Kinetics of the reaction Cl + NO2 + M

The termolecular rate constant for the reaction Cl + NO₂ + M has been measured over the temperature range 264 to 417 K and at pressure 1 to 7 torr in a discharge flow system using atomic chlorine resonance fluorescence at 140 nm to monitor the decay of Cl in an excess of NO₂. The results are\documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm He}} = 9.4{\rm } \times {\rm }10^{ - 31} \left({\frac{T}{{300}}} \right)^{ - 2.0 \pm 0.05} {\rm cm}^6 {\rm s}^{ - {\rm 1}}$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$k_1^{{\rm N}2} = (14.8{\rm } \pm {\rm }1.4){\rm } \times {\rm 10}^{ - 31} {\rm cm}^6 {\rm s}^{ - 1}$\end{document} at 296 K where error limits represent one standard deviation. The systematic error of k₁ measurements is estimated to be about 15%. Using a static photolysis system coupled with the FTIR spectrophotometer the branching ratio for the formation of the two possible isomers was found to be ClONO(?75%) and CINO₂(?25%) in good agreement with previous measurements.     

Kinetics and mechanism of the reaction of Cl atoms with CH2 CO (Ketene)

The kinetics and mechanism of the gas-phase reaction of Cl atoms with CH₂CO have been studied with a FTIR spectrometer/smog chamber apparatus. Using relative rate methods the rate of reaction of Cl atoms with ketene was found to be independent of total pressure over the range 1–700 torr of air diluent with a rate constant of (2.7 ± 0.5) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ at 295 K. The reaction proceeds via an addition mechanism to give a chloroacetyl radical (CH₂ClCO) which has a high degree of internal excitation and undergoes rapid unimolecular decomposition to give a CH₂Cl radical and CO. Chloroacetyl radicals were also produced by the reaction of Cl atoms with CH₂ClCHO; no decomposition was observed in this case. The rates of addition reactions are usually pressure dependent with the rate increasing with pressure reflecting increased collisional stabilization of the adduct. The absence of such behavior in the reaction of Cl atoms with CH₂CO combined with the fact that the reaction rate is close to the gas kinetic limit is attributed to preferential decomposition of excited CH₂ClCO radicals to CH₂Cl radicals and CO as products as opposed to decomposition to reform the reactants. As part of this work ab initio quantum mechanical calculations (MP2/6-31G(d,p)) were used to derive Δ_fH₂₉₈(CH₂ClCO) = −(5.4 ± 4.0) kcal mol⁻¹. © 1996 John Wiley & Sons, Inc.     

Kinetics and mechanism of the reaction of Cl atoms with HO2 radicals

The kinetic and mechanism of the reaction Cl + HO₂ → products (1) have been studied in the temperature range 230–360 K and at total pressure of 1 Torr of helium using the discharge‐flow mass spectrometric method. The following Arrhenius expression for the total rate constant was obtained either from the kinetics of HO₂ consumption in excess of Cl atoms or from the kinetics of Cl in excess of HO₂: k₁ = (3.8 ± 1.2) × 10^?11 exp[(40 ± 90)/T] cm³ molecule^?1 s^?1, where uncertainties are 95% confidence limits. The temperature‐independent value of k₁ = (4.4 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 at T = 230–360 K, which can be recommended from this study, agrees well with most recent studies and current recommendations. Both OH and ClO were detected as the products of reaction (1) and the rate constant for the channel forming these species, Cl + HO₂ → OH + ClO (1b), has been determined: k_1b = (8.6 ± 3.2) × 10^?11 exp[?(660 ± 100)/T] cm³ molecule^?1 s^?1 (with k_1b = (9.4 ± 1.9) × 10^?12 cm³ molecule^?1 s^?1 at T = 298 K), where uncertainties represent 95% confidence limits. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 317–327, 2001     

Rate constant and products of the reaction Cl + CS2 in air

A steady-state system involving the photolysis of Cl₂ as a source of Cl has been used to investigate the reaction of Cl with CS₂ at 293 ± 3 K in a 420 l reaction chamber coupled to FTIR and mass spectrometers. Using a relative rate technique, the measured effective rate constant was found to be dependent on the total pressure and mole fraction of O₂ present in the system. In 760 Torr synthetic air, the overall rate constant for the Cl + CS₂ reaction is(0.83 ± 0.17) × 10⁻¹³ cm³ molecule⁻¹s⁻¹. SO₂, COS and COCl₂ are the main reaction products.     

