Rate coefficients for the reactions CH3 + Br2 (224–358 K), CH3CO + Br2 (228 and 298 K), and Cl + Br2 (228 and 298 K)

Rate coefficients for the reactions of CH₃ + Br₂ (k₂), CH₃CO + Br₂ (k₃), and Cl + Br₂ (k₅) were measured using the laser‐pulsed photolysis method combined with detection of the product Br atoms using resonance fluorescence. For the reactions involving organic radicals, the rate coefficients were observed to increase with decreasing temperature and within the temperature range explored, were adequately described by Arrhenius‐like expressions: k₂ (224–358 K) = 1.83 × 10^?11 exp(252/T) and k₃ (228–298 K) = 2.92 × 10^?11 exp(361/T) cm³ molecule^?1 s^?1. The total, temperature‐independent uncertainty for each reaction (including possible systematic errors in Br₂ concentration measurement) was estimated as ～7% for k₂ and 10% for k₃. Accurate data on k₅ was obtained at 298 K, with a value of 1.88 × 10^?10 cm³ molecule^?1 s^?1 obtained (with an associated error of 6%). A limited data set at 228 K suggests that k₅ is, within experimental uncertainty, independent of temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 575–585, 2010     

Rate coefficients and mechanisms of the reaction of cl‐atoms with a series of unsaturated hydrocarbons under atmospheric conditions

Rate coefficients and/or mechanistic information are provided for the reaction of Cl‐atoms with a number of unsaturated species, including isoprene, methacrolein ( MACR ), methyl vinyl ketone ( MVK ), 1,3‐butadiene, trans‐2‐butene, and 1‐butene. The following Cl‐atom rate coefficients were obtained at 298 K near 1 atm total pressure: k(isoprene) = (4.3 ± 0.6) × 10^?10cm³ molecule^?1 s^?1 (independent of pressure from 6.2 to 760 Torr); k( MVK ) = (2.2 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1; k( MACR ) = (2.4 ± 0.3) × 10^?10 cm³ molecule^?1 s^?1; k(trans‐2‐butene) = (4.0 ± 0.5) × 10^?10 cm³ molecule^?1 s^?1; k(1‐butene) = (3.0 ± 0.4) × 10^?10 cm³ molecule^?1 s^?1. Products observed in the Cl‐atom‐initiated oxidation of the unsaturated species at 298 K in 1 atm air are as follows (with % molar yields in parentheses): CH₂O (9.5 ± 1.0%), HCOCl (5.1 ± 0.7%), and 1‐chloro‐3‐methyl‐3‐buten‐2‐one (CMBO, not quantified) from isoprene; chloroacetaldehyde (75 ± 8%), CO₂ (58 ± 5%), CH₂O (47 ± 7%), CH₃OH (8%), HCOCl (7 ± 1%), and peracetic acid (6%) from MVK ; CO (52 ± 4%), chloroacetone (42 ± 5%), CO₂ (23 ± 2%), CH₂O (18 ± 2%), and HCOCl (5%) from MACR ; CH₂O (7 ± 1%), HCOCl (3%), acrolein (≈3%), and 4‐chlorocrotonaldehyde (CCA, not quantified) from 1,3‐butadiene; CH₃CHO (22 ± 3%), CO₂ (13 ± 2%), 3‐chloro‐2‐butanone (13 ± 4%), CH₂O (7.6 ± 1.1%), and CH₃OH (1.8 ± 0.6%) from trans‐2‐butene; and chloroacetaldehyde (20 ± 3%), CH₂O (7 ± 1%), CO₂ (4 ± 1%), and HCOCl (4 ± 1%) from 1‐butene. Product yields from both trans‐2‐butene and 1‐butene were found to be O₂‐dependent. In the case of trans‐2‐butene, the observed O₂‐dependence is the result of a competition between unimolecular decomposition of the CH₃CH(Cl)? CH(O?)? CH₃ radical and its reaction with O₂, with k_decomp/k_O2 = (1.6 ± 0.4) × 10¹⁹ molecule cm^?3. The activation energy for decomposition is estimated at 11.5 ± 1.5 kcal mol^?1. The variation of the product yields with O₂ in the case of 1‐butene results from similar competitive reaction pathways for the two β‐chlorobutoxy radicals involved in the oxidation, ClCH₂CH(O?)CH₂CH₃ and ?OCH₂CHClCH₂CH₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 334–353, 2003     

Rate coefficients for the reactions of chlorine atoms with methanol and acetaldehyde

Rate coefficients have been measured for the reactions of Cl atoms with methanol (k₁) and acetaldehyde (k₂) using both absolute (laser photolysis with resonance fluorescence) and relative rate methods at 295 ± 2 K. The measured rate coefficients were (units of 10⁻¹¹ cm³ molecule⁻¹ s⁻¹): absolute method, k₁ = (5.1 ± 0.4), k₂ = (7.3 ± 0.7); relative method k₁ = (5.6 ± 0.6), k₂ = (8.4 ± 1.0). Based on a critical evaluation of the literature data, the following rate coefficients are recommended: k₁ = (5.4 ± 0.9) × 10⁻¹¹ and k₂ = (7.8 ± 1.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ (95% confidence limits). The results significantly improve the confidence in the database for reactions of Cl atoms with these oxygenated organics. Rate coefficients were also measured for the reactions of Cl₂ with CH₂OH, k₅ = (2.9 ± 0.6) × 10⁻¹¹ and CH₃CO, k₆ = (4.3 ± 1.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, by observing the regeneration of Cl atoms in the absence of O₂. Based on these results and those from a previous relative rate study, the rate coefficient for CH₃CO + O₂ at the high pressure limit is estimated to be (5.7 ± 1.9) × 10⁻¹² cm³ molecule⁻¹ s⁻¹. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 776–784, 1999     

