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     

Absolute rate constants for the self reactions of HO2, CF3CFHO2, and CF3O2 radicals and the cross reactions of HO2 with FO2, HO2 with CF3CFHO2, and HO2 with CF3O2 at 295 K

The kinetics of the self-reactions of HO₂, CF₃CFHO₂, and CF₃O₂ radicals and the cross reactions of HO₂ with FO₂, HO₂ with CF₃CFHO₂, and HO₂ with CF₃O₂ radicals, were studied by pulse radiolysis combined with time resolved UV absorption spectroscopy at 295 K. The rate constants for these reactions were obtained by computer simulation of absorption transients monitored at 220, 230, and 240 nm. The following rate constants were obtained at 295 K and 1000 mbar total pressure of SF₆ (unit: 10⁻¹² cm³ molecule⁻¹ s⁻¹): k(HO₂+HO₂)=3.5±1.0, k(CF₃CFHO₂+CF₃CFHO₂)=3.5±0.8, k(CF₃O₂+CF₃O₂)=2.25±0.30, k(HO₂+FO₂)=9±4, k(CF₃CFHO₂+HO₂)=5.0±1.5, and k(CF₃O₂+HO₂)=4.0±2.0. In addition, the decomposition rate of CF₃CFHO radicals was estimated to be (0.2–2)×10³ s⁻¹ in 1000 mbar of SF₆. Results are discussed in the context of the atmospheric chemistry of hydrofluorocarbons. © 1997 John Wiley & Sons, Inc.     

The dark reactions F2 + CF3I,C2F5I,and n-C3F7I

The reactions between F₂ and the lowest members of the homologous series of perfluoroalkyl iodides (CF₃I, C₂F₅I, and n-C₃F₇I) have been studied. For these compounds, an exponential decrease in the alkyl iodide concentration over time following an induction period is observed for certain experimental conditions. Other conditions lead to chaotic-like kinetic behavior where the rate of alkyl iodide consumption continually changes. Kinetic rate data with CF₃I show that the disappearance rate depends upon both the type of surface and surface preparation. For all three compounds, Arrhenius plots reveal activation energies on the order of 10 kcal/mol, consistent with effective initiation steps of F₂ + RI → RIF + F, where R represents the CF₃, C₂F₅, or n-C₃F₇ radical respectively. The end products of the F₂ + RI reactions are RF, R₂, and IF₅, suggesting that the R radicals play an important kinetic role. Introducing O₂ into the F₂ + RI reaction systems results in successive oxidation of R by O₂, leading to the formation of CF₂O as an additional end product. IF(B → X) emission is observed from the RI-rich F₂ + RI reactions, confirming the existence of IF as an intermediate. © 1996 John Wiley & Sons, Inc.     

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.     

UV absorption spectrum of CF3CFClO2 and kinetics of the self reaction of CF3CFCl and CF3CFClO2 and the reactions of CF3CFClO2 with NO and NO2

The ultraviolet absorption spectrum of CF₃CFClO₂ and the kinetics of the self reactions of CF₃CFCl and CF₃CFClO₂ radicals and the reactions of CF₃CFClO₂ with NO and NO₂ have been studied in the gas phase at 295 K by pulse radiolysis/transient UV absorption spectroscopy. The UV absorption cross section of CF₃CFCl radicals was measured to be (1.78 ± 0.22) × 10^?18 cm² molecule^?1 at 220 nm. The UV spectrum of CF₃CFClO₂ radicals was quantified from 220 nm to 290 nm. The absorption cross section at 250 nm was determined to be (1.67 ± 0.21) × 10^?18 cm² molecule^?1. The rate constants for the self reactions of CF₃CFCl and CF₃CFClO₂ radicals were (2.6 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1 and (2.6 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. The reactivity of CF₃CFClO₂ radicals towards NO and NO₂ was determined to (1.5 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 and (5.9 ± 0.5) × 10^?12 cm³ molecule^?1 s^?1, respectively. Finally, the rate constant for the reaction of F atoms with CF₃CFClH was determined to (8 ± 2) × 10^?13 cm³ molecule^?1 s^?1. Results are discussed in the context of the atmospheric chemistry of HCFC-124, CF₃CFClH. © 1994 John Wiley & Sons, Inc.     

