Kinetic and thermochemical parameters of chlorine atom transfer reactions from CF3Cl,CF3CF2Cl,CF2ClCF2Cl,and CF2ClCFCl2 in gas phase

The following reactions: (1) were studied over the temperature ranges 533–687 K, 563–663 K, and 503–613 K for the forward reactions respectively and over 683–763 K, for the back reaction. Arrhenius parameters for chlorine atom transfer were determined relative to the combination of the attacking radicals. The ΔH_r°(1) = ?3.95 ± 0.45 kcal mol^?1 was calculated and from this value the ΔH∮(C₂F₅Cl) = ?2.66.3 ± 2.5 kcal mol^?1 and D(C₂F₅-Cl) = 82.0 ± 1.2 kcal mol^?1 were obtained. Besides, the ΔH_r°(2) was estimated leading to D(CF₂ClCF₂Cl) = 79.2 ± 5 Kcal mol^?1. The bond dissociation energies and the heat of formation are compared with those of the literature. The effect of the halogen substitutents as well as the importance of the polar effects for halogen transfer processes are discussed.     

Kinetic mechanism of the hydrogen abstraction reactions of the chlorine atoms with CH3CF2Cl and CH3CFCl2: a dual level direct dynamics study

The mechanisms of the reactions: CH(3)CFCl(2) + Cl (R1) and CH(3)CF(2)Cl + Cl (R2) are studied over a wide temperature range (200-3000 K) using the dual-level direct dynamics method. The minimum energy path calculation is carried out at the MP2/6-311G(d,p) and B3LYP/6-311G(d,p) levels, and energetic information is further refined by the G3(MP2) theory. The H-abstraction from the out-of-plane for (R1) is the major reaction channel, while the in-plane H-abstraction is the predominant route of (R2). The canonical variational transition-state theory (CVT) with the small-curvature tunneling (SCT) correction method is used to calculate the rate constants. Using group-balanced isodesmic reactions and hydrogenation reactions as working chemical reactions, the standard enthalpies of formation for CH(3)CFCl(2), CH(3)CF(2)Cl, CH(2)CFCl(2), and CH(2)CF(2)Cl are evaluated at the CCSD(T)/6-311 + G(3df,2p)//MP2/6-311G(d,p) level of theory. The results indicate that the substitution of fluorine atom for the chlorine atom leads to a decrease in the C-H bond reactivity with a small increase in reaction enthalpies. Also, for all reaction pathways the variational effect is small and the SCT effect is only important in the lower temperature range on the rate constants.     

Kinetics of the reactions of halogenated methyl radicals (CF3, CF2Cl,CFCl2, and CCl3) with molecular chlorine

The kinetics of four gas-phase reactions involving halogenated methyl radicals (R ? CF₃, CF₂Cl, CFCI₂, and CCI₃) with molecular chlorine have been studied using a tubular reactor coupled to a photoionization mass spectrometer. The radicals were homogeneously generated by the pulsed photolysis of precursor molecules at 193 nm. The subsequent decays of the radical concentration were monitored in real-time experiments as a function of Cl₂ concentration to obtain the rate constants of these R + Cl₂ reactions. Where possible, the rate constants were measured as a function of temperature to determine Arrhenius parameters. Apparent discrepancies between these measured rate constants for CF₃ and CCl₃ with Cl₂ and ones obtained in prior indirect studies are explained. The higher activation energies for these R + Cl₂ reactions compared to that of the CH₃ + Cl₂ reaction are attributed in part to the different polarities of the transition states formed.     

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.     

Kinetic study of the reactions of Cl atoms with CF3CH2CH2OH, CF3CF2CH2OH, CHF2CF2CH2OH, and CF3CHFCF2CH2OH

