV)=(0.07±0.01), and φCl*(1.7eV)=(0.16±0.01) revealed the increasing importance of a non-adiabatic reaction channel H+DCl→HD+Cl* with increasing collision energy. The measured total absolute reaction cross-sections allow for comparison with results from recent quasi-classical trajectory (QCT) calculations [F.J. Aoiz et al. J. Phys. Chem. A 104 (2000) 10452].
- Hanf, Alexander,L?uter, Almuth,Suresh, Dhanya,Volpp, Hans-Robert,Wolfrum, Jürgen
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- UV Photolysis of ClOOCl
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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.
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- Reactions of Hyperthermal C(3P) Generated by Laser Ablation with H2, HCl, HBr, and CH3OH
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The reactions of C(3P) with H2, HCl, HBr, and CH3OH(D) were investigated in a crossed-beam configuration using laser ablation of graphite as the source of C(3P).Upon pulsed irradiation of graphite with focused laser output at 266 and 355 nm, hyperthermal C(3P) is produced and expands freely into the vacuum.In this free ablation mode, directional beams of monomeric carbon are produced with a peak velocity of ca. 8000 m s-1 and a broad velocity distribution that can be described by temperatures of ca. 21000 and ca. 9500 K when using 266 and 355 nm ablation wavelengths, respectively.Using 266 nm ablation, the endothermic reactions of C(3P) with the title molecules were investigated by probing the CH product.CH is produced predominantly in ν = 0 with rotational distributions that are well described by temperatures in the range 1500-2200 K, depending on the molecular reactants.The spin-orbit and Λ-doublet sublevels are equally populated.In reactions with CH3OD, both CH and CD are detected, identifying both the methyl and the hydroxyl groups as reactive sites.Comparisons with the CH internal energy distributions obtained in the reaction of C(1D) with H2 show remarkable similarities.On the basis of theoretical investigations and the known electronic states of the methylene intermediate, it is suggested that the reactions of both C(3P) and C(1D) proceed via insertion involving carbene intermediates.The participation of several low-lying states of the carbenes may lead both to lowering of the activation barrier for insertion and to CH products with similar populations of the two Λ-doublet components.
- Scholefield, M. R.,Goyal, S.,Choi, J.-H.,Reisler, H.
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- Kinetics of the Reaction of Cl with ClNO and ClNO2 and the Photochemistry of ClNO2
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The room temperature rate constants for the reactions Cl+ClNO (2) and Cl+ClNO2 (4) have been measured by the method of laser flash photolysis/resonance fluorescence.The rate constants obtained are (k2+/-2?)=(1.65+/-0.32)E-11 cm3ssup
- Nelson, H. H.,Johnston, H. S.
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- Experimental and theoretical study of the carbon-13 and deuterium kinetic isotope effects in the Cl and OH reactions of CH3F
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A laser flash photolysis-resonance fluorescence technique has been employed to determine absolute rate coefficients for the CH3F + Cl reaction in N2 bath gas in the temperature range of 200-700 K and pressure range of 33-133 hPa. The data were fitted to a modified Arrhenius expression k(T) = 1.14 × 10-12 x (T/ 298)226 exp{-313/T}. The OH and Cl reaction rates of 13CH3F and CD3F have been measured by long-path FTIR spectroscopy relative to CH3F at 298 ± 2 K and 1013 ± 10 hPa in purified air. The FTIR spectra were fitted using a nonlinear least-squares spectral fitting method including line data from the HITRAN database and measured infrared spectra as references. The relative reaction rates defined by α = klight/k heavy were determined to be kOH+CH3F/kOH+CD3F = 4.067 ± 0.018, kOH+CH3F/kOH+13CH3F = 1-067 ± 0.006, kCl+CH3F/kCl+CD3F = 5.11 ± 0.07, and kCl+CH3F/kCl+13CH3F = 1-016 ± 0.006. The carbon-13 and deuterium kinetic isotope effects in the OH and Cl reactions of CH3F have been further investigated by quantum chemistry methods and variational transition state theory.
- Marinkovic, Marina,Gruber-Stadler, Margret,Nicovich, J. Michael,Soller, Raenell,Muelhaeuser, Max,Wine, Paul H.,Bache-Andreassen, Lihn,Nielsen, Claus J.
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- chlorine atom initiated oxidation of chlorinated ethenes: Results for 1,1-dichloroethene (H2C=CCl2), 1,2-dichIoroethene (HClC=CClH), trichloroethene (HClC=CCl2), and tetrachloroethene (Cl2C=CCl2)
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Experiments have been carried out on the oxidation of the four chlorinated ethenes H2C=CCl2, HClC=CClH, HClC=CCl2, and Cl2C=CCl2. Reaction was initiated by continuous photolysis of Cl2, and
- Hasson, Alam S.
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- Some complexities in the reaction of hydrogen atoms generated in H2 discharge with molecular chlorine
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The kinetics of the reaction H + Cl2 → HCl + Cl was studied in the very low-pressure reactor system at 298 K using two different H atom generation sources. No traces of HCl(v) excited product side reaction could be found in the system due to th
- Benson,Dobis
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- Thermal Decomposition of Carbon Tetrachloride
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The first rate measurements of the thermal dissociation of CCl4 are reported.Three detection techniques were used in monitoring the reaction rate for various dilutions over a wide temperature range: (i) ARAS of product Cl atoms in reflected shock waves using 3.2-6.4 ppm of CCl4 in Ar over 1084-1705 K and 150-908 Torr, (ii) decay of CCl4 by molecular absorption of O-atom resonance radiation in reflected shock waves using 48 - 173 ppm of CCl4 in Ar over 1192 - 1733 K and 219 - 855 Torr, and (iii) laser schlieren density gradients in incident shock waves using 0.5 and 2 percent CCl4 in Kr over 1470 - 2186 K and 90 - 660 Torr.The second-order rates from ARAS and molecular absorption measurements for the bond fission reaction CCl4 -> CCl3 + Cl are in complete agreement with the laser schlieren results where they overlap.The temperature and pressure dependence of these rates is well characterized by Gorin model RRKM calculations using a current Δ H00 = 67.71 kcal/mol for E0, derived from ΔfH0298 = 17.0 kcal/mol for CCl3.The low-pressure rate constant (k0) derived from this RRKM fit is log k0 (cm3/mol s)) = 54.980 - 10.624 log T - 74.796 (kcal/mol)/2.303RT.These low-pressure rates require unusually large βc corresponding to a down = 1200 cm-1.This may be a general feature of chlorocarbon dissociations.The ARAS data indicate that two Cl atoms are ultimately produced for each CCl4 that dissociates, with second Cl atom forming slower than the first.Here all measurements are consistent with a further dissociation of CCl3, CCl3 -> CCl2 + Cl, as the dominant source of secondary Cl-atom at a rate about 0.1 that of the primary fission.