Substituent effects on the disproportionation‐combination rate constant ratios for gas‐phase halocarbon radicals. IV. Reactions of ·CF3 + CF3CH2CF2· and CF3CH2CF2· + CF3CH2CF2·

Rate constant ratios, k_d/k_c, for the disproportionation/combination reaction at a temperature of 295 ± 2 K, have been measured as 0.034 ± 0.009 for the collision between CF₃CH₂CF₂ + CF₃ radicals and as 0.075 ± 0.019 for CF₃CH₂CF₂ + CF₃CH₂CF₂ radicals. The effect of the two fluorine substituents on the rate constant ratio is compared to previous k_d/k_cs with CF₃CH₂CH₂, CF₃CH₂CHCl, and CF₃CH₂CHCF₃ radicals. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 237–243, 1999     

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.     

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     

Relative rate constants for reactions of HFC 152a, 143, 143a, 134a,and HCFC 124 with F or Cl atoms and for CF2CH3, CF2HCH2, and CF3CFH radicals with F2, Cl2, and O2

Relative rate experiments using UV photolysis of F₂ or Cl₂ have been used to determine rate constant ratios for several hydrofluorocarbon (HFC) reactions with Cl or F atoms and for HFC alkyl radicals with molecular halogens. For mixtures with F₂ present, dark reactions are, also, observed which are attributed to thermal dissociation of the F₂ to form F atoms. At 296 K, the rate of reaction (1a) [CF₂HCH₃ + F → CF₂CH₃ + HF] relative to (1b) [CF₂HCH₃ + F → CF₂HCH₂ + HF] is k_1a/k_1b = 0.73 (±0.13) and is independent of T (= 262–348 K). At 296 K, the ratio of reaction (2a) [CF₂HCH₂F + F → products] to that of (k_1a + k_1b) is (k_1a + k_1b)/k_2a = 2.7 (±0.4), and for reaction (2b) [CF₃CH₃ + F → products] (k_1a + k_1b)/k_2b = 22 ± 12. The temperature dependence (263–365 K) of the rate constant of reaction (3) [CF₃CFH₂ + Cl → products] relative to reaction (4) [CF₃CFClH + Cl → products] is k₃/k₄(±10%) = 1.55 exp(?300 K/T). For the alkyl radicals formed from HFC 152a (CF₂HCH₂ and CF₂CH₃) and from HFC 134a (CF₃CFH), rate constants for the reactions with F₂ and Cl₂ were measured relative to their reactions with O₂. The rate constant of reaction (5cl) [CF₂CH₃ + Cl₂ → CF₂ClCH₃ + Cl] relative to (5o) [CF₂CH₃ + O₂ → CF₂(O₂)CH₃] is k_5cl/k_5o(±15%) = 0.3 exp(200 K/T). For reaction (5f) [CF₂CH₃ + F₂ → CF₃CH₃ + F], k_5f/k_5o(±35%) = 0.23. The ratio for reaction (6f) [CF₂HCH₂ + F₂ → CF₂HCH₂F + F] relative to (6o) [CF₂HCH₂ + O₂ → CF₂HCH₂O₂] is k_6f/k_6o(±40%) = 1.23 exp(?730 K/T). The rate constant ratio for reaction (8cl) [CF₃CFH + Cl₂ → CF₃CFClH + Cl] relative to reaction (8o) [CF₃CFH + O₂ → CF₃CFHO₂] is k_8cl/k_8o(±18%) = 0.16 exp(?940 K/T). For reaction (8f) [CF₃CFH + F₂ → CF₃CF₂H + F], k_8f/k_8o(±35%) = 0.6 exp(?860 K/T). © 1993 John Wiley & Sons, Inc.     