The reaction kinetics of chlorine atoms with a series of partially fluorinated straight-chain alcohols, CF(3)CH(2)CH(2)OH (1), CF(3)CF(2)CH(2)OH (2), CHF(2)CF(2)CH(2)OH (3), and CF(3)CHFCF(2)CH(2)OH (4), were studied in the gas phase over the temperature range of 273-363 K by using very low-pressure reactor mass spectrometry. The absolute rate coefficients were given by the expressions (in cm(3) molecule(-1) s(-1)): k(1) = (4.42 +/- 0.48) x 10(-11) exp(-255 +/- 20/T); k(1)(303) = (1.90 +/- 0.17) x 10(-11), k(2) = (2.23 +/- 0.31) x 10(-11) exp(-1065 +/- 106/ T); k(2)(303) = (6.78 +/- 0.63) x 10(-13), k(3) = (8.51 +/- 0.62) x 10(-12) exp(-681 +/- 72/T); k(3)(303) = (9.00 +/- 0.82) x 10(-13) and k(4) = (6.18 +/- 0.84) x 10(-12) exp(-736 +/- 42/T); k(4)(303) = (5.36 +/- 0.51) x 10(-13). The quoted 2sigma uncertainties include the systematic errors. All title reactions proceed via a hydrogen atom metathesis mechanism leading to HCl. Moreover, the oxidation of the primarily produced radicals was investigated, and the end products were the corresponding aldehydes (R(F)-CHO; R(F) = -CH(2)CF(3), -CF(2)CF(3), -CF(2)CHF(2), and -CF(2)CHFCF(3)), providing a strong experimental indication that the primary reactions proceed mainly via the abstraction of a methylenic hydrogen adjacent to a hydroxyl group. Finally, the bond strengths and ionization potentials for the title compounds were determined by density functional theory calculations, which also suggest that the alpha-methylenic hydrogen is mainly under abstraction by Cl atoms. The correlation of room-temperature rate coefficients with ionization potentials for a set of 27 molecules, comprising fluorinated C2-C5 ethers and C2-C4 alcohols, is good with an average deviation of a factor of 2, and is given by the expression log(k) (in cm(3) molecule(-1) s(-1)) = (5.8 +/- 1.4) - (1.56 +/- 0.13) x (ionization potential (in eV)).     

Kinetic study of the reaction of chlorine atoms with CF3I and the reactions of CF3 radicals with O2, Cl2 and NO at 296 K

The kinetics of the gas-phase reaction of Cl atoms with CF₃I have been studied relative to the reaction of Cl atoms with CH₄ over the temperature range 271–363 K. Using k(Cl + CH₄) = 9.6 × 10^?12 exp(?2680/RT) cm³ molecule^?1 s^?1, we derive k(Cl + CF₃I) = 6.25 × 10^?11 exp(?2970/RT) in which E_a has units of cal mol^?1. CF₃ radicals are produced from the reaction of Cl with CF₃I in a yield which was indistinguishable from 100%. Other relative rate constant ratios measured at 296 K during these experiments were k(Cl + C₂F₅I)/k(Cl + CF₃I) = 11.0 ± 0.6 and k(Cl + C₂F₅I)/k(Cl + C₂H₅Cl) = 0.49 ± 0.02. The reaction of CF₃ radicals with Cl₂ was studied relative to that with O₂ at pressures from 4 to 700 torr of N₂ diluent. By using the published absolute rate constants for k(CF₃ + O₂) at 1–10 torr to calibrate the pressure dependence of these relative rate constants, values of the low- and high-pressure limiting rate constants have been determined at 296 K using a Troe expression: k₀(CF₃ + O₂) = (4.8 ± 1.2) × 10^?29 cm⁶ molecule^?2 s^?1; k_∞(CF₃ + O₂) = (3.95 ± 0.25) × 10^?12 cm³ molecule^?1 s^?1; F_c = 0.46. The value of the rate constant k(CF₃ + Cl₂) was determined to be (3.5 ± 0.4) × 10^?14 cm³ molecule^?1 s^?1 at 296 K. The reaction of Cl atoms with CF₃I is a convenient way to prepare CF₃ radicals for laboratory study. © 1995 John Wiley & Sons, Inc.     

The CO_2 laser-induced radical-chain reactions between CH_3CF_2H and chlorine-atom donors CF_2ClCFCl_2, CF_3CCl_3 CFCl_3 or CF_2Cl_2

The CO_2 laser induced room temperature reactions of CH_3CF_2H or another protium-donorCH_3CHClCH_3 with chlorine-atom donors (Z--Cl) CFCl_2CF_2Cl, CF_3CCl_3, CFCl_3 or CF_2Cl_2, havebeen investigated. Some of these reactions can yield two important monomers (CF_2=CH_2 andCF_2=CFCl) for fluoropolymers simultaneously. The yield dependence of these two alkenes on experi-mental conditions has been studied. A laser-initiated chain process is supported by identifica-tion of Z--H intermediates in these reactions.     

