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     

Rate constants for the reactions of chlorine atoms with hydrochloroethers at 298 k and atmospheric pressure

The relative rate technique has been used to determine the rate constants for the reactions Cl + CH₃OCHCl₂ → products and Cl + CH₃OCH₂CH₂Cl → products. Experiments were carried out at 298 ± 2 K and atmospheric pressure using nitrogen as the bath gas. The decay rates of the organic species were measured relative to those of 1,2‐dichloroethane, acetone, and ethane. Using rate constants of (1.3 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1, (2.4 ± 0.4) × 10^?12 cm³ molecule^?1 s^?1, and (5.9 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1 for the reactions of Cl atoms with 1,2‐dichloroethane, acetone, and ethane respectively, the following rate coefficients were derived for the reaction of Cl atoms (in units of cm³ molecule^?1 s^?1) with CH₃OCHCl₂, k= (1.04 ± 0.30) × 10^?12 and CH₃OCH₂CH₂Cl, k= (1.11 ± 0.20) × 10^?10. Errors quoted represent two σ, and include the errors due to the uncertainties in the rate constants used to place our relative measurements on an absolute basis. The rate constants obtained are compared with previous literature data and used to estimate the atmospheric lifetimes for the studied ethers. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 420–426, 2005     

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 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.     

1,1,1,3,3,-pentafluorobutane (HFC-365mfc): atmospheric degradation and contribution to radiative forcing

The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3-pentafluorobutane (HFC-365mfc) has been determined over the temperature range 278–323K using a relative rate technique. The results provide a value of k(OH+CF₃CH₂CF₂CH₃)=2.0×10⁻¹²exp(−1750±400/T) cm³ molecule⁻¹ s⁻¹ based on k(OH+CH₃CCl₃)=1.8×10⁻¹² exp (−1550±150/T) cm³ molecule⁻¹ s⁻¹ for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC-365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3-pentafluorobutane was also determined at 298±2 K using the relative rate method, k(Cl+CF₃CH₂CF₂CH₃)=(1.1±0.3)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. The chlorine initiated photooxidation of CF₃CH₂CF₂CH₃ was investigated from 273–330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon-containing products were CF₂O and CO₂, with smaller amounts of CF₃O₃CF₃. In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH₂(SINGLE BOND) and (SINGLE BOND)CH₃ groups in CF₃CH₂CF₂CH₃, rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF₃CH₂CCl₂F and CF₃CH₂CF₃ were also determined at 298 K k(OH+CF₃CH₂CCl₂F)=(8±3)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(OH+CF₃CH₂CF₃)=(3.5±1.5)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(Cl+CF₃CH₂CCl₂F)=(3.5±1.5)×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹]; k(Cl+CF₃CH₂CF₃)<1×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹. The results indicate that the most probable site for H-atom abstraction from CF₃CH₂CF₂CH₃ is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross-sections have been measured for CF₃CH₂CF₂CH₃, and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical-radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady-state Halocarbon Global Warming Potential, relative to CFC-11, is 0.17. The Global Warming Potentials relative to CO₂ are found to be 2210, 790, and 250, for integration time-horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.     

Kinetics and mechanism for the atmospheric oxidation of 1,1,2-trifluoroethane (HFC 143)

The rate constant for the reaction of the hydroxyl radical with 1,2,2-trifuoroethane has been determined over the temperature range 278–323 K using a relative rate technique. The results provide a value of k(OH + CH₂FCHF₂) = 2.65 × 10^?12 exp(?1542 ± 500/T) cm³ molecule^?1 s^?1 based on k(OH + CH₃CCl₃) = 1.2 × 10^?12 exp(?1400 ± 200/T) cm³ molecule^?1 s^?1 for the rate constant of the reference reaction. The chlorine atom initiated photooxidation of CH₂CHF₂ was investigated from 255 to 330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. The major carbon-containing products were CHFO and CF₂O suggesting that the alkoxy radicals CH₂FCF₂O and CHF₂CHFO, formed in the reaction, react predominantly by carbon-carbon bond cleavage. The results indicate that formation of CHF₂CFO from the reaction of CHF₂CHFO radicals with O₂ will be unimportant under all atmospheric conditions. © 1995 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     

New technique for generating high concentrations of gaseous OH radicals in relative rate measurements