Hydrogen abstraction from CF3CF2CFH2 and CF3CFHCF2H by OH radicals and Cl atoms: theoretical enthalpies and rate constants

The hydrogen abstraction reactions of CF₃CF₂CFH₂ and CF₃CFHCF₂H with OH radicals and Cl atoms have been studied theoretically by a dual-level direct dynamics method. Two stable conformers of CF₃CF₂CFH₂ with C _s and C ₁ symmetries and all possible abstraction channels for each reaction are all taken into consideration. Optimized geometries and frequencies of all the stationary points and extra points along minimum-energy path (MEP) have been computed at the BB1K/6-31+G(d, p) level of theory. To refine the energy profile of each reaction channel, single point energy calculations have been performed by the BMC-CCSD method. The rate constants are evaluated by canonical variational transition state theory (CVT) with the small-curvature tunneling correction method (SCT) over a wide temperature range of 200–1,000 K. The detailed branching ratios of four reactions are discussed. The good agreement found between our theoretical rate constants and the available experimental data suggests that the present approach could provide a reliable prediction for the CF₃CFHCF₂H + Cl reaction about which there is little experimental information. The kinetic calculations show that the SCT effect plays an important role in all channels. In addition, in order to further reveal the thermodynamic properties, the enthalpies of formation of the reactants (CF₃CF₂CFH₂ and CF₃CFHCF₂H) and the product radicals (CF₃CF₂CFH, CF₃CFCF₂H, and CF₃CFHCF₂) are evaluated by applying isodesmic reactions at both BMC-CCSD//BB1K/6-31+G(d, p) and MC-QCISD//BB1K/6-31+G(d, p) levels of theory.     

Photolysis of CF3NO as a source of CF3 radicals,rate constant of the CF3 + CF3NO reaction at 296 K

The linear absorption cross-sections and photodissociation quantum yields for CF₃NO have been measured at the wavelengths 694.3 and 632.8 nm (ruby and He(SINGLEBOND)Ne lasers, respectively) in a wide range of total pressure at T = 296 K. The secondary reactions following the photolysis of CF₃NO have been studied. The rate constant of the CF₃ + CF₃NO reaction has been measured. The results obtained show CF₃NO photolysis be a convenient source of CF₃ radicals for kinetic studies. © 1996 John Wiley & Sons, Inc.     

Kinetic study of gas-phase reactions with CF2Cl2 and CFCl3. Analysis using the transition state theory (TST) of the chlorine atom transfer reactions by CF3 and CH3 radicals from halomethanes

The following gas-phase reactions: were studied by the competitive method with CF₃I as the source of radicals. The kinetic parameters obtained in the temperature range 533–613 K and 503–613 K respectively for chlorine atom transfer reactions are given by: where θ = 2.303 RT (cal mol^?1). The Arrhenius A values were calculated for seven chlorine atom transfer reactions (CF₂Cl₂, CFCl₃, CCl₄ with CF₃ radicals; CF₃Cl, CF₂Cl₂, CFCl₃ and CCl₄ with CH₃ radicals) by using the thermochemical kinetic version of the Transition State Theory (TST).     

Long path-FTIR studies of some atmospheric reactions involving CF3OO and CF3O radicals

In attempts to obtain kinetic and mechanistic data required for an assessment of atmospheric fate of alternative halocarbons containing a CF₃ group, reactions of the key free radical intermediates CF₃OO and CF₃O with several atmospheric compounds (i.e., NO, NO₂, alkanes and alkenes) have been studied at 297 ± 2 K in 700 torr of air. Experiments employed the long path-FTIR spectroscopic method for product analysis and the visible (400 nm) photolysis of CF₃NO → CF₃ + NO as a source for the precursor radical CF₃. Numerous labile and stable F-containing molecular products have been characterized based on kinetic and spectroscopic data obtained at sufficiently short photolysis time (≤1 min) to minimize heterogeneous decay on the reactor walls. Major new findings have been made for the reactions involving CF₃O radicals. The behavior of CF₃O radicals has been shown to be markedly different from that of CH₃O radicals, i.e., (1) O₂-reaction: no evidence for the F-atom transfer reaction CF₃O + O₂ → CF₂ O + FOO; (2) NO-reaction: addition reaction CH₃O + NO (+M) → CH₃ONO (+M), but F-transfer reaction CF₃O + NO → CF₂O + FNO; (3) NO₂-reaction: addition reaction for both radicals, but F-transfer reaction CF₃ + NO₂ → CF₂O + FNO₂ to a minor extent; (4) alkane-reaction: much faster H-abstraction by CF₃O, comparable to HO; (5) alkene-reaction: much faster addition reaction of CF₃O, comparable to HO. These results are summarized in this paper.     