- Michael, J. V.,Lim, K. P.,Kumaran, S. S.,Kiefer, J. H.
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- Controlling the branching ratio of the photodissociation of aligned Cl2 at 404 nm
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Non-resonant infrared Nd3+:YAG laser pulses at 1.06 μm were used to align chlorine molecules in a cold molecular beam. The degree of alignment was demonstrated by measurement of the velocity anisotropy of the photofragment Cl(2P3/2) atoms from Cl2(X1Σg+)+404nm→Cl2 (B3Πu+,Ω=0)→Cl(2 P3/2)+Cl(2P1/2). The branching ratio of the photoexcitation to Cl2(B3Πu+,Ω=0) with respect to Cl2(1Πu,Ω=1) was controlled, allowing the selectivity of the two different adiabatic photodissociation channels: Cl(2P3/2)+Cl(2P1/2) and Cl(2P3/2)+Cl(2P3/2).
- Sugita, Akihiro,Suto, Kunihiro,Kawasaki, Masahiro,Matsumi, Yutaka
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- Photochemistry of phosgene in the solid phase: State-resolved dissociation dynamics
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The translational, rotational, and vibrational state distributions of CO (g) resulting from the single photon photodissociation of Cl2CO in the condensed phase at ~90 K have been determined by time-of-flight (TOF) distribution measurement and resonance-enhanced multiphoton ionization (REMPI) spectroscopy. The TOF distribution of CO (g) is bimodal. Internal state characterization of the slow channel reveals a completely thermalized origin, with a rotational temperature of Trot=88±5 K, which is equal to the translational temperature as well as the substrate temperature. We believe these slow CO molecules originate from photodissociation below the topmost surface of the molecular film and achieve thermal equilibrium with the substrate before escaping into the gas phase. Internal state characterization of the fast channel shows, on the other hand, an energetic origin: at hv=5.0 eV, the rotational distribution, with an overall flux-weighted mean rotational energy of 〈Erot〉=0.12±0.01 eV, is non-Boltzmann and can be approximated by a bimodal distribution with rotational temperatures of 210±40 K at low J″(s) and 2200±300 K at high J″(s); the relative vibrational population is Nv=1/Nv=0=0.33±0.05. Both rotational and translational distributions of fast CO show positive correlation with photon energy. These CO molecules must be promptly ejected into the gas phase, carrying nascent energetic information from the photodissociation reaction on the surface of the molecular film. For electronic excitation events that result in photodissociation, 74% of the excess excitation energy is distributed in the translational and internal motions of products (CO and Cl); only 26% of the available energy is converted to motions of surrounding molecules.
- Xin,Zhu
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- Photofragmentation study of Cl2 using ion imaging
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The Cl(2P3/2) and Cl(2P1/2) photofragments produced by the photolysis of Cl2 at ~3.5 eV, are detected using (3+1) and (2+1) resonance enhanced multiphoton ionization and their velocity distributions are measured using ion imaging. The measured photofragment translational energy distributions yield a bond dissociation energy of D0 = 2.474±0.020 eV for ground electronic state Cl2(X1Σg). The angular distributions yield anisotropy parameters of β(2P3/2) = - 0.87±0.05 and β(2P1/2)= 1.78 ±0.05 irrespective of the detection process. The branching ratio [Cl(2P1/2)]/[Cl(2P3/2)] is estimated at 8±1%.
- Samartzis, Peter C.,Sakellariou, Ioannis,Gougousi, Theodosia,Kitsopoulos, Theofanis N.
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- Kinetics of the reaction of the CH2Cl radical with oxygen atoms
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The kinetics of the reaction of CH2Cl with O(3P) has been investigated in a heatable tubular reactor coupled to a photoionization mass spectrometer. The decay of CH2Cl was monitored as a function of O atom concentration ([O]0/[CH2Cl]0 > 30) to determine the rate constant of the reaction as a function of temperature and pressure. The rate constant measured is independent of density and was fitted to an Arrhenius expression: k = (1.49 ± 0.35) × 10-10 exp[(1.46 ± 0.38) kJ mol-1/RT] cm3 molecule-1 s-1 over the temperature range 297-823 K. Both CHClO and CH2O were detected as products of the CH2Cl + O(3P) reaction. The production of CHClO is the major reaction channel.
