Kinetics of Cl(2P) reactions with CF3CHCl2, CF3CHFCl,and CH3CFCl2

The rate coefficients for the removal of Cl atoms by reaction with three HCFCs, CF₃CHCl₂ (HCFC-123), CF₃CHFCl (HCFC-124), and CH₃CFCl₂ (HCFC 141b), were measured as a function of temperature between 276 and 397 K. CH₃CF₂Cl (HCFC-142b) was studied only at 298 K. The Arrhenius expressions obtained are: k₁ = (3.94 ± 0.84)× 10^?12 exp[?(1740 ± 100)/T] cm³ molecule^?1 s^?1 for CF₃CHCl₂ (HCFC 123); k₂ = (1.16 ± 0.41) × 10^?12 exp[?(1800 ± 150)/T] cm³ molecule^?1 s^?1 for CF₃CHFCl (HCFC 124); and k₃ = (1.6 ± 1.1) × 10^?12 exp[?(1800 ± 500)/T] cm³ molecule^?1 s^?1 for CH₃CFCl₂ (HCFC 141b). In case of HCFC 141b, non-Arrhenius behavior was observed at temperatures above ca. 350 K and is attributed to the thermal decomposition of CH₂CFCl₂ product into Cl + CH₂CFCl. In case of HCFC-142b, only an upper limit for the 298 K value of the rate coefficient was obtained. The atmospheric significance of these results are discussed. © 1993 John Wiley & Sons, Inc.     

Kinetics of the reactions of Cl atoms with CH3Br and CH2Br2

The rate coefficients for the reactions of Cl atoms with CH₃Br, (k₁) and CH₂Br₂, (k₂) were measured as functions of temperature by generating Cl atoms via 308 nm laser photolysis of Cl₂ and measuring their temporal profiles via resonance fluorescence detection. The measured rate coefficients were: k₁ = (1.55 ± 0.18) × 10^?11 exp{(?1070 ± 50)/T} and k₂ = (6.37 ± 0.55) × 10^?12 exp{(?810 ± 50)/T} cm³ molecule^?1 s^?1. The possible interference of the reaction of CH₂Br product with Cl₂ in the measurement of k₁ was assessed from the temporal profiles of Cl at high concentrations of Cl₂ at 298 K. The rate coefficient at 298 K for the CH₂Br + Cl₂ reaction was derived to be (5.36 ± 0.56) × 10^?13 cm³ molecule^?1 s^?1. Based on the values of k₁ and k₂, it is deduced that global atmospheric lifetimes for CH₃Br and CH₂Br₂ are unlikely to be affected by loss via reaction with Cl atoms. In the marine boundary layer, the loss via reaction (1) may be significant if the Cl concentrations are high. If found to be true, the contribution from oceans to the overall CH₃Br budget may be less than what is currently assumed. © 1994 John Wiley & Sons, Inc.     

Kinetics of fluorine atom reactions using resonance absorption spectrometry in the far vacuum ultraviolet reactions F + HCl,CH4, CHCl3 CHCl2F,and CHClF2

Atomic resonance absorption spectrometry with a nonreversed fluorine resonance lamp (～95 nm) has been used to study the kinetics of elementary reactions of ground state F²P_J atoms in a discharge-flow system. The following rate constants (in cm³/molec·sec)

1 All rate constants are given with 1.5 σ.

were determined at 298° K: The reaction F ₂P_J + HCl(1) was found to give J-excited Cl ₂P_1/2 atoms with a product branching ratio [Cl ₂P_1/2]/[Cl ₂P_3/2] = 0.10.     

Direct dynamics study of the hydrogen abstraction reaction of CF3CH2Cl + Cl → CF3CHCl + HCl

The hydrogen abstraction reaction of Cl atoms with CF₃CH₂Cl (HCFC‐133a) is investigated by using density function theory and ab initio approach, and the rate constants are calculated by using the dual‐level direct dynamics method. Optimized geometries and frequencies of reactants, transition state, and products are computed at the B3LYP/6‐311+G(2d,2p) level. To refine the energetic information along the minimum energy path, single‐point energy calculations are carried out at the G3(MP2) level of theory. The interpolated single‐point energy method is employed to correct the energy profiles for the title reaction. The rate constants are evaluated by using the canonical variational transition state theory with a small‐curvature tunneling correction over a wide range of temperature, 200–2000 K. The variational effect for the reaction is moderate at low temperatures and very small at high temperatures. However, the tunneling correction has an important contribution in the lower temperature range. The agreement between calculated rate constants and available experimental values is good at lower temperatures but diverges significantly at higher temperatures. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 661–667, 2012     