Thermal Decomposition of CF3C(O)O2NO2, CClF2C(O)O2NO2, CCl2FC(O)O2NO2, and CCl3C(O)O2NO2

Haloacetyl, peroxynitrates are intermediates in the atmospheric degradation of a number of haloethanes. In this work, thermal decomposition rate constants of CF₃C(O)O₂NO₂, CClF₂C(O)O₂NO₂, CCl₂FC(O)O₂NO₂, and CCl₃C(O)O₂NO₂ have been determined in a temperature controlled 420 l reaction chamber. Peroxynitrates (RO₂NO₂) were prepared in situ by photolysis of RH/Cl₂/O₂/NO₂/N₂ mixtures (R = CF₃CO, CClF₂CO, CCl₂FCO, and CCl₃CO). Thermal decomposition was initiated by addition of NO, and relative RO₂NO₂ concentrations were measured as a function of time by long-path IR absorption using an FTIR spectrometer. First-order decomposition rate constants were determined at atmospheric pressure (M = N₂) as a function of temperature and, in the case of CF₃C(O)O₂NO₂ and CCl₃C(O)O₂NO₂, also as a function of total pressure. Extrapolation of the measured rate constants to the temperatures and pressures of the upper troposphere yields thermal lifetimes of several thousands of years for all of these peroxynitrates. Thus, the chloro(fluoro)acetyl peroxynitrates may play a role as temporary reservoirs of Cl, their lifetimes in the upper troposphere being limited by their (unknown) photolysis rates. Results on the thermal decomposition of CClF₂CH₂O₂NO₂ and CCl₂FCH₂O₂NO₂ are also reported, showing that the atmospheric lifetimes of these peroxynitrates are very short in the lower troposphere and increase to a maximum of several days close to the tropopause. The ratio of the rate constants for the reactions of CF₃C(O)O₂ radicals with NO₂ and NO was determined to be 0.64 ± 0.13 (2σ) at 315 K and a total pressure of 1000 mbar (M = N₂). © 1994 John Wiley & Sons, Inc.     

Kinetics for the gas‐phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268–308 K

Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH₂FCF₂OCHF₂(k₁), CHF₂CF₂OCH₂CF₃ (k₂), CF₃CHFCF₂OCH₂CF₃(k₃), and CF₃CHFCF₂OCH₂CF₂CHF₂(k₄) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE–reference–H₂O–O₃–O₂–He gas mixture in a 1‐m³ temperature‐controlled chamber. By using CH₄, CH₃CCl₃, CHF₂Cl, and CF₃CF₂CF₂OCH₃ as the reference compounds, reaction rate constants of OH radicals of k₁ = (1.68) × 10^?12 exp[(?1710 ± 140)/T], k₂ = (1.36) × 10^?12 exp[(?1470 ± 90)/T], k₃ = (1.67) × 10^?12 exp[(?1560 ± 140)/T], and k₄ = (2.39) × 10^?12 exp[(?1560 ± 110)/T] cm³ molecule^?1 s^?1 were obtained at 268–308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k₁–k₄. The results are discussed in relation to the predictions of Atkinson's structure–activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH₂FCF₂OCHF₂, CHF₂CF₂OCH₂CF₃, CF₃CHFCF₂OCH₂CF₃, and CF₃CHFCF₂OCH₂CF₂CHF₂, respectively, by scaling from the lifetime of CH₃CCl₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239–245, 2003     

Discharge flow‐chemiluminescence study of the rate coefficients for O(3P) + CF2CCl2 and O(3P) + CF3CFCF2 reactions at 298 K

The kinetics of the reactions O(³P) + CF₂CCl₂ and O(³P) + CF₃CFCF₂ were studied at room temperature in a discharge flow tube system. The overall rate constants based on the measured afterglow reactions were (3.10 ± 0.40) × 10⁻¹³ and (3.00 ± 0.60) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, respectively. The experiments were carried out under pseudo‐first‐order conditions with [O(³P)]₀ ≪ [alkene]₀. These results are compared with previous relative measurements using different experimental techniques. The effect of substituent atoms or groups on the overall rate constants is analyzed in comparison with other alkenes in the literature. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 867–872, 1999     