- Seetula,Slagle
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- Selective C-H halogenation over hydroxylation by non-heme iron(iv)-oxo
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Non-heme iron based halogenase enzymes promote selective halogenation of the sp3-C-H bond through iron(iv)-oxo-halide active species. During halogenation, competitive hydroxylation can be prevented completely in enzymatic systems. However, synthetic iron(iv)-oxo-halide intermediates often result in a mixture of halogenation and hydroxylation products. In this report, we have developed a new synthetic strategy by employing non-heme iron based complexes for selective sp3-C-H halogenation by overriding hydroxylation. A room temperature stable, iron(iv)-oxo complex, [Fe(2PyN2Q)(O)]2+ was directed for hydrogen atom abstraction (HAA) from aliphatic substrates and the iron(ii)-halide [FeII(2PyN2Q)(X)]+ (X, halogen) was exploited in conjunction to deliver the halogen atom to the ensuing carbon centered radical. Despite iron(iv)-oxo being an effective promoter of hydroxylation of aliphatic substrates, the perfect interplay of HAA and halogen atom transfer in this work leads to the halogenation product selectively by diverting the hydroxylation pathway. Experimental studies outline the mechanistic details of the iron(iv)-oxo mediated halogenation reactions. A kinetic isotope study between PhCH3 and C6D5CD3 showed a value of 13.5 that supports the initial HAA step as the RDS during halogenation. Successful implementation of this new strategy led to the establishment of a functional mimic of non-heme halogenase enzymes with an excellent selectivity for halogenation over hydroxylation. Detailed theoretical studies based on density functional methods reveal how the small difference in the ligand design leads to a large difference in the electronic structure of the [Fe(2PyN2Q)(O)]2+ species. Both experimental and computational studies suggest that the halide rebound process of the cage escaped radical with iron(iii)-halide is energetically favorable compared to iron(iii)-hydroxide and it brings in selective formation of halogenation products over hydroxylation.
- Rana, Sujoy,Biswas, Jyoti Prasad,Sen, Asmita,Clémancey, Martin,Blondin, Geneviève,Latour, Jean-Marc,Rajaraman, Gopalan,Maiti, Debabrata
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p. 7843 - 7858
(2018/10/31)
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- Gas-Phase Reaction of Methyl n-Propyl Ether with OH, NO3, and Cl: Kinetics and Mechanism
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Rate constants at room temperature (293 ± 2 K) and atmospheric pressure for the reaction of methyl n-propyl ether (MnPE), CH3OCH2CH2CH3, with OH and NO3 radicals and the Cl atom have been determined in a 100 L FEP-Teflon reaction chamber in conjunction with gas chromatography-flame ionization detector (GC-FID) as the detection technique. The obtained rate constants k (in units of cm3 molecule-1 s-1) are (9.91 ± 2.30) × 10-12, (1.67 ± 0.32) × 10-15, and (2.52 ± 0.14) × 10-10 for reactions with OH, NO3, and Cl, respectively. The products of these reactions were investigated by gas chromatography-mass spectrometry (GC-MS), and formation mechanisms are proposed for the observed reaction products. Atmospheric lifetimes of the studied ether, calculated from rate constants of the different reactions, reveal that the dominant loss process for MnPE is its reaction with OH, while in coastal areas and in the marine boundary layer, MnPE loss by Cl reaction is also important.
- Zhu, Jianqiang,Wang, Shuyan,Tsona, Narcisse T.,Jiang, Xiaotong,Wang, Yifeng,Ge, Maofa,Du, Lin
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p. 6800 - 6809
(2017/09/23)
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- Measuring the rate constant of the reaction between chlorine atoms and CHF2Br by Cl atom resonance fluorescence
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The rate constant of the reaction between Cl atoms and CHF2Br has been measured by chlorine atom resonance fluorescence in a flow reactor at temperatures of 295–368 K and a pressure of ~1.5 Torr. Lining the inner surface of the reactor with F-32L fluoroplastic makes the rate of the heterogeneous loss of chlorine atoms very low (khet ≤ 5 s–1). The rate constant of the reaction is given by the formula k = (4.23 ± 0.13) × 10–12e(–15.56 ± 1.58)/RT cm3 molecule–1 s–1 (with the activation energy in kJ/mol units). The possible role of this reaction in the extinguishing of fires producing high concentrations of chlorine atoms is discussed.
- Larin,Spasskii,Trofimova,Proncheva
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p. 308 - 312
(2016/07/06)
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- Mechanism of thermal decomposition of allyltrichlorosilane with formation of three labile intermediates: dichlorosilylene, allyl radical, and atomic chlorine
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It is experimentally found that allyltrichlorosilane dissociates under vacuum pyrolysis (~10–2 Torr) at temperatures above 1100 K to form three labile intermediates: allyl radical, dichlorosilylene, and monoatomic chlorine. On the basis of experimental and theoretical data obtained, it is shown that the decomposition reaction proceeds in two steps. The first step is a typical reaction of homolytic decomposition to two radicals (C3H5 and SiCl3) at the weakest Si—C bond. Due to weakness of the Si—Cl bond in the SiCl3 radical, the energy of which is even somewhat lower than the dissociation energy of the Si—C bond in starting AllSiCl3, this radical undergoes further dissociation to SiCl2 and Cl, thus resulting in three intermediates of different classes of highly reactive species formed from AllSiCl3.
- Boganov,Promyslov,Krylova,Zaitseva,Egorov
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p. 1216 - 1224
(2017/02/05)
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- Atmospheric chemistry of CF3CH2OCH3: Reaction with chlorine atoms and OH radicals, kinetics, degradation mechanism and global warming potential
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FTIR smog chamber techniques were used to measure k(Cl + CF 3CH2OCH3) = (2.28 ± 0.44) × 10-11 and k(OH + CF3CH2OCH3) = (4.9 ± 1.3) × 10-13 cm3 molecule-1 s-1 in 700 Torr total pressure of air at 296 ± 2 K. The atmospheric lifetime of CF3CH2OCH3 is estimated at 25 days. Reaction of Cl atoms with CF3CH2OCH 3 proceeds 79 ± 4% at the CH3 group and 22 ± 2% at the CH2 group. Reaction with OH radicals proceeds 55 ± 5% at the CH3 group yielding CF3CH2OCHO and 45 ± 5% at the CH2 group yielding COF2 and CH 3OCHO as primary oxidation products. The infrared spectrum of CF 3CH(O)OCH3 was measured and a global warming potential GWP100 = 8 was estimated. The atmospheric chemistry and environmental impact of CF3CH2OCH3 is discussed in context of the use of hydrofluoroethers as CFC substitutes.
- ?sterstr?m, Freja From,Nielsen, Ole John,Sulbaek Andersen, Mads P.,Wallington, Timothy J.