Atmospheric chemistry of CF3CH=CH2 and C4F9CH=CH2: products of the gas-phase reactions with Cl atoms and OH radicals

FTIR-smog chamber techniques were used to study the products of the Cl atom and OH radical initiated oxidation of CF3CH=CH2 in 700 Torr of N2/O2, diluent at 296 K. The Cl atom initiated oxidation of CF3CH=CH2 in 700 Torr of air in the absence of NOx gives CF3C(O)CH2Cl and CF3CHO in yields of 70+/-5% and 6.2+/-0.5%, respectively. Reaction with Cl atoms proceeds via addition to the >C=C< double bond (74+/-4% to the terminal and 26+/-4% to the central carbon atom) and leads to the formation of CF3CH(O)CH2Cl and CF3CHClCH2O radicals. Reaction with O2 and decomposition via C-C bond scission are competing loss mechanisms for CF3CH(O)CH2Cl radicals, kO2/kdiss=(3.8+/-1.8)x10(-18) cm3 molecule-1. The atmospheric fate of CF3CHClCH2O radicals is reaction with O2 to give CF3CHClCHO. The OH radical initiated oxidation of CxF2x+1CH=CH2 (x=1 and 4) in 700 Torr of air in the presence of NOx gives CxF2x+1CHO in a yield of 88+/-9%. Reaction with OH radicals proceeds via addition to the >C=C< double bond leading to the formation of CxF2x+1C(O)HCH2OH and CxF2x+1CHOHCH2O radicals. Decomposition via C-C bond scission is the sole fate of CxF2x+1CH(O)CH2OH and CxF2x+1CH(OH)CH2O radicals. As part of this work a rate constant of k(Cl+CF3C(O)CH2Cl)=(5.63+/-0.66)x10(-14) cm3 molecule-1 s-1 was determined. The results are discussed with respect to previous literature data and the possibility that the atmospheric oxidation of CxF2x+1CH=CH2 contributes to the observed burden of perfluorocarboxylic acids, CxF2x+1COOH, in remote locations.     

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.     

Rate constants for the reactions of OH radicals with CH3OCF2CF3, CH3OCF2CF2CF3, and CH3OCF(CF3)2

The rate constants for the reactions of OH radicals with CH₃OCF₂CF₃, CH₃OCF₂CF₂CF₃, and CH₃OCF(CF₃)₂ have been measured over the temperature range 250–430 K. Kinetic measurements have been carried out using the flash photolysis, laser photolysis, and discharge flow methods combined respectively with the laser induced fluorescence technique. The influence of impurities in the samples was investigated by using gas‐chromatography. The following Arrhenius expressions were determined: k(CH₃OCF₂CF₃) = (1.90) × 10⁻¹² exp[−(1510 ± 120)/T], k(CH₃OCF₂CF₂CF₃) = (2.06) × 10⁻¹² exp[−(1540 ± 80)/T], and k(CH₃OCF(CF₃)₂) = (1.94) × 10⁻¹² exp[−(1450 ± 70)/T] cm³ molecule⁻¹ s⁻¹. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 846–853, 1999     

On the kinetic mechanism of the hydrogen abstraction reactions of the hydroxyl radical with CH3CF2Cl and CH3CFCl2: A dual level direct dynamics study

By means of the dual‐level direct dynamics method, the mechanisms of the reactions, CH₃CF₂Cl + OH → products (R1) and CH₃CFCl₂ + OH → products (R2), are studied over a wide temperature range 200–2000 K. The optimized geometries and frequencies of the stationary points are calculated at the MP2/6‐311G(d,p) level, and then the energy profiles of the reactions are refined with the interpolated single‐point energy method at the G3(MP2) level. The canonical variational transition‐state theory with the small‐curvature tunneling (SCT) correction method is used to calculate the rate constants. For the title reactions, three reaction channels are identified and the H‐abstraction channel is the major pathway. The results indicate that F substitution has a significant (reductive) effect on hydrochlorofluorocarbon reactivity. Also, for all H‐abstraction reaction channels the variational effect is small and the SCT effect is only important in the lower temperature range on the rate constants calculation. © 2009 Wiley Periodicals, Inc. J Comput Chem, 2010     