Kinetics and mechanism of the addition of trichloromethyl radicals to chloroethylenes. The addition to CIS-C2Cl2H2, trans-C2Cl2H2, and C2Cl3H

The addition reactions of CCl₃ radicals with cis-C₂Cl₂H₂, trans-C₂Cl₂H₂, and C₂Cl₃H in liquid cyclohexane–CCl₄ mixtures were studied between 323 and 448 K. The Arrhenius parameters of these reactions were competitively determined versus H-atom transfer from cyclohexane and addition to C₂Cl₄. The present data and the data obtained in previous liquid and gas phase studies show that the reactivities displayed in addition reactions of different radicals with chloroethylenes reflect primarily variations in activation energies rather than in A factors. The activation energies for the addition of CCl₃, CF₃, and CH₃ radicals to chloroethylenes appear, to a large extent, to be determinedby the stability of the adduct radicals. Comparison of the reactivity trends in the addition reactions of chloro- and fluoro-substitutedethylenes indicates that these two electron-withdrawing substituentshave a converse effect on the reactivity of electrophilic radicals. This behavior is ascribed to the strong mesomeric effect of vinylic chlorosubstituents.     

Rate constants for the gas‐phase reaction of CF3CF2CF2CF2CF2CHF2 with OH radicals at 250–430 K

The rate constants k₁ for the reaction of CF₃CF₂CF₂CF₂CF₂CHF₂ with OH radicals were determined by using both absolute and relative rate methods. The absolute rate constants were measured at 250–430 K using the flash photolysis–laser‐induced fluorescence (FP‐LIF) technique and the laser photolysis–laser‐induced fluorescence (LP‐LIF) technique to monitor the OH radical concentration. The relative rate constants were measured at 253–328 K in an 11.5‐dm³ reaction chamber with either CHF₂Cl or CH₂FCF₃ as a reference compound. OH radicals were produced by UV photolysis of an O₃–H₂O–He mixture at an initial pressure of 200 Torr. Ozone was continuously introduced into the reaction chamber during the UV irradiation. The k₁ (298 K) values determined by the absolute method were (1.69 ± 0.07) × 10^?15 cm³ molecule^?1 s^?1 (FP‐LIF method) and (1.72 ± 0.07) × 10^?15 cm³ molecule^?1 s^?1 (LP‐LIF method), whereas the K₁ (298 K) values determined by the relative method were (1.87 ± 0.11) × 10^?15 cm³ molecule^?1 s^?1 (CHF₂Cl reference) and (2.12 ± 0.11) × 10^?15 cm³ molecule^?1 s^?1 (CH₂FCF₃ reference). These data are in agreement with each other within the estimated experimental uncertainties. The Arrhenius rate constant determined from the kinetic data was K₁ = (4.71 ± 0.94) × 10^?13 exp[?(1630 ± 80)/T] cm³ molecule^?1 s^?1. Using kinetic data for the reaction of tropospheric CH₃CCl₃ with OH radicals [k₁ (272 K) = 6.0 × 10^?15 cm³ molecule^?1 s^?1, tropospheric lifetime of CH₃CCl₃ = 6.0 years], we estimated the tropospheric lifetime of CF₃CF₂CF₂CF₂CF₂CHF₂ through reaction with OH radicals to be 31 years. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 36: 26–33, 2004     

Reaction of CF3 radicals with H2S

Hydrogen abstration from H₂S by CF₃ radicals, generated by the photolysis of both CF₃COCF₃ and CF₃I, has been studied in the temperature range 314–434 K. The rate constant, based on the value of 10^13.36 cm³/mol · s for the recombination of CF₃ radicals, is given by with CF₃COCF₃ as the radical source, and with CF₃I as the radical source, where k₂ is in cm³/mol · s and E is in J/mol. These results resolve a previously existing controversy concerning the values of the rate constants for this reaction. They show that CF₃ radicals are less reactive than CH₃ radicals in attacking H₂S, and this behavior indicates that polar effects play a significant role in the hydrogen transfer reactions of CF₃ radicals.