We have developed a technique for generating high concentrations of gaseous OH radicals in a reaction chamber. The technique, which involves the UV photolysis of O₃ in the presence of water vapor, was used in combination with the relative rate method to obtain rate constants for reactions of OH radicals with selected species. A key improvement of the technique is that an O₃/O₂ (3%) gas mixture is continuously introduced into the reaction chamber, during the UV irradiation period. An important feature is that a high concentration of OH radicals [(0.53–1.2) × 10¹¹ radicals cm^?3] can be produced during the irradiation in continuous, steady‐state experiment. Using the new technique in conjunction with the relative rate method, we obtained the rate constant for the reaction of CHF₃ (HFC‐23) with OH radicals, k₁. We obtained k₁(298 K) = (3.32 ± 0.20) × 10^?16 and determined the temperature dependence of k₁ to be (0.48 ± 0.13) × 10^?12 exp[?(2180 ± 100)/T] cm³ molecule^?1 s^?1 at 253–328 K using CHF₂CF₃ (HFC‐125) and CHF₂Cl (HCFC‐22) as reference compounds in CHF₃–reference–H₂O gas mixtures. The value of k₁ obtained in this study is in agreement with previous measurements of k₁. This result confirms that our technique for generating OH radicals is suitable for obtaining OH radical reaction rate constants of ～10^?16 cm³ molecule^?1 s^?1, provided the rate constants do not depend on pressure. In addition, it also needed to examine whether the reactions of sample and reference compound with O₃ interfere the measurement when selecting this technique. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 317–325, 2003     

Kinetics and mechanism of atmospheric reactions of partially fluorinated alcohols

Gas-phase reactions typical of the Earth’s atmosphere have been studied for a number of partially fluorinated alcohols (PFAs). The rate constants of the reactions of CF₃CH₂OH, CH₂FCH₂OH, and CHF₂CH₂OH with fluorine atoms have been determined by the relative measurement method. The rate constant for CF₃CH₂OH has been measured in the temperature range 258–358 K (k = (3.4 ± 2.0) × 10¹³exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(1.5 ± 1.3) kJ/mol). The rate constants for CH₂FCH₂OH and CHF₂CH₂OH have been determined at room temperature to be (8.3 ± 2.9) × 10¹³ (T = 295 K) and (6.4 ± 0.6) × 10¹³ (T = 296 K) cm³ mol^?1 s^?1, respectively. The rate constants of the reactions between dioxygen and primary radicals resulting from PFA + F reactions have been determined by the relative measurement method. The reaction between O₂ and the radicals of the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH) have been investigated in the temperature range 258–358 K to obtain k = (3.8 ± 2.0) × 10⁸exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(10.2 ± 1.5) kJ/mol. For the reaction between O₂ and the radicals of the general formula C₂H₄FO (? HFCH₂O, CH₂F?HOH, and CH₂FCH₂?) at T = 258–358 K, k = (1.3 ± 0.6) × 10¹¹exp(?E/RT) cm³ mol^?1 s^?1, where E = ?(5.3 ± 1.4) kJ/mol. The rate constant of the reaction between O₂ and the radicals with the general formula C₂H₃F₂O (?F₂CH₂O, CHF₂?HOH, and CHF₂CH₂?) at T = 300 K is k = 1.32 × 10¹¹ cm³ mol^?1 s^?1. For the reaction between NO and the primary radicals with the general formula C₂H₂F₃O (CF₃CH₂? and CF₃?HOH), which result from the reaction CF₃CH₂OH + F, the rate constant at 298 K is k = 9.7 × 10⁹ cm³ mol^?1 s^?1. The experiments were carried out in a flow reactor, and the reaction mixture was analyzed mass-spectrometrically. A mechanism based on the results of our studies and on the literature data has been suggested for the atmospheric degradation of PFAs.     

Temperature‐dependent rate coefficients and mechanism for the gas‐phase reaction of chlorine atoms with acetone