CH3OCF2CF2OCH3+Cl的反应机理及动力学性质

利用密度泛函理论直接动力学方法研究了反应CH₃OCF₂CF₂OCH₃+Cl的微观机理和动力学性质. 在BB1K/6-31+G(d,p)水平上获得了反应的势能面信息, 计算中考虑了反应物CH₃OCF₂CF₂OCH₃两个稳定构象(SC1和SC2)的氢提取通道和取代反应通道. 利用改进的正则变分过渡态理论结合小曲率隧道效应(ICVT/SCT)计算了各氢提取通道的速率常数, 进而根据Boltzmann配分函数得到总包反应速率常数(k_T)以及每个构象对总反应的贡献. 结果表明296 K温度下计算的k_T(ICVT/SCT)值与已有实验值符合得很好. 由于缺乏其他温度速率常数的实验数据, 我们预测了该反应在200-2000 K温度区间内反应速率常数的三参数表达式: k_T=0.40×10^-14T^1.05exp(-206.16/T).     

Kinetics of the reactions of CH3O with Cl and CIO

The kinetics of the reactions CH₃O + Cl → H₂CO + HCl (1) and CH₃O + ClO → H₂CO + HOCl (2) have been studied using the discharge-flow techniques. CH₃O was monitored by laser-induced fluorescence, whereas mass spectrometry was used for the detection or titration of other species. The rate constants obtained at 298 K are: k₁ = (1.9 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂ = (2.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. These data are useful to interpret the results of the studies of the reactions of CH₃O₂ with Cl and ClO which, at least partly, produce CH₃O radicals. © 1996 John Wiley & Sons, Inc.     

Rate constants and hydrogen isotope substitution effects in the CH3 + HCl and CH3 + Cl2 reactions

The kinetics of the CH3 + Cl2 (k2a) and CD3 + Cl2 (k2b) reactions were studied over the temperature range 188-500 K using laser photolysis-photoionization mass spectrometry. The rate constants of these reactions are independent of the bath gas pressure within the experimental range, 0.6-5.1 Torr (He). The rate constants were fitted by the modified Arrhenius expression, k2a = 1.7 x 10(-13)(T/300 K)(2.52)exp(5520 J mol(-1)/RT) and k2b = 2.9 x 10(-13)(T/300 K)(1.84)exp(4770 J mol(-1)/RT) cm(3) molecule(-1) s(-1). The results for reaction 2a are in good agreement with the previous determinations performed at and above ambient temperature. Rate constants of the CH3 + Cl2 and CD3 + Cl2 reactions obtained in this work exhibit minima at about 270-300 K. The rate constants have positive temperature dependences above the minima, and negative below. Deuterium substitution increases the rate constant, in particular at low temperatures, where the effect reaches ca. 45% at 188 K. These observations are quantitatively rationalized in terms of stationary points on a potential energy surface based on QCISD/6-311G(d,p) geometries and frequencies, combined with CCSD(T) energies extrapolated to the complete basis set limit. 1D tunneling as well as the possibility of the negative energies of the transition state are incorporated into a transition state theory analysis, an approach which also accounts for prior experiments on the CH3 + HCl system and its various deuterated isotopic substitutions [Eskola, A. J.; Seetula, J. A.; Timonen, R. S. Chem. Phys. 2006, 331, 26].     