Kinetics and mechanism of the gas phase reaction of Cl atoms with iodobenzene

Smog chamber/FTIR techniques were used to study the kinetics and mechanism of the reaction of Cl atoms with iodobenzene (C₆H₅I) in 20–700 Torr of N₂, air, or O₂ diluent at 296 K. The reaction proceeds with a rate constant k(Cl+C₆H₅I)=(3.3±0.7)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹ to give chlorobenzene (C₆H₅Cl) in a yield which is indistinguishable from 100%. The title reaction proceeds via a displacement mechanism (probably addition followed by elimination).     

Kinetics and mechanism of the OH + CIO2reaction

The rate constant k₁ for the reaction of OH radicals with CIO₂ molecules was measured in a discharge flow system over the temperature range 293 ≤ T ≤ 473 K and at low pressures, 0.5 ≤ P ≤ 1.4 torr, using electron paramagnetic resonance or laser-induced fluorescence to monitor the pseudo first-order decay of OH concentrations. At 293 K, the value obtained for k₁ was (7.2 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1. Within the temperature range of this study, a negative temperature dependence was observed: k₁ = (4.50 ± 0.75) × 10^?13 exp[(804 ± 114)/T] cm³ molecule^?1 s^?1. HOCl was detected by mass spectrometry as a product of the reaction and was titrated using OH + Cl₂ as a source in the calibration experiments. A simulation of the mechanism of the OH + ClO₂ reaction indicated that HOCl was mainly produced in the first reaction step. Both this result and the observed T dependence of k₁ suggest that this reaction proceeds via an intermediate adduct with a cyclic geometry.     

A diode laser study of the Cl + CH3CO reaction

Real-time kinetic measurements are reported for the Cl + CH₃CO → CH₂CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10–200 torr and a temperature range of 215–353 K. Within experimental error the rate constant under these conditions is k_5a = (1.8 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹. We have also examined the Cl + CH₂CO reaction and found it to have a rate constant of k₆ = (2.5 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹ independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421–429, 1997.     

Kinetics and mechanism of the reaction H + CH3ONO

The reaction of hydrogen atoms with methyl nitrite was studied in a fast-flow system using photoionization mass spectrometry and excess atomic hydrogen. The associated bimolecular rate coefficient can be expressed by in the temperature range of 223-398°K. NO, CH₃OH, CH₄, C₂H₆, CH₂O, and H₂O are the main products; OH and CH₃ radicals were detectable intermediates. The mechanism was deduced from the observed product yields using normal and deuterated reactants. The primary reaction steps were identified as followed by a rapid unimolecular decomposition of CH₂ONO into CH₂O and NO. Since the extent of reaction channel (1b) could not be determined independently, only extreme limits could be obtained for the individual contributions of the two channels of reaction (3) which follows the generation of CH₃O radicals: The most probable values, k_3a/k₃ = 0.31 ± 0.30 and k_3b/k₃ = 0.69 ± 0.30, support the previous results on this reaction, although the range of uncertainties is much greater here.     