The rate coefficient for the gas‐phase reaction of chlorine atoms with acetone was determined as a function of temperature (273–363 K) and pressure (0.002–700 Torr) using complementary absolute and relative rate methods. Absolute rate measurements were performed at the low‐pressure regime (～2 mTorr), employing the very low pressure reactor coupled with quadrupole mass spectrometry (VLPR/QMS) technique. The absolute rate coefficient was given by the Arrhenius expression k(T) = (1.68 ± 0.27) × 10^?11 exp[?(608 ± 16)/T] cm³ molecule^?1 s^?1 and k(298 K) = (2.17 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are the 2σ (95% level of confidence), including estimated systematic uncertainties. The hydrogen abstraction pathway leading to HCl was the predominant pathway, whereas the reaction channel of acetyl chloride formation (CH₃C(O)Cl) was determined to be less than 0.1%. In addition, relative rate measurements were performed by employing a static thermostated photochemical reactor coupled with FTIR spectroscopy (TPCR/FTIR) technique. The reactions of Cl atoms with CHF₂CH₂OH (3) and ClCH₂CH₂Cl (4) were used as reference reactions with k₃(T) = (2.61 ± 0.49) × 10^?11 exp[?(662 ± 60)/T] and k₄(T) = (4.93 ± 0.96) × 10^?11 exp[?(1087 ± 68)/T] cm³ molecule^?1 s^?1, respectively. The relative rate coefficients were independent of pressure over the range 30–700 Torr, and the temperature dependence was given by the expression k(T) = (3.43 ± 0.75) × 10^?11 exp[?(830 ± 68)/T] cm³ molecule^?1 s^?1 and k(298 K) = (2.18 ± 0.03) × 10^?12 cm³ molecule^?1 s^?1. The quoted errors limits (2σ) are at the 95% level of confidence and do not include systematic uncertainties. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 724–734, 2010     

Kinetics and products of the gas-phase reactions of the OH radical and O3 with allyl chloride and benzyl chloride at room temperature

The kinetics of the gas-phase reactions of allyl chloride and benzyl chloride with the OH radical and O₃ were investigated at 298 ± 2 K and atmospheric pressure. Direct measurements of the rate constants for reactions with ozone yielded values of ??(O₃ + allyl chloride) = (1.60 ± 0.18) × 10^?18 cm³ molecule^?1 s^?1 and ??(O₃ + benzyl chloride) < 6 × 10^?20 cm³ molecule^?1 s^?1. With the use of a relative rate technique and ethane as a scavenger of chlorine atoms produced in the OH radical reactions, rate constants of ??(OH + allyl chloride) = (1.69 ± 0.07) × 10^?11 cm³ molecule^?1 s^?1 and ??(OH + benzyl chloride) = (2.80 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1 were measured. A study of the OH radical reaction with allyl chloride by long pathlength FT-IR absorption spectroscopy indicated that the co-products ClCH₂CHO and HCHO account for ca. 44% of the reaction, and along with the other products HOCH₂CHO, (ClCH₂)₂CO, and CH₂ ? CHCHO account for 84 ± 16% of the allyl chloride reacting. The data indicate that in one atmosphere of air in the presence of NO the chloroalkoxy radical formed following OH radical addition to the terminal carbon atom of the double bond decomposes to yield HOCH₂CHO and the CH₂Cl radical, which becomes a significant source of the Cl atoms involved in secondary reactions. A product study of the OH radical reaction with benzyl chloride identified only benzaldehyde and peroxybenzoyl nitrate in low yields (ca. 8% and ?4%, respectively), with the remainder of the products being unidentified.     

A kinetic study of the reaction of fluorine atoms with CH3F,CH3Cl,CH3Br,CF2H2, CO,CF3H,CF3CHCl2, CF3CH2F,CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K

A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm³ molecule^?1 s^?1: CH₃F, (3.7 ± 0.8) × 10^?11, CH₃Cl, (3.3 ± 0.7) × 10^?11; CH₃Br, (3.0 ± 0.7) × 10^?11; CF₂H₂, (4.3 ± 0.9) × 10^?12; CO, (5.5 ± 1.0) × 10^?13 (in 700 torr total pressure of N₂ diluent); CF₃H, (1.4 ± 0.4) × 10^?13; CF₃CCl₂H (HCFC-123), (1.2 ± 0.4) × 10^?12; CF₃CFH₂ (HFC-134a), (1.3 ± 0.3) × 10^?12, CHF₂CHF₂ (HFC-134), (1.0 ± 0.3) × 10^?12; CF₂ClCH₃ (HCFC-42b), (3.9 ± 0.9) × 10^?12, CF₂HCH₃ (HFC-152a), (1.7 ± 0.4) × 10^?11; and CF₃CF₂H (HFC-125), (3.5 ± 0.8) × 10^?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc.     