Kinetics of the reactions of chlorinated methyl radicals (CH2Cl, CHCl2, and CCl3) with NO2 in the temperature range 220-360 K

The kinetics of the reactions of chlorinated methyl radicals (CH2Cl, CHCl2, and CCl3) with NO2 have been studied in direct measurements at temperatures between 220 and 360 K using a tubular flow reactor coupled to a photoionization mass spectrometer. The radicals have been homogeneously generated at 193 or 248 nm by pulsed laser photolysis of appropriate precursors. Decays of radical concentrations have been monitored in time-resolved measurements to obtain the reaction rate coefficients under pseudo-first-order conditions with the amount of NO2 being in large excess over radical concentrations. The bimolecular rate coefficients of all three reactions are independent of the bath gas (He or N2) and pressure within the experimental range (1-6 Torr) and are found to depend on temperature as follows: k(CH2Cl + NO2) = (2.16 +/- 0.08) x 10(-11) (T/300 K)(-1.12+/-0.24) cm3 molecule(-1) s(-1) (220-363 K), k(CHCl2 + NO2) = (8.90 +/- 0.16) x 10(-12) (T/300 K)(-1.48+/-0.13) cm3 molecule(-1) s(-1) (220-363 K), and k(CCl3 + NO2) = (3.35 +/- 0.10) x 10(-12) (T/300 K)(-2.2+/-0.4) cm3 molecule(-1) s(-1) (298-363 K), with the uncertainties given as one-standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are about +/-25%. In the reactions CH2Cl + NO2, CHCl2 + NO2, and CCl3 + NO2, the products observed are formaldehyde, CHClO, and phosgene (CCl2O), respectively. In addition, a weak signal for the HCl formation has been detected for the CHCl2 + NO2 reaction.     

Hydrochlorination of unsaturated compounds by the action of CH2Cl2 or CHCl3 and rhodium complexes

A new method has been developed for the catalytic hydrochlorination of olefins and acetylenes in the presence of Rh complexes by means of HCl generated in situ from CH₂Cl₂ and CHCl₃ under the reaction conditions. The reaction was studied using the hydrochlorination of propylene, 1-hexene, 1-nonene, vinyl-cyclopropane, 1,1-dicyclopropylethylene, cyclohexene, cyclooctene, norbornene, and 1,5-cyclooctadiene as examples.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1373–1377, June, 1991.     

Deactivation of I(2P1/2) by CH3Cl,CH2Cl2, CHCl3, CCl3F,and CCl4

Collisional deactivation of I(²P_1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH₃Cl, CH₂Cl₂, CHCl₃, CCl₃F, and CCl₄ are 3.1±0.3×10⁻¹³, 1.28±0.08×10⁻¹³, 5.7±0.3×10⁻¹⁴, 3.9±0.4×10⁻¹⁵, and 2.3±0.3×10⁻¹⁵cm³ molecule⁻¹ s⁻¹, respectively, at room temperature (298 K). The higher efficiency observed for relaxation by CH₃Cl, CH₂Cl₂, and CHCl₃ reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm⁻¹) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799–803, 1998     

Anion-controlled redistribution reactions in the system C3Cl3+A−/(CH3)3SiN(CH3)2

Transmination reactions of the 4z-exchange type between C₃Cl₃⁺A^? and (CH₃)₃SiN(CH₃)₂ are introduced as a novel mode of aromatic substitution at the C₃⁺-core. The extent of transamination can be controlled by appropriate choice of counterion A^?.     

Kinetics of the reactions of chlorine atoms with CH3ONO and CH3ONO2

The kinetics of the reactions of Cl atoms with CH₃ONO and CH₃ONO₂ have been studied using relative rate techniques. In 700 Torr of nitrogen diluent at 295 ± 2K, k(Cl + CH₃ONO) = (2.1 ± 0.2) × 10⁻¹² and k(Cl + CH₃ONO₂) = (2.4 ± 0.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The result for k(Cl + CH₃ONO₂) is in good agreement with the literature data. The result for k(Cl + CH₃ONO) is a factor of 4.5 lower than that reported previously. It seems likely that in the previous study most of the loss of CH₃ONO which was attributed to reaction with Cl atoms was actually caused by photolysis leading to an overestimate of k(Cl + CH₃ONO). © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 357–359, 1999     

Oxidative pyrolysis of CH2Cl2, CHCl3, and CCl4-I: Incineration implications

The oxidative pyrolysis of methylene chloride, chloroform, and carbon tetrachloride has been investigated using a micro-bore, fused silica, tubular flow reactor operating under laminar flow conditions coupled to in-line GC-MS detection. Data were obtained over the temperature range 573–1273 K for the following conditions: chlorocarbon/oxygen equivalence ratios of 3.0, chlorocarbon concentrations of 2.7 ± 0.1 × 10^?5 mols/L, gas-phase residence times of 2.0 s, and reactor pressures of 1.15 ± 0.05 atm. The parent stability (defined by the temperature required for 99% destruction) was evaluated as: Chemically activated recombination of chlorinated C₁ radicals are proposed as important pathways to chlorinated ethane and olefin products. The most significant finding from analysis of product distributions containing ≥2 carbon atoms was the observation of ca. 1 mol% yields of higher-molecular-weight perchlorinated aromatic species from the decomposition of chloroform and carbon tetrachloride. Implications with respect to the controlled high-temperature incineration of these chlorinated methanes are briefly discussed.     