用交叉分子束研究O(^3p)与CF2=CFCl,CF2=CFBr,CF2=CH2的反应

本文报道在交叉分子束装置中, 研究氧原子和CF2=CFCl, CF2=CFBr,CF2=CH2的反应。在O(^3p)和CF2=CFBr(或CF2=CFBr)反应中, 首次观察到反应生成的CF2(^3B1)的发射光谱, 而在O与CF2=CH2反应中, 用激光诱导荧光方法检测到CFH卡宾, 确定了在此反应中CFH卡宾的生成, 这一结果未见文献报道。并根据这些结果, 分析和讨论了在这些反应中, 生成CF2(^3B1)和CHF卡宾的机理。     

Theoretical studies of the reactions of CF3CHCLOCHF2/CF3CHFOCHF2 with OH radical and Cl atom and their product radicals with OH

The mechanisms and dynamics studies of the OH radical and Cl atom with CF(3)CHClOCHF(2) and CF(3)CHFOCHF(2) have been carried out theoretically. The geometries and frequencies of all the stationary points are optimized at the B3LYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the G3(MP2) level of theory. For each reaction, two H-abstraction channels are found and four products (CF(3)CHFOCF(2), CF(3)CFOCHF(2), and CF(3)CHClOCF(2), CF(3)CClOCHF(2)) are produced during the above processes. The rate constants for the CF(3)CHClOCHF(2)/CF(3)CHFOCHF(2) + OH/Cl reactions are calculated by canonical variational transition-state theory (CVT) within 200-2000 K, and the small-curvature tunneling is included. The total rate constants calculated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental data. The Arrhenius expressions for the reactions are obtained. Our calculation shows that the substitution of Cl by F decreases the reactivity of CF(3)CHClOCHF(2) toward OH and Cl. In addition, the mechanisms of subsequent reactions of product radicals and OH radical are further investigated at the G3(MP2)//B3LYP/6-311G(d,p) level, and the main products are predicted in the this article.     

Theoretical study of H-abstraction reactions from CH3Cl and CH3Br molecules by ClO and BrO radicals

The rate constants of the H-abstraction reactions from CH(3)Cl and CH(3)Br molecules by ClO and BrO radicals have been estimated over the temperature range of 300-2500 K using four different levels of theory. Calculations of optimized geometrical parameters and vibrational frequencies are performed using B3LYP and MP2 methods combined with the cc-pVTZ basis set. Single-point energy calculations have been carried out with the highly correlated ab initio coupled cluster method in the space of single, double, and triple (perturbatively) electron excitations CCSD(T) using the cc-pVTZ and cc-pVQZ basis sets. Canonical transition-state theory combined with an Eckart tunneling correction has been used to predict the rate constants as a function of temperature. In order to choose the appropriate levels of theory with chlorine- and bromine-containing species, the reference reaction Cl ((2)P(3/2)) + CH(3)Cl → HCl + CH(2)Cl (R(ref)) was first theoretically studied because its kinetic parameters are well-established from numerous experiments, evaluation data, and theoretical studies. The kinetic parameters of the reaction R(ref) have been determined accurately using the CCSD(T)/cc-pVQZ//MP2/cc-pVTZ level of theory. This level of theory has been used for the rate constant estimation of the reactions ClO + CH(3)Cl (R(1)), ClO + CH(3)Br (R(2)), BrO + CH(3)Cl (R(3)), and BrO + CH(3)Br (R(4)). Six-parameter Arrhenius expressions have been obtained by fitting to the computed rate constants of these four reactions (including cis and trans pathways) over the temperature range of 300-2500 K.     