Kinetics and mechanism of the solid state reaction TlCl + KI → TlI + KCl

The kinetics of the solid state displacement reaction TlCl + KI → TlI + KCl was investigated by the diffusion couple method (using single crystal disks and pellets) in the temperature range 215–300°C. Two distinct layers are present: the first, in contact with TlCl, formed by a solid solution of TlI in TlCl, grows with a linear rate; the second, in contact with KI, formed by two solid solutions of TlCl in TlI and in KCl, respectively, grows according to the parabolic law. From marker experiments and X-ray analyses on product layer surfaces parallel to the original interface, along with a comparison of the rate constants and the diffusion coefficients, it was possible to deduce that the overall process is governed by diffusion of Tl⁺ and Cl^? in the iodide-rich solid solution Tl(I, Cl) and that the rate-determining step is the diffusion of Tl⁺.     

Cl+CH3OCl反应机理的理论研究

采用从头算方法,对多通道反应体系Cl+CH3OCl的反应机理进行了理论研究.在MP2/6-31+G(d,p)水平下优化了反应物、络合物、产物和过渡态的几何构型,并对得到的平衡几何构型进行了简谐振动频率分析.在相同水平下以过渡态为出发点,通过内禀反应坐标(IRC)理论计算了反应的最小能量路径.并且在MC-QCISD(T)/6-31G(d)高水平下进行了单点能量校正.研究结果表明,该反应存在4条可行的反应通道,其中生成HCl和CH2OCl的通道为主反应通道,其他反应通道为次反应通道.     

Kinetics of the reaction Cl + HO2 = HCl + O2, using molecular modulation spectrometry

The rate constant for the reaction (1), Cl + HO₂ → HCl + O₂, was measured using molecular modulation spectrometry to investigate HO₂ radical kinetics in the modulated photolysis of Cl₂? ;H₂? O₂ mixtures at 760 torr pressure. HO₂ was monitored directly in absorption at 220 nm, and k₁ was determined from computer simulations of the observed kinetic behavior of HO₂, using a simple chemical model. The results gave where k₄ is the rate constant for the reaction of Cl with H₂. A consensus value of k₄ gave k₁ = 6.9 × 10^?11 cm³/molecule sec, independent of temperature in the range of 274–338 K with an overall uncertainty of ±50%. The relative importance of reaction (1) for the conversion of Cl to HCl in the stratosphere is discussed briefly.     

Kinetics and catalysis by NaY entrapped Pt carbonyl clusters in the CO+NO reaction

[Pt₁₂(CO)₂₄]^2–/NaY and [Pt₉(CO)₁₈]^2–/NaY exhibited much higher activities in the CO+NO reaction at 473 K compared with Pt/Al₂O₃. Kinetic study andin-situ FTIR results suggest that NO adsorption is the rate-limiting step in the CO+NO reaction on intrazeolite Pt carbonyl clusters.     

Theoretical study of the mechanism of CH2CO + CN reaction

The potential energy surface information of the CH₂CO + CN reaction is obtained at the B3LYP/6‐311+G(d,p) level. To gain further mechanistic knowledge, higher‐level single‐point calculations for the stationary points are performed at the QCISD(T)/6‐311++G(d,p) level. The CH₂CO + CN reaction proceeds through four possible mechanisms: direct hydrogen abstraction, olefinic carbon addition–elimination, carbonyl carbon addition–elimination, and side oxygen addition–elimination. Our calculations demonstrate that R→IM1→TS3→P3: CH₂CN + CO is the energetically favorable channel; however, channel R→IM2→TS4→P4: CH₂NC + CO is considerably competitive, especially as the temperature increases (R, IM, TS, and P represent reactant, intermediate, transition state, and product, respectively). The present study may be helpful in probing the mechanism of the CH₂CO + CN reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

The global environment pollution includes pho-tochemical smog, acid rain and stratospheric ozonedepletion. The short-lived species/radicals in atmos-phere are closely related to these phenomena. Theshort-lived species/radicals bring the photochemicalsmog,…     