A laser flash photolysis/IR diode laser absorption study of the reaction of chlorine atoms with selected alkanes

A high‐resolution IR diode laser in conjunction with a Herriot multiple reflection flow‐cell has been used to directly determine the rate coefficients for simple alkanes with Cl atoms at room temperature (298 K). The following results were obtained: k(Cl + n‐butane) = (1.91 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐pentane) = (2.46 ± 0.12) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + iso‐pentane) = (1.94 ± 0.10) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + neopentane) = (1.01 ± 0.05) × 10^?10 cm³ molecule^?1 s^?1, k(Cl + n‐hexane) = (3.44 ± 0.17) × 10^?10 cm³ molecule^?1 s^?1 where the error limits are ±1σ. These values have been used in conjunction with our own previous measurements on Cl + ethane and literature values on Cl + propane and Cl + iso‐butane to generate a structure activity relationship (SAR) for Cl atom abstraction reactions based on direct measurements. The resulting best fit parameters are k_p = (2.61 ± 0.12) × 10^?11 cm³ molecule^?1 s^?1, k_s = (8.40 ± 0.60) × 10^?11 cm³ molecule^?1 s^?1, k_t = (5.90 ± 0.30) × 10^?11 cm³ molecule^?1 s^?1, with f( ? CH₂^? ) = f (? CH₂^? ) = f (?C?) = f = 0.85 ± 0.06. Tests were carried out to investigate the potential interference from production of excited state HCl(v = 1) in the Cl + alkane reactions. There is some evidence for HCl(v = 1) production in the reaction of Cl with shape n‐hexane. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 86–94, 2002     

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.     

Kinetics and mechanism for the oxidation of 1,1,1-trichloroethane

The reaction mechanisms for oxidation of CH₃CCl₂ and CCl₃CH₂ radicals, formed in the atmospheric degradation of CH₃CCl₃ have been elucidated. The primary oxidation products from these radicals are CH₃CClO and CCl₃CHO, respectively. Absolute rate constants for the reaction of hydroxyl radicals with CH₃CCl₃ have been measured in 1 atm of Argon at 359, 376, and 402 K using pulse radiolysis combined with UV kinetic spectroscopy giving ??(OH + CH₃CCl₃) = (5.4 ± 3) 10^?12 exp(?3570 ± 890/RT) cm³ molecule^?1 s^?1. A value of this rate constant of 1.3 × 10^?14 cm³ molecule^?1 s^?1 at 298 K was calculated using this Arrhenius expression. A relative rate technique was utilized to provide rate data for the OH + CH₃ CCl₃ reaction as well as the reaction of OH with the primary oxidation products. Values of the relative rate constants at 298 K are: ??(OH + CH₃CCl₃) = (1.09 ± 0.35) × 10^?14, ??(OH + CH₃CClO) = (0.91 ± 0.32) × 10^?14, ??(OH + CCl₃CHO) = (178 ± 31) × 10^?14, ??(OH + CCl₂O) < 0.1 × 10^?14; all in units of cm³ molecule^?1 s^?1. The effect of chlorine substitution on the reactivity of organic compounds towards OH radicals is discussed.     

Gas phase reaction of the hydroxyl radical with the unsaturated peroxyacyl nitrate CH2C(CH3)C(O)OONO2

The gas phase reaction of the hydroxyl radical with the unsaturated peroxyacyl nitrate CH₂ ? C(CH₃)C(O)OONO₂ (MPAN) has been studied at 298 ± 2 K and atmospheric pressure. The OH-MPAN reaction rate constant relative to that of OH + n-butyl nitrate is 2.08 ± 0.25. This ratio, together with a literature rate constant of 1.74 × 10^?12 cm³ molecule^?1 s^?1 for the OH + n-butyl nitrate reaction at 298 K, yields a rate constant of (3.6 ± 0.4)× 10^?12 cm³ molecule^?1 s^?1 for the OH-MPAN reaction at 298 ± 2 K. Hydroxyacetone and formaldehyde are the major carbonyl products. The yield of hydroxyacetone, 0.59 ± 0.12, is consistent with preferential addition of OH at the unsubstituted carbon atom. Atmospheric persistence and removal processes for MPAN are briefly discussed. © 1993 John Wiley & Sons, Inc.     

A kinetic and product study of reaction of chlorine atom with CH3CH2OD

The reaction of atomic chlorine with CH₃CH₂OD has been examined using a discharge fast flow system coupled to a mass spectrometer combined with the relative rate method (RR/DF/MS). At 298 ± 2 K, the rate constant for the Cl + CH₃CH₂OD reaction was determined using cyclohexane as a reference and found to be k₃ = (1.13 ± 0.21) × 10^?10 cm³ molecule^?1 s^?1. Mass spectral studies of the reaction products resulted in yields greater than 97% for the combined hydrogen abstraction at the α and β sites (3a + 3b) and less than 3% at the hydroxyl site (3c). As a calibration of the apparatus and the RR/DF/MS technique, the rate constant of the Cl + CH₃CH₂OH reaction was also determined using cyclohexane as the reference, and a value of k₂ = (1.05 ± 0.07) × 10^?10 cm³ molecule^?1 s^?1 was obtained at 298 ± 2 K, which was in excellent agreement with the value given in current literature. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 584–590, 2004     