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- Temperature (290-400 K) and pressure (5-900 Torr) dependence of the kinetics of the reactions of chlorine atoms with propene and 1-butene
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Rate constants for reactions of chlorine atoms with propene (k1) and 1-butene (k2) were measured relative to that of chlorine atoms with n-butane (k3) at 295-400 K in 5-900 Torr of N2 using gas chromatographic a
- Kaiser,Wallington
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p. 187 - 192
(2011/02/28)
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- Dynamics of Cl (2Pj) atom formation in the photodissociation of fumaryl chloride (ClCO - CH = CH - COCl) at 235 nm: A resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) study
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The photodissociation dynamics of fumaryl chloride (ClCO-CH=CH-COCl) has been studied in a supersonic molecular beam around 235 nm using resonance enhanced multiphoton ionization (REMPI) time-of-flight (TOF) technique by detecting the nascent state of the primary chlorine atom. A single laser has been used for excitation of fumaryl chloride and the REMPI detection of chlorine atoms in their spin-orbit states, Cl (2P3/2) and Cl* (2P1/2). We have determined the translational energy distribution, the recoil anisotropy parameter, β, and the spin-orbit branching ratio for chlorine atom elimination channels. To obtain these, measured polarization-dependent and state-specific TOF profiles are converted into kinetic energy distributions, using a least-squares fitting method, taking into account the fragment recoil anisotropies, βi. The TOF profiles for both Cl and Cl* are found to be independent of laser polarization; i.e., β is well characterized by a value of 0.0, within the experimental uncertainties. Two components, namely, the fast and the slow, are observed in the translational energy distribution, P(ET), of Cl and Cl* atoms, and assigned to be formed from different potential energy surfaces. The average translational energies for the fast components of the Cl and Cl* channels are 14.9 ± 1.6 and 16.8 ± 1.6 kcal/mol, respectively. Similarly, for the slow components, the average translational energies of the Cl and Cl* channels are 3.4 ± 0.8 and 3.1 ± 0.8 kcal/mol, respectively. The energy partitioning into the translational modes is interpreted with the help of various models, such as impulsive and statistical models. Apart from the chlorine atom elimination channel, molecular hydrogen chloride (HCl) elimination is also observed in the photodissociation process. The HCl product has been detected, using a REMPI scheme in the region of 236-237 nm. The observation of the molecular HCl in the dissociation process highlights the importance of the relaxation process, in which the initially excited parent molecule relaxes to the ground state from where the molecular (HCl) elimination takes place.
- Kawade, Monali,Saha, Ankur,Upadhyaya, Hari P.,Kumar, Awadhesh,Naik, Prakash D.,Bajaj
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p. 1538 - 1546
(2011/05/07)
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- PLP-LIF study of the reactions of chlorine atoms with C2H 2, C2H4, and C3H6 in 2-100 Torr of N2 diluent at 295 K
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Pulsed laser photolysis-laser-induced fluorescence (PLP-LIF) techniques were used to study the reactions of Cl(2P3/2) atoms with C2H2 (k1), C2H4 (k 2), and C3/su
- Iwasaki, Erika,Chiba, Hitoshi,Nakayama, Tomoki,Matsumi, Yutaka,Wallington, Timothy J.
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p. 174 - 178
(2010/09/17)
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- Kinetics of the reaction of Cl atoms with CHCl3 over the temperature range 253-313 K
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The reaction CHCl3 + Cl → CCl3 + HCl was studied in the atmospherically relevant temperature range from 253 to 313 K and in 930 mbar of N2 diluent using the relative rate method. A temperature dependent reaction rate constant, valid in the temperature range 220-330 K, was determined by a fit to the result of the present study and that of Orlando (1999); k = (3.77 ± 0.32) × 10-12 exp((-1011 ± 24)/T) cm3 molecule-1 s-1.
- Nilsson, Elna J.K.,Hoff, Janus,Nielsen, Ole John,Johnson, Matthew S.
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p. 160 - 162
(2010/09/17)
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- Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation
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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.
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- Chlorine-catalyzed ozone destruction: Cl atom production from ClOOCl photolysis
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Recent laboratory measurements of the absorption cross sections of the ClO dimer, ClOOCl, have called into question the validity of the mechanism that describes the catalytic removal of ozone by chlorine. Here we describe direct measurements of the rate-d
- Wilmouth, David M.,Hanisco, Thomas F.,Stimpfle, Richard M.,Anderson, James G.
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p. 14099 - 14108
(2010/06/12)
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- Atmospheric chemistry of 3-pentanol: Kinetics, mechanisms, and products of Cl atom and OH radical initiated oxidation in the presence and absence of NOx
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Smog chamber/FTIR techniques were used to study the atmospheric chemistry of 3-pentanol and determine rate constants of k(Cl+3-pentanol) = (2.03 ± 0.23) × 10-10 and k(OH+3-pentanol) = (1.32 ± 0.15) × 10-11 cm3 moleculesup
- Hurley,Wallington,Bjarrum,Javadi,Nielsen
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p. 8053 - 8060
(2009/04/13)
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- Adiabatic and nonadiabatic dynamics in the C H3 (CD3) +HCl reaction
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The scattering dynamics leading to the formation of Cl (P 32 2) and Cl* (P 12 2) products of the C H3 +HCl reaction (at a mean collision energy ? Ecoll ? =22.3 kcal mol-1) and the Cl (P 32 2) products of the C D3 +HCl reaction (at ? Ecoll ? =19.4 kcal mol-1) have beeninvestigated by using photodissociation of C H3 I and C D3 I as sources of translationally hot methyl radicals and velocity map imaging of the Cl atom products. Image analysis with a Legendre moment fitting procedur e demonstrates that, in all three reactions, the Cl Cl* products are mostly forward scattered with respect to the HCl in the center-of-mass (c.m.) frame but with a backward scattered component. The distributions of the fraction of the available energy released as translation peak at ft =0.31-0.33 for all the reactions, with average values that lie in the range ? ft ? =0.42-0.47. The detailed analysis indicates the importance of collision energy in facilitating the nonadiabatic transitions that lead to Cl* production. The similarities between the c.m.-frame scattering and kinetic energy release distributions for Cl and Cl* channelssuggest that the nonadiabatic transitions to a low-lying excited potent ial energy surface (PES) correlating to Cl* products occur after passagethrough the transition state region on the ground-state PES. Branching fractions for Cl* are determined to be 0.14±0.02 for the C H3 +HC l reaction and 0.20±0.03 for the C D3 +HCl reaction. The difference cannot be accounted for by changes in collision energy, mass effects,or vibrational excitation of the photolytically generated methyl radica l reagents and instead suggests that the low-frequency bending modes of the C D3 H or C H4 coproduct are important mediators of the nonadiabaticcouplings occurring in this reaction system.