Multichannel RRKM study on the mechanism and kinetics of the CH3Cl + OH reaction

The kinetics and mechanism of the reaction of OH with CH₃Cl have been theoretically studied. The potential energy surface for each possible pathway has been investigated by the G2MP2 method. The rate constants for channels leading to several products have been calculated by multichannel‐Rice‐Ramsperger‐Kassel‐Marcus (RRKM) theory over a temperature range 200–2000 K. The results show the major channel is hydrogen abstraction mechanism. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Kinetics and mechanism of the chlorine dioxide-trithionate reaction

The trithionate-chlorine dioxide reaction has been studied spectrophotometrically in a slightly acidic medium at 25.0 ± 0.1 °C in acetate/acetic acid buffer monitoring the decay of chlorine dioxide at constant ionic strength (I = 0.5 M) adjusted by sodium perchlorate. We found that under our experimental conditions two limiting stoichiometries exist and the pH, the concentration of the reactants, and even the concentration of chloride ion affects the actual stoichiometry of the reaction that can be augmented by an appropriate linear combination of these limiting processes. It is also shown that although the formal kinetic order of trithionate is strictly one that of chlorine dioxide varies between 1 and 2, depending on the actual chlorine dioxide excess and the pH. Moreover, the otherwise sluggish chloride ion, which is also a product of the reaction, slightly accelerates the initial rate of chlorine dioxide consumption and may therefore act as an autocatalyst. In addition to that, overshoot-undershoot behavior is also observed in the [(·)ClO(2)]-time curves in the presence of chloride ion at chlorine dioxide excess. On the basis of the experiments, a 13-step kinetic model with 6 fitted kinetic parameter is proposed by nonlinear parameter estimation.     

The mechanism of the OH + CO reaction and the stability of the HOCO radical

The mechanism of the reaction between OH radicals and CO is discussed in relation to recent experiments which indicate that the rate constant, k = ?(dln[OH]/dt)/[CO], depends on total pressure. It is shown that this observation is quite consistent with the known spectroscopic and thermodynamic properties of the HOCO radical, as long as the dissociation of HOCO to H + CO₂ is no faster than that to OH + CO.     

Kinetics and mechanism of the NCN + NO2 reaction studied by experiment and theory

The rate constant for the NCN + NO 2 reaction has been measured by a laser photolysis/laser-induced fluorescence technique in the temperature range of 260-296 K at pressures between 100 and 500 Torr with He and N 2 as buffer gases. The NCN radical was produced from the photolysis of NCN 3 at 193 nm and monitored by laser-induced fluorescence with a dye laser at 329.01 nm. The rate constant was found to increase with pressure but decrease with temperature, indicating that the reaction occurs via a long-lived intermediate stabilized by collisions with buffer gas. The reaction mechanism and rate constant are also theoretically predicted for the temperature range of 200-2000 K and the He and N 2 pressure range of 10 (-4) Torr to 1000 atm based on dual-channel Rice-Ramsperger-Kassel-Marcus (RRKM) theory with the potential energy surface evaluated at the G2M//B3LYP/6-311+G(d) level. In the low-temperature range (<700 K), the most favorable reaction is the barrierless association channel that leads to the intermediate complex (NCN-NO 2). At high temperature, the direct O-abstraction reaction with a barrier of 9.8 kcal/mol becomes the dominant channel. The rate constant calculated by RRKM theory agrees reasonably well with experimental data.     

Investigation on the mechanism and applications of the reaction Cl2+2HBr=2HCl+Br2

The mechanism of reaction Cl₂+2HBr=2HCl+Br₂ has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G^** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions Cl₂+HBr→HCl+BrCl and BrCl+HBr→HCl+Br₂ is smaller than the dissociation energy of Cl₂, HBr and BrCl, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br₂ from HBr. Gaseous Cl₂ directly reacts with HBr gas, which produces gaseous mixtures containing Br₂, and liquid Br₂ and HCl are obtained by cooling the mixtures and further separated by absorption with CCl₄. The recovery percentage of Br₂ is more than 96%, and the Cl₂ remaining in liquid Br₂ is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.