Rate constants for the gas-phase reactions of alkanes with Cl atoms at 296 ± 2 K

Rate constants for the gas-phase reactions of the Cl atom with a series of alkanes have been determined at 296 ± 2 K using a relative rate method. Using a rate constant for the Cl atom reaction with n-butane of 1.94 × 10^?10 cm³ molecule^?1 s^?1, the rate constants obtained (in units of 10^?11 cm³ molecule^?1 s^?1) were: 2-methylpentane, 25.0 ± 0.8; 3-methylpentane, 24.8 ± 0.6; cyclohexane, 30.8 ± 1.2; cyclohexane-d₁₂, 25.6 ± 0.8; 2,4-dimethylpentane, 25.6 ± 1.2; 2,2,3-trimethylbutane, 17.9 ± 0.7; methylcyclohexane, 34.7 ± 1.2; n-octane, 40.5 ± 1.2; 2,2,4-trimethylpentane, 23.1 ± 0.8; 2,2,3,3-tetramethylbutane, 15.6 ± 0.9; n-nonane, 42.9 ± 1.2; n-decane, 48.7 ± 1.8; and cis-bicyclo[4.4.0]decane, 43.1 ± 0.8, where the indicated errors are two least-squares standard deviations and do not include the uncertainties in the n-butane rate constant. These data have been combined with rate constants obtained previously for ten C₂? C₇ alkanes and this entire data set has been used to develop an estimation method allowing the room temperature rate constants for the reactions of the Cl atom with alkanes to be calculated. © 1995 John Wiley & Sons, Inc.     

Kinetic study of the gas‐phase reaction of hydroxyl radical with CF3CH2OCH2CF3 using the laser photolysis–laser induced fluorescence method

The laser photolysis‐laser‐induced fluorescence method was used for measuring the kinetic parameters of the reaction of OH radicals with CF₃CH₂OCH₂CF₃ (2,2,2‐trifluoroethyl ether), in the temperature range of 298–365 K. The bimolecular rate coefficient at 298 K, k_II(298), was measured to be (1.47 ± 0.03) × 10^?13 cm³ molecule^?1 s^?1, and the temperature dependence of k_II was determined to be (4.5 ± 0.8) × 10^?12exp [?(1030 ± 60)/T] cm³ molecule^?1 s^?1. The error quoted is 1σ of the linear regression of the respective plots. The rate coefficient at room temperature is very close to the average of the three previous measurements, whereas the values of E_a/R and the A‐factor are higher than the two previously reported values. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 519–525, 2010     

Atmospheric reactions of chloroethenes with the OH radical

The kinetics and products of the homogeneous gas-phase reactions of the OH radical with the chloroethenes were investigated at 298 ± 2 K and atmospheric pressure. Using a relative rate technique and ethane as a scavenger for the chlorine atoms produced in these OH radical reactions, rate constants (in units of 10^?12 cm³ molecule^?1s^?1) of 8.11 ± 0.24, 2.38 ± 0.14, and 1.80 ± 0.03 were obtained for 1,1-dichloroethene, cis-1, 2-dichloroethene and trans-1,2-dichloroethene, respectively. Under these conditions, the major products observed by long pathlength FT-IR absorption spectroscopy were HCHO and HC(O)Cl from vinyl chloride; HC(O)Cl from cis- and trans-1,2-dichloroethene; HCHO and COCl₂ from 1,1-dichloroethene; HC(O)Cl and COCl₂ from trichloroethene; and COCl₂ from tetrachloroethene. In the absence of a Cl atom scavenger, significant yields of the chloroacetyl chlorides, CH_xCl_3?xC(O)Cl, were observed from 1,1-dichloro-, trichloro- and tetrachloroethene, indicating that these products resulted from reactions involving chlorine atoms. The yields of all of these products are reported and the mechanisms of these gas-phase reactions discussed. In addition, OH radical reaction rate constants were redetermined, in the presence of a Cl atom scavenger, for cis- and trans-1,3-dichloropropene and 3-chloro-2-chloromethyl-1-propene, being (in units of 10^?12 cm³ molecule^?1 s^?1) 8.45 ± 0.41, 14.4 ± 0.8, and 33.5 ± 3.0, respectively.