- Retail, Bertrand,Pearce, Julie K.,Greaves, Stuart J.,Rose, Rebecca A.,Orr-Ewing, Andrew J.
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- Mechanism of the gas phase reaction of chlorine atoms with butanone
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Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of CH3C(O)CH2CH3 in 700-760 Torr of N2 at 296 K. The reaction of Cl atoms with CH3C(O)CH2CH3 proceeds via hydrogen abstraction with 73 ± 9% of reaction occurring at the -CH2- group. Relative rate techniques were used to measure k(Cl + CH3C(O)CHClCH3) = (5.62 ± 0.81) × 10-12 cm3 molecule-1 s-1. It was deduced that the CH3C(O)CHCH3 radical reacts with Cl2 with a rate constant of the order of 10-14 to 10-13 cm3 molecule-1 s-1.
- Iwasaki,Taketani,Takahashi,Matsumi,Wallington,Hurley
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p. 274 - 279
(2008/10/09)
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- Kinetic study of the ClOO + NO reaction using cavity ring-down spectroscopy
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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.
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p. 3546 - 3551
(2008/10/09)
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- Kinetic study of the collisional quenching of spin-orbitally excited atomic chlorine, Cl(2P1/2), by H2O, D2O, and H2O2
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Rate constants for the collisional quenching of spin-orbitally excited Cl(2P1/2) atoms by H2O, D2O, and H2O2 were determined at ~295 K using laser-flash photolysis and laser-induced fluores
- Kono, Mitsuhiko,Takahashi, Kenshi,Matsumi, Yutaka
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- Kinetics of the gas-phase reaction of OH with HCl
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The reaction of hydroxyl radicals with hydrogen chloride (reaction 1) has been studied experimentally using a pulsed-laser photolysis/pulsed-laser-induced fluorescence technique over a wide range of temperatures, 298-1015 K, and at pressures between 5.33 and 26.48 kPa. The bimolecular rate coefficient data set obtained for reaction 1 demonstrates no dependence on pressure and exhibits positive temperature dependence that can be represented with modified three-parameter Arrhenius expression within the experimental temperature range: k1 = 3.20 × 10-15T0.99 exp(-62 K/T) cm3 molecule-1 s-1. The potential-energy surface has been studied using quantum chemical methods, and a transition-state theory model has been developed for the reaction 1 on the basis of calculations and experimental data. The model results in modified three-parameter Arrhenius expressions: k1 = 8.81 × 10-16T1.6 exp(58 K/T) cm3 molecule-1 s-1 for the temperature range 200-1015 K and k1 = 6.84 × 10-19T 2.12 exp(646 K/T) cm3 molecule-1 s-1 for the temperature dependence of the reaction 1 rate coefficient extrapolation to high temperatures (500-3000 K). A temperature dependence of the rate coefficient of the Cl + H2O → HCl + OH reaction has been derived on the basis of the experimental data, modeling, and thermochemical information.
- Bryukov, Mikhail G.,Dellinger, Barry,Knyazev, Vadim D.
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p. 936 - 943
(2008/10/09)
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- Femtosecond pump-probe studies of nitrosyl chloride photochemistry in solution
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We present a femtosecond pump-probe study of the primary events of nitrosyl chloride (ClNO) photochemistry in solution. Following 266 nm photolysis, the resulting evolution in optical density is measured for ClNO dissolved in acetonitrile, chloroform, and dichloromethane. The results demonstrate that photolysis results in the production of a photoproduct that has an absorption band maximum at 295 nm in acetonitrile and 330 nm in chloroform and dichloromethane. To determine the extent of Cl production, comparative photochemical studies of methyl hypochlorite (MeOCl) and C1NO are performed. Photolysis of MeOCl in solution results in the production of the Cl:solvent charge-transfer complex; therefore, a comparison of the spectral evolution observed following MeOCl and ClNO photolysis under identical photolysis conditions is performed to determine the extent of Cl production following ClNO photolysis. We find that similar to the gas-phase photochemistry, Cl and NO formation is the dominant photochemical channel in acetonitrile. However, the photochemistry in chloroform and dichloromethane is more complex, with a second product formed in addition to Cl and NO. It is proposed that in these solvents photoisomerization also occurs, resulting in the production of ClON. The results presented here represent the first detailed examination of the solution phase photochemistry of ClNO.
- Cooksey, Catherine C.,Johnson, Kevin J.,Reid, Philip J.
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p. 8613 - 8622
(2008/10/09)
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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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- Reactions of POxCly-ions with H and H 2 from 298 to 500 K
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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
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p. 2559 - 2563
(2008/03/12)
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- A selected ion flow tube study of the reactions of gas-phase cations with PSCl3
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A selected ion flow tube was used to investigate the positive ion chemistry of thiophosphoryl chloride, PSCl3. Rate coefficients and ion product branching ratios have been determined at room temperature for reactions with 19 cations; H3O+, CF3+, CF +, NO+, NO2+, SF2 +, SF+, CF2+, O2 +, H2O+, N2O+, O +, CO2+, CO+, N+, N 2+, Ar+, F+ and Ne+ (in order of increasing recombination energy). Complementary data described in the previous paper have been obtained for this molecule via the observation of threshold photoelectron photoion coincidences. For ions whose recombination energies are in the range 10-22 eV, comparisons are made between the product ion branching rations of PSCl3 from photoionisation and from ion-molecule reactions. In most instances, the data from the two experiments are well correlated, suggesting that long-range charge transfer is the dominant mechanism for these ion-molecule reactions; the agreement is particularly good for the atomic ions Ar+, F+ and Ne+. Some reactions (e.g. O2++PSCl3), however, exhibit significant differences; short-range charge transfer must then be occurring following the formation of an ion-molecule complex. For ions whose recombination energies are less than 10 eV (i.e. H3O+, CF 3+, CF+ and NO+), reactions can only occur via a chemical process in which bonds are broken and formed, because the recombination energy of the cation is less than the ionisation energy of PSCl3.