Substituent effects on the disproportionation-combination rate constant ratios for gas-phase halocarbon radicals. Part III: Reactions of CF3 + CF3CH2 CHCF3 and CF3 CH2CHCF3 + CF3CH2 CHCF3

Disproportionation/combination rate constant ratios, k_d/k_c, for the reactive collision between CF₃CH₂CHX + CF₃ radicals and between CF₃CH₂CHX + CF₃CH₂CHX radicals have been measured for X = CF₃. The k_d/k_c = 0.066 ± 0.013 when H is transferred to the CF₃ radical and 0.125 ± 0.025 for H transfer to the CF₃CH₂CHCF₃ radical. Comparison of these results with previous work shows that X = CF₃ increases the k_c/k_c' s relative to X = Cl or H. The effect of the CF₃ substituent on the disproportionation rate is discussed. © 1996 John Wiley & Sons, Inc.     

Kinetic and mechanistic study of the reactions of atomic chlorine with CH3CH2Br, CH3CH2CH2Br, and CH2BrCH2Br

A laser flash photolysis-resonance fluorescence technique has been employed to investigate the reactions of atomic chlorine with three alkyl bromides (R-Br) that have been identified as short-lived atmospheric constituents with significant ozone depletion potentials (ODPs). Kinetic data are obtained through time-resolved observation of the appearance of atomic bromine that is formed by rapid unimolecular decomposition of radicals generated via abstraction of a β-hydrogen atom. The following Arrhenius expressions are excellent representations of the temperature dependence of rate coefficients measured for the reactions Cl + CH(3)CH(2)Br (eq 1 ) and Cl + CH(3)CH(2)CH(2)Br (eq 2 ) over the temperature range 221-436 K (units are 10(-11) cm(3) molecule(-1) s(-1)): k(1)(T) = 3.73?exp(-378/T) and k(2)(T) = 5.14?exp(+21/T). The accuracy (2σ) of rate coefficients obtained from the above expressions is estimated to be ±15% for k(2)(T) and +15/-25% for k(1)(T) independent of T. For the relatively slow reaction Cl + CH(2)BrCH(2)Br (eq 3 ), a nonlinear ln k(3) vs 1/T dependence is observed and contributions to observed kinetics from impurity reactions cannot be ruled out; the following modified Arrhenius expression represents the temperature dependence (244-569 K) of upper-limit rate coefficients that are consistent with the data: k(3)(T) ≤ 3.2 × 10(-17)T(2)?exp(-184/T) cm(3) molecule(-1) s(-1). Comparison of Br fluorescence signal strengths obtained when Cl removal is dominated by reaction with R-Br with those obtained when Cl removal is dominated by reaction with Br(2) (unit yield calibration) allows branching ratios for β-hydrogen abstraction (k(ia)/k(i), i = 1,2) to be evaluated. The following Arrhenius-type expressions are excellent representations of the observed temperature dependences: k(1a)/k(1) = 0.85?exp(-230/T) and k(2a)/k(2) = 0.40 exp(+181/T). The accuracy (2σ) of branching ratios obtained from the above expressions is estimated to be ±35% for reaction 1 and ±25% for reaction 2 independent of T. It appears likely that reactions 1 and 2 play a significant role in limiting the tropospheric lifetime and, therefore, the ODP of CH(3)CH(2)Br and CH(3)CH(2)CH(2)Br, respectively.     

Theoretical study of the reactions of CF3OCHF2 with the hydroxyl radical and the chlorine atom.

Theoretical investigations are carried out on the reaction mechanism of the reactions of CF3OCHF2 (HFOC-125) with the OH radials and Cl atoms, as well as the heats of formation of CF3OCHF2 and CF3OCF2. The electronic structure information on the potential energy surface for each reaction is obtained at the B3LYP/6-311G(d,p) level, and energetic information is further refined by G3(MP2) theory. The direct dynamics calculation of the hydrogen abstraction reactions are also performed at the G3(MP2)//B3LYP/ 6-311G(d,p) level. The classical energy profile is corrected by interpolated single-point energies (ISPE) approach, incorporating the small-curvature tunnelling effect (SCT) calculated by the variational transition-state theory (VTST). The rate constants are in good agreement with the experimental data and are found to be k1 = 4.95 x 10(-30)T(5.40)exp(-347/T) and k2 = 1.86 x 10(-23)T(3.43)exp(-1579/T) cm3 molecule(-1)s(-1) over the temperature range 200-2000 K. The rate constants at 298 K for these two reactions are 3.38 x 10(-16) and 2.80 x 10(-17) cm3 molecule(-1)s(-1), respectively. Using group-balanced isodesmic reactions as working chemical reactions, the standard enthalpies of formation for CF3OCHF2 and CF3OCF2 are -312.3 +/- 1.0 and -257.3 +/- 1.0 kcalmol(-1), respectively, evaluated by G3(MP2) theory based on the B3LYP/6-311G(d,p) geometries. The theoretical studies provide rate constants of the title reactions and the enthalpies of the species, which are important parameters in determining the atmospheric lifetime and the feasible pathways for the loss of HFOC-125.     