Laser photolysis/laser-induced fluorescence studies of reaction rates of OH with CH3Cl,CH2Cl2, and CHCl3 over an extended temperature range

A modified laser photolysis/laser-induced fluorescence technique has been used to measure atmospheric pressure absolute rate coefficients for the reaction of hydroxyl (OH) radicals with the chlorinated methanes (CH₃Cl, CH₂Cl₂, and CHCl₃). Data have been obtained for these compounds over the widest temperature range (292–800 K) that has been reported in the literature using a single experimental apparatus. The temperature dependence of the rate data is best represented by the following three-parameter expressions: Uncertainties in the pre-exponential and exponential term are expressed as 95% confidence intervals. For the temperature exponent, error limits represent a ±10% change in the total error of best fit. The degree of curvature in the Arrhenius plots appeared to increase with increasing Cl substitution of the reactant. However, the uncertainty in the temperature exponent for the CH₃Cl data was large in comparison with the other chlorinated methanes. Thus, data of greater precision at elevated temperatures are necessary to further explore this relationship. The rate coefficients were compared with recent semiempirical and transition state theory models for haloalkane-OH hydrogen transfer reactions over a temperature range of 250–800 K. The transition state model of Cohen and Benson was in excellent agreement with the CH₃Cl and CH₂Cl₂ data. The semiempirical structure activity relationship developed by Atkinson represented the best fit of the CHCl₃ data, although it underestimated the experimental data by more than a factor of 2 at 800 K. The extreme care used to remove and alayze for reactive impurities along with the agreement with other experimental studies suggests that transition state and semi-empirical models for CHCl₃ must be modified to account its reaction behavior at high temperature.     

An FTIR study of the Cl atom-initiated oxidation of CH2Cl2 and CH3Cl

The Cl atom-initiated oxidation of CH₂Cl₂ and CH₃Cl was studied using the FTIR method in the photolysis of mixtures typically containing Cl₂ and the chlorinated methanes at 1 torr each in 700 torr air. The results obtained from product analysis were in general agreement with those reported by Sanhueza and Heicklen. The relative rate constant for the Cl atom reactions of CH₂Cl₂ and CH₃Cl was determined to be k(Cl +CH₃Cl)/k(Cl + CH₂Cl₂) = 1.31 ± 0.14 (2σ) at 298 ± 2 K.     

Theoretical study of the reactions CF3CH2OCHF2 + OH/Cl and its product radicals and parent ether(CH3CH2OCH3) with OH

A dual-level direct dynamic method is employed to study the reaction mechanisms of CF3CH2OCHF2 (HFE-245fa2; HFE-245mf) with the OH radicals and Cl atoms. Two hydrogen abstraction channels and two displacement processes are found for each reaction. For further study, the reaction mechanisms of its products (CF3CH2OCF2 and CF3CHOCHF2) and parent ether CH3CH2OCH3 with OH radical are investigated theoretically. The geometries and frequencies of all the stationary points and the minimum energy paths (MEPs) are calculated at the B3LYP/6-311G(d,p) level. The energetic information along the MEPs is further refined at the G3(MP2) level of theory. For reactions CF3CH2OCHF2 + OH/Cl, the calculation indicates that the hydrogen abstraction from --CH2-- group is the dominant reaction channel, and the displacement processes may be negligible because of the high barriers. The standard enthalpies of formation for the reactant CF3CH2OCHF2, and two products CF3CH2OCHF2 and CF3CHOCHF2 are evaluated via group-balanced isodesmic reactions. The rate constants of reactions CF3CH2OCHF2 + OH/Cl and CH3CH2OCH3 + OH are estimated by using the variational transition state theory over a wide range of temperature (200-2000 K). The agreement between the theoretical and experimental rate constants is good in the measured temperature range. From the comparison between the rate constants of the reactions CF3CH2OCHF2 and CH3CH2OCH3 with OH, it is shown that the fluorine substitution decreases the reactivity of the C--H bond.     