- Critchley, Andrew D.J.,Howle, Chris R.,Mayhew, Chris A.,Tuckett, Richard P.
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p. 235 - 241
(2008/10/09)
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- The Cl to NCl branching ratio in 248-nm photolysis of chlorine azide
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The primary reaction products from 248-nm chlorine azide photolysis are identified in a collision-free experiment. In contrast to all previous reports, the radical channel producing Cl+N3 (95±3%) is seen to dominate the photochemistry. The molecular channel producing NCl+N2 (5±3%) was also observed.
- Wodtke, Alec M.,Hansen, Nils,Robinson, Jason C.,Sveum, Niels E.,Goncher, Scott J.,Neumark, Daniel M.
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p. 334 - 337
(2008/10/09)
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- Temperature Dependence of the Rate Constant for the Reaction F( 2P) + Cl2 → FCl + Cl at T = 180-360 K
-
The absolute rate constant for the reaction F(2P) with Cl 2 has been measured using the discharge flow kinetics technique coupled to mass spectrometric detection at T = 180-360 K and 1 Torr He nominal pressure. Experiments were performed at NASA Goddard Space Flight Center (GSFC) in Greenbelt, MD, and Laboratoire de Combustion et Systemes Reactifs-CNRS in Orleans, France. Results of k = (5.7 ± 0.8) × 10-11 and (6.2 ± 0.8) × 10-11 cm3 molecule-1 s-1 independent of temperature were obtained by each laboratory, respectively. When the results from both laboratories were combined into one data set, an average temperature independent value of k1 = (6.0 ± 1.1) × 10-11 cm3 molecule-1 s-1 was obtained. A very slight positive temperature dependence with k1(T) = (6.5 ± 1.5) × 10-11 exp{-(20 ± 60)/T} cm3 molecule-1 s-1 may also be derived from the combined data in the range T = 180-360 K.
- Nesbitt, Fred L.,Cody, Regina J.,Dalton, Douglas A.,Riffault, Veronique,Bedjanian, Yuri,Le Bras, Georges
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p. 1726 - 1730
(2007/10/03)
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- Ultraviolet photolysis of the ClO dimer
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Photodissociation of the ClO dimer (ClOOCl) is studied in the ultraviolet regime (250 and 308 nm) under collision-free conditions. The primary photolysis products are probed by photoionization mass spectrometry. At both photolysis wavelengths, exclusively the formation of 2Cl + O2 is observed, corresponding to a primary quantum yield γCl near unity. Considering the error limit of the experimental results one obtains γCl ≥ 0.98 at 250 nm and γCl ≥ 0.90 at 308 nm, respectively. At both photolysis wavelengths the pathway yielding ClO is not observed, corresponding to γClO ≤ 0.02 at 250 nm and γClO ≤ 0.10 at 308 nm. Sensitivity studies of these results with respect to ozone depletion in the stratosphere regarding photochemically induced ozone loss are discussed using model simulations. These simulations suggest that a change of γCl from 1.0 to 0.9 leads to a reduction of polar ozone loss of ~5%.
- Plenge,Flesch,Kuehl,Vogel,Mueller,Stroh,Ruehl
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p. 4859 - 4863
(2007/10/03)
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- Kinetic studies of the Cl + HI reaction using three techniques
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The reaction Cl + HI → HCl + I was investigated using the laser-photolysis/resonance fluorescence method to monitor (i) the disappearance of atomic Cl and (ii) the growth of atomic I. The results were similar, and together yield the rate constant k = (3.4 ± 1.4) × 10-11 exp (+2.8±1.1 kJ mol-1/RT) cm3 molecule -1s-1 (1σerrors) over 297-390 K. The 95% confidence limits for k are ±19%. Another approach, discharge/fast-flow (iii), with monitoring of the consumption of Cl in the presence of excess HI, yields k = 1.2 × 10-10 cm3 molecule-1 s-1 at 298 K, with 95% confidence limits of ±17%. The results are in accord with each other and with most literature data. This indicates that monitoring of the formation of the atomic halogen product in this example of a radical abstraction of H from a hydrogen halide is reliable.
- Yuan, Jessie,Misra, Ashutosh,Goumri,Shao, Diane D.,Marshall, Paul
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p. 6857 - 6862
(2007/10/03)
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- Relative reaction rates of HCHO, HCDO, DCDO, H13CHO, and HCH18O with OH, Cl, Br, and NO3 radicals
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Formaldehyde (HCHO) is a principal intermediate in the photochemical oxidation of hydrocarbons in the troposphere. Isotopic analysis is an important tool for tracing the atmospheric path of gaseous species, and for this purpose, characterization of the isotope effects in the loss processes for formaldehyde is needed. The main loss pathways for formaldehyde in the atmosphere are photolysis and reactions with the radical species of OH, Cl, Br, and NO 3. In this study, the kinetic isotope effects in the reactions of five different isotopomers of formaldehyde (HCHO) with OH, Cl, Br, and NO 3 radicals are studied in a relative-rate experiment at 298 ± 2 K and 1013 ± 10 mbar. The reaction rates of DCDO, HCDO, H 13CHO, and HCH18O with the four radicals are measured relative to H2CO in a smog chamber using long-path FTIR detection. The experimental data are analyzed with a nonlinear least-squares spectral-fitting method using measured high-resolution infrared spectra and cross sections from the HITRAN database. The reaction rates of HCDO and HCH 13O with OH and Cl are determined relative to HCHO as k OH+HCHO/kOH+HCDO = 1.28 ± 0.01, k OH+HCHO/kOH+HCH18O = 0.967 ± 0.006, k Cl+HCHO/kCl+HCDO = 1.201 ± 0.002, and k Cl+HCHO/kCl+HCH18O = 1.08 ± 0.01. The reaction rates of HCDO and HCH18O with Br and NO3 are determined relative to HCHO as kBr+HCHO/kBr+HCDO = 3.27 ± 0.03, k Br+HCHO/kBr+HCH18O = 1.275 ± 0.008, k NO3+HCHO/kNO3+HCDO = 1.78 ± 0.01, and k NO3+HCHO/kNO3+HCH18O = 0.98 ± 0.01. The errors represent 2σ from the statistical analyses, and do not include possible systematic errors.