Substituent effects on the disproportionation-combination rate constant ratios for gas-phase halocarbon radicals. II. Reactions of •CF3 +CF3CH2CH2• and CF3CH2CH2• + CF3CH2CH2•

Disproportionation/combination rate constant ratios, k_d /k_c, have been measured for the collision between CF₃CH₂CH₂ and CF₃ radicals to be 0.022 ± 0.002 and for CF₃CH₂CH₂ and CF₃CH₂CH₂ radicals to be 0.100 ± 0.002. Comparison to previous work from this laboratory for the reaction of CF₃CH₂CHCl with CF₃ radicals shows that substitution of Cl for H increases the k_d /k_c by about 50%; however, for the auto disproportionation-combination of CF₃CH₂CH₂ radicals the chlorine substituent decreases the observed rate constant ratio by a factor of two. The chlorine substituent effect on the observed k_d /k_c ratios is compared to predictions from molecular orbital calculations. © 1996 John Wiley & Sons, Inc.     

Rate constants and Arrhenius parameters for the reactions of Cl atoms with the halogenated ethers: CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2

Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF₃CH₂OCHF₂, CF₃CHClOCHF₂, and CF₃CH₂OCClF₂ using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl₂ in a mixture containing the ether and CD₄. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD₄ → DCl + CD₃. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF₃CH₂OCHF₂: k = (5.1₅ ± 0.7) × 10⁻¹² exp(−1830 ± 410 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CHClOCHF₂: k = (1.6 ± 0.2) × 10⁻¹¹ exp(−2450 ± 250 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CH₂OCClF₂: k = (9.6 ± 0.4) × 10⁻¹² exp(−2390 ± 190 K/T) cm³ molecule⁻¹ s⁻¹ The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001     

Kinetics of gas‐phase reactions of CH3OCH2CF3, CH3OCH3, CH3OCH2CH3, CH3CH2OCH2CH3, and CHF2CF2OCH2CF3 with NO3 radicals at 298 K

Rate constants for the gas‐phase reactions of CH₃OCH₂CF₃ (k₁), CH₃OCH₃ (k₂), CH₃OCH₂CH₃ (k₃), and CH₃CH₂OCH₂CH₃ (k₄) with NO₃ radicals were determined by means of a relative rate method at 298 K. NO₃ radicals were prepared by thermal decomposition of N₂O₅ in a 700–750 Torr N₂O₅/NO₂/NO₃/air gas mixture in a 1‐m³ temperature‐controlled chamber. The measured rate constants at 298 K were k₁ = (5.3 ± 0.9) × 10^?18, k₂ = (1.07 ± 0.10) × 10^?16, k₃ = (7.81 ± 0.36) × 10^?16, and k₄ = (2.80 ± 0.10) × 10^?15 cm³ molecule^?1 s^?1. Potential energy surfaces for the NO₃ radical reactions were computationally explored, and the rate constants of k₁–k₅ were calculated according to the transition state theory. The calculated values of rate constants k₁–k₄ were in reasonable agreement with the experimentally determined values. The calculated value of k₅ was compared with the estimate (k₅ < 5.3 × 10^?21 cm³ molecule^?1 s^?1) derived from the correlation between the rate constants for reactions with NO₃ radicals (k₁–k₄) and the corresponding rate constants for reactions with OH radicals. We estimated the tropospheric lifetimes of CH₃OCH₂CF₃ and CHF₂CF₂OCH₂CF₃ to be 240 and >2.4 × 10⁵ years, respectively, with respect to reaction with NO₃ radicals. The tropospheric lifetimes of these compounds are much shorter with respect to the OH reaction. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 490–497, 2009