State-to-state dynamics of the Cl + CH3OH --> HCl + CH2OH reaction

Molecular chlorine, methanol, and helium are co-expanded into a vacuum chamber using a custom designed "late-mixing" nozzle. The title reaction is initiated by photolysis of Cl2 at 355 nm, which generates monoenergetic Cl atoms that react with CH3OH at a collision energy of 1960 +/- 170 cm(-1) (0.24 +/- 0.02 eV). Rovibrational state distributions of the nascent HCl products are obtained via 2 + 1 resonance enhanced multiphoton ionization, center-of-mass scattering distributions are measured by the core-extraction technique, and the average internal energy of the CH3OH co-products is deduced by measuring the spatial anisotropy of the HCl products. The majority (84 +/- 7%) of the HCl reaction products are formed in HCl(v = 0) with an average rotational energy of [Erot] = 390 +/- 70 cm(-1). The remaining 16 +/- 7% are formed in HCl(v = 1) and have an average rotational energy of [Erot] = 190 +/- 30 cm(-1). The HCl(v = 1) products are primarily forward scattered, and they are formed in coincidence with CH2OH products that have little internal energy. In contrast, the HCl(v = 0) products are formed in coincidence with CH2OH products that have significant internal energy. These results indicate that two or more different mechanisms are responsible for the dynamics in the Cl + CH3OH reaction. We suggest that (1) the HCl(v = 1) products are formed primarily from collisions at high impact parameter via a stripping mechanism in which the CH2OH co-products act as spectators, and (2) the HCl(v = 0) products are formed from collisions over a wide range of impact parameters, resulting in both a stripping mechanism and a rebound mechanism in which the CH2OH co-products are active participants. In all cases, the reaction of fast Cl atoms with CH3OH is with the hydrogen atoms on the methyl group, not the hydrogen on the hydroxyl group.     

CH3 + Cl = CH3Cl: RRKM/master equation modeling

Data for the title reaction have been fitted using an RRKM/master equation approach. Energy transfer was modeled using an exponential decay with downward step sizes, ΔE_d, as a fitting parameter. The low temperature (200 < T (K) < 300) combination of CH₃ with Cl atoms in He can be accommodated with ΔE_d (cm^?1) = 400. Higher temperature (1600 < T (K) < 2100) decomposition in Ar required ΔE_d(T) (cm^?1) = 694(T/300)^0.46. Previous analysis of the analogous system CH₄ = CH₃ + H required ΔE_d(T) (cm^?1) = 100(T/300) for He and ΔE_d(T) (cm^?1) = 150(T/300) for Ar. Understanding of the magnitudes and temperature dependence of ΔE_d remains the greatest detriment to quantitative calculation, extrapolation, and prediction of unimolecular rate constants. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 245–254, 2009     

Imaging photon-initiated reactions: a study of the Cl(2P(3/2))+CH4-->HCl+CH3 reaction

The hydrogen or deuterium atom abstraction reactions between Cl((2)P(3/2)) and methane, or its deuterated analogues CD(4) and CH(2)D(2), have been studied at mean collision energies around 0.34 eV. The experiments were performed in a coexpansion of molecular chlorine and methane in helium, with the atomic Cl reactants generated by polarized laser photodissociation of Cl(2) at 308 nm. The Cl-atom reactants and the methyl radical products were detected using (2+1) resonantly enhanced multiphoton ionization, coupled with velocity-map ion imaging. Analysis of the ion images reveals that in single-beam experiments of this type, careful consideration must be given to the spread of reagent velocities and collision energies. Using the reactions of Cl with CH(4), CD(4), and CH(2)D(2), as examples, it is shown that the data can be fitted well if the reagent motion is correctly described, and the angular scattering distributions can be obtained with confidence. New evidence is also provided that the CD(3) radicals from the Cl+CD(4) reaction possess significant rotational alignment under the conditions of the present study. The results are compared with previous experimental and theoretical works, where these are available.