- Fellberg, Karen L.,Johnson, Matthew S.,Nielsen, Claus J.
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p. 7393 - 7398
(2007/10/03)
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- I*(2P1/2) and Cl*(2P 1/2) production from chloroiodobenzenes in the ultraviolet
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The relative quantum yields of I*(2P1/2) and Cl*(2P1/2) production, φ(I) and φ*(Cl), respectively, have been measured at four different ultraviolet excitation wavelengths, e.g., 222, 236, 266, and 280 nm in the
- Senapati, Dulal,Maity, Sandip,Das, Puspendu K.
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p. 7949 - 7953
(2008/04/18)
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- Measurement of Br photofragment orientation and alignment from HBr photodissociation: Production of highly spin-polarized hydrogen atoms
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The use of slice imaging to measure the orientation and alignment of 2P3/2 and 2P1/2 photofragments at 193 nm in terms of polarization parameters, aqk(p) parameters, was described. The photofragments were obtained from the photodissociation of HBr. It was found that the photodissociation was a source of spin-polarized hydrogen. The spin-orbit branching ratio and the polarization parameters showed that the photodissociation proceeded predominantly via nonadiabatic transition to the a3π and 13∑+ states. It was also found that the electrons of the nascent H atom cofragments were highly spin polarized.
- Rakitzis, T. Peter,Samartzis,Toomes,Kitsopoulos, Theofanis N.
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p. 7222 - 7227
(2007/10/03)
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- 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
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p. 9120 - 9125
(2008/10/09)
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- Detection of CISO with time-resolved Fourier-transform infrared absorption spectroscopy
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A step-scan Fourier-transform infrared spectrometer was used to detect time-resolved spectrum of ClSO. The rotational structure with the Q-branch at 1162.9 cm-1 was revealed by a spectrum with a resolution of 0.3 cm-1. The geometry, vibrational and rotational parameters of ClSO were predicted by calculations with density-functional theory. The results show that the CISO produced from photolysis of Cl2SO at 248 nm is internally hot.
- Chu, Li-Kang,Lee, Yuan-Pern,Jiang, Eric Y.
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p. 3179 - 3184
(2007/10/03)
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- Femtosecond pump-probe studies of dichlorine monoxide in solution
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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.
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p. 5508 - 5514
(2007/10/03)
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- Experimental evidence for acceleration of reaction between iodine monoxide and chlorine monoxide at the reactor surface
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The reaction of iodine monoxide with chlorine monoxide resulting in atom escape to the gas phase is studied at T = (303 ± 5) K and P = 2.5 Torr using a flow setup for measuring the resonance fluorescence signals of atomic iodine and chlorine. The heterogeneous reaction between chlorine monoxide and iodine monoxide occurring at the reactor surface covered with an F32-L Teflon-like compound and treated by the reaction products is characterized by the rate constant k = (4.9 ± 0.2) x 10-11 cm3 molecule-1 s-1. This value is substantially higher than the rate constant for the homogeneous reaction IO. + ClO. (k1 ≤ 1 x 10-12 cm3 molecule-1 s-1).
- Larin,Spasskii,Trofimova,Turkin
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p. 202 - 210
(2008/10/08)
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- Absolute chlorine atom quantum yield measurements in the UV and VUV gas-phase laser photolysis of CCl4
-
Among the chlorinated and fluorinated methanes involved in the stratospheric ozone destruction, CCl4 has the highest ozone depletion potential. Absolute quantum yields ΦCl+Cl* for the formation of chlorine atoms were measured under collision-free conditions for the gas-phase dissociation of CCl4 after pulsed laser photoexcitation at 193 and 135 nm. By means of a photolytic calibration method, where the gas-phase photolysis of HCl was utilized as a reference, values of ΦCl+Cl* (193 nm)= 1.5 ± 0.1 and ΦCl+Cl* (135 nm)= 1.9 ± 0.1 could be obtained, which demonstrate the importance of the UV and vacuum-UV photolysis of CCl4 as an efficient source of atomic chlorine formation.
- Hanf, Alexander,Laeuter, Almuth,Volpp, Hans-Robert
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p. 445 - 451
(2008/10/08)
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- Femtosecond photolysis of HOCl(aq): Dissipation of fragment kinetic energy
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In this work, we present an experimental study of the energy dependence of the photolysis of aqueous HOCl and the subsequent recombination of the OH and Cl photofragments. Using femtosecond transient absorption spectroscopy, we follow the time-dependent concentration of the fragments. The excess energy in the photolysis is given to the fragments as kinetic energy, and tuning the wavelength enables a study of the energy-dependent thermalization and geminate recombination of the fragments in the liquid environment. The recombination yield and rate are governed by the initial fragment separation, and we deduce an approximately linear dependence of the fragment separation versus the kinetic energy with a slope of 0.13 nm/eV. Performing a simple MD simulation of the system gives qualitative agreement with the observations, although the calculated slope is only 0.04 nm/eV.
- Madsen,Thomsen,Poulsen,Knak Jensen,Thoogersen,Keiding,Krissinel
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p. 3606 - 3611
(2007/10/03)
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- Photodissociation of gaseous NCl3 at 193 and 249 nm
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The optical absorption spectrum of gaseous NCl3 was measured from 170 to 350 nm, and experiments were performed in which this molecule was irradiated with a pulsed laser at 193 nm and 249 nm. Photodissociation channels accessible at these wavelengths can produce fragments in singlet, doublet, or triplet manifolds of states. Photodissociation at 249 nm produces prompt banded emission in the visible and near-IR spectral regions that is tentatively ascribed to transitions in NCl2, suggesting that the dissociation channel leading to doublet fragments (NCl2 and Cl) is operative at this photolysis wavelength. The absence of emission from excited singlet states of NCl or excited triplet states of Cl2 suggests that the singlet and triplet dissociation channels are not important at 249 nm. For photolysis at 193 nm, prompt emission is observed from both the a1Δ and b1Σ+ excited states of NCl. No emission is observed from either NCl2 or excited triplet states of Cl2. A measure of the quantum yield for NCl(a1Δ) production by the 193 nm photodissociation of NCl3 was determined by observing the transfer of energy from excited NC1 to iodine atoms in the pulsed photolysis system. This method suggests that the yield has a value of 0.8 ± 0.2.
- Coombe,Gilbert,Beaton,Mateljevic
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p. 8422 - 8426
(2007/10/03)
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- Photoionization of the primary photoproducts of A(2∏)-excited CIO
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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
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p. 9663 - 9670
(2007/10/03)
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- Gas-phase reactions of chlorine atoms and CIO radicals with dimethyl sulfide. Rate coefficients and temperature dependences
-
The results of a discharge flow-mass spectrometric (DF-MS) kinetic study of the reaction between Cl and dimethylsulfide (DMS) (1) over the temperature range 259-364 K at low total pressure between 0.5 and 1 Torr with helium as carrier gas are reported. At room temperature and 1.0 Torr the main products of reaction 1 correspond to an abstraction channel leading to HCl and CH3SCH2 with k(1) = (6.9 ± 1.3) × 10-11 cm3 molecule-1 s-1. The association channel has also been confirmed by mass spectroscopic detection of the adduct CH3S(Cl)CH3 with a yield a slight activation energy, k(1) = (2.0 ± 1.2) × 10-10 exp[-(332 ± 173)/T] cm3 molecule-1 s-1 The kinetics and mechanism of the reaction ClO + DMS → products (2) over the temperature range 259-335 K at total pressures between 0.5 and 2 Torr have also been studied by DF-MS. By mass spectroscopic calibration of dimethyl sulfoxide, DMSO, the branching ratio of the channel leading to this product has been measured (0.90 ± 0.49). The rate constant of reaction 2 has been measured under pseudo-first-order conditions in excess of DMS over ClO: k(2) = (1.2 ± 0.7) × 10-15 exp[(354 ± 163)/T] cm3 molecule-1 s-1 with k(2) = (3.9 ± 1.2) × 10-15 cm3 molecule-1 s-1 at 298 K. The reaction is postulated to proceed through a channel involving a long-lived intermediate [CH3S(OCl)CH3]* which may decompose back to reactants or to products. Finally, the atmospheric implications through the DMS chemistry of both reactions are discussed.
- Diaz-de-Mera,Aranda,Rodriguez,Lopez,Cabanas,Martinez
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p. 8627 - 8633
(2007/10/03)
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- Experimental and theoretical studies of the rate coefficients of the reaction O(3P) + HCl at high temperatures
-
Rate coefficients of the reaction O(3P) + HCl in the temperature range 1093-3197 K were determined using a diaphragmless shock tube. O atoms in the ground electronic 3P states were generated either by photolysis of SO2 with a KrF excimer laser at 248 nm or by pyrolysis of N2O with the shock wave. Their concentrations were monitored via atomic resonance absorption excited by emission from a microwave-discharged mixture of O2 and He. Rate coefficients determined in this work show non-Arrhenius behavior, with values consistent with previously reported measurements for T 1(T) = (9.27 ± 0.03) × 10-24 T3.67±0.18 exp[-(1030 ± 160)/T] cm3 molecule-1 s-1; listed errors represent one standard deviation in fitting. Theoretical calculations at the CCSD(T)/6-311+G(d, p) level locate a bent 3A″ (TS1) and a linear 3A′ (TS3) transition state characterized previously. On the basis of the results computed by CCSD(T)/ 6-311+G(3df,2p)//CCSD(T)/6-311+G(d,p), the rate coefficients predicted with conventional transition-state theory, including Eckart-tunneling corrections and with variational transition-state theory including zero- and small-curvature tunneling corrections, all agree satisfactorily with experimental observations.
- Hsiao, Chih-Chang,Lee, Yuan-Pern,Wang, Niann S.,Wang,Lin
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p. 10231 - 10237
(2007/10/03)
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- Hydrogen atom reactions with molecular halogens: The rate constants for H + F2 and H + Cl2 at 298 K
-
The rate constants for H atom reactions with Cl2 and F2 have been measured by monitoring the loss rate of hydrogen atoms in the presence of excess [Cl2] and [F2] via time-resolved, laser-induced Lyman-α fluoresc
- Han, Jiande,Heaven, Michael C.,Manke II, Gerald C.
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p. 8417 - 8421
(2007/10/03)
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- Fourier moment analysis of velocity-map ion images
-
A new method for extracting velocity and angular momentum distributions from velocity-map ion images was developed. The technique was demonstrated by using it to analyze sets of images from two different photolysis processes. The potential of the method for application to bimolecular reactions was illustrated using simulated images based on the results of recent quantum scattering calculations on the reaction H+D2→HD(v=0,j=0,9)+D.
- Bass, Mark J.,Brouard, Mark,Clark, Andrew P.,Vallance, Claire
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p. 8723 - 8735
(2007/10/03)
-