Rate coefficients for the reactions of OH with n‐propanol and iso‐propanol between 237 and 376 K

The rate coefficients for the reaction OH + CH₃CH₂CH₂OH → products (k₁) and OH + CH₃CH(OH)CH₃ → products (k₂) were measured by the pulsed‐laser photolysis–laser‐induced fluorescence technique between 237 and 376 K. Arrhenius expressions for k₁ and k₂ are as follows: k₁ = (6.2 ± 0.8) × 10^?12 exp[?(10 ± 30)/T] cm³ molecule^?1 s^?1, with k₁(298 K) = (5.90 ± 0.56) × 10^?12 cm³ molecule^?1 s^?1, and k₂ = (3.2 ± 0.3) × 10^?12 exp[(150 ± 20)/T] cm³ molecule^?1 s^?1, with k₂(298) = (5.22 ± 0.46) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainties are at the 95% confidence level and include estimated systematic errors. The results are compared with those from previous measurements and rate coefficient expressions for atmospheric modeling are recommended. The absorption cross sections for n‐propanol and iso‐propanol at 184.9 nm were measured to be (8.89 ± 0.44) × 10^?19 and (1.90 ± 0.10) × 10^?18 cm² molecule^?1, respectively. The atmospheric implications of the degradation of n‐propanol and iso‐propanol are discussed. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 10–24, 2010     

Kinetic parameters for the reaction of hydroxyl radical with CH3OCH2F (HFE‐161) in the temperature range of 200–400 K: Transition state theory and Ab initio calculations

Rate coefficients for the reaction of the hydroxyl radical with CH₃OCH₂F (HFE‐161) were computed using transition state theory coupled with ab initio methods, viz., MP2, G3MP2, and G3B3 theories in the temperature range of 200–400 K. Structures of the reactants and transition states (TSs) were optimized at MP2(FULL) and B3LYP level of theories with 6‐31G* and 6‐311++G** basis sets. The potential energy surface was scanned at both the level of theories. Five different TSs were identified for each rotamer. Calculations of Intrinsic reaction coordinates were performed to confirm the existence of all the TSs. The kinetic parameters due to all different TSs are reported in this article. The rate coefficients for the title reaction were computed to be k = (9 ± 1.08) × 10^?13 exp [?(1,713 ± 33)/T] cm³ molecule^?1 s^?1 at MP2, k = (7.36 ± 0.42) × 10^?13 exp [?(198 ± 16)/T] cm³ molecule^?1 s^?1 at G3MP2 and k = (5.36 ± 1.57) × 10^?13 exp [?(412 ± 81)/T] cm³ molecule^?1 s^?1 at G3B3 theories. The atmospheric lifetimes of CH₃OCH₂F at MP2, G3MP2, and G3B3 level of theories were estimated to be 20, 0.1, and 0.3 years, respectively. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Kinetics of the gas‐phase reactions of chlorine atoms with CH2F2, CH3CCl3, and CF3CFH2 over the temperature range 253–553 K

Relative rate techniques were used to study the title reactions in 930–1200 mbar of N₂ diluent. The reaction rate coefficients measured in the present work are summarized by the expressions k(Cl + CH₂F₂) = 1.19 × 10^?17 T² exp(?1023/T) cm³ molecule^?1 s^?1 (253–553 K), k(Cl + CH₃CCl₃) = 2.41 × 10^?12 exp(?1630/T) cm³ molecule^?1 s^?1 (253–313 K), and k(Cl + CF₃CFH₂) = 1.27 × 10^?12 exp(?2019/T) cm³ molecule^?1 s^?1 (253–313 K). Results are discussed with respect to the literature data. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 401–406, 2009     

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.     

Rate coefficients for the O(3P) + Cl2O gas‐phase reaction between 230 and 357 K

Rate coefficients, k, for the gas‐phase reaction of O(³P) atoms with Cl₂O (dichlorine monoxide) over a range of temperatures (230–357 K) at pressures between 12 and 32 Torr (N₂) are reported. Rate coefficients were measured under pseudo‐first‐order conditions in O(³P) using pulsed laser photolysis to produce O(³P) atoms and atomic resonance fluorescence to detect its temporal profile. The rate coefficient temperature dependence is given by the Arrhenius expression k(T) = (1.51 ± 0.20) × 10^?11 exp[?(477 ± 30)/T] cm³ molecule^?1 s^?1, and k(296 K) was measured to be (2.93 ± 0.30) × 10^?12 cm³ molecule^?1 s^?1. The quoted uncertainty limits are at the 2σ (95% confidence) level and include estimated systematic errors. The rate coefficients determined in the present study, under conditions that minimized secondary losses of O(³P), are compared with previous results from other laboratories and the discrepancies are discussed. © 2011 Wiley Peiodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 43: 312–321, 2011     

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     

Rate coefficients and ClO radical yields in the reaction of O(1D) with CClF2CCl2F,CCl3CF3, CClF2CClF2, and CCl2FCF3

Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(¹D) with CClF₂CCl₂F (CFC‐113) (k₂), CCl₃CF₃ (CFC‐113a) (k₃), CClF₂CClF₂ (CFC‐114) (k₄), and CCl₂FCF₃ (CFC‐114a) (k₅) at 296 K are reported. Rate coefficients for the loss of O(¹D) were measured using a competitive reaction technique, with n‐butane (n‐C₄H₁₀) as the reference reactant, employing pulsed laser photolysis production of O(¹D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k₂ = (2.33 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.61 ± 0.40) × 10^?10 cm³ molecule^?1 s^?1, k₄ = (1.42 ± 0.25) × 10^?10 cm³ molecule^?1 s^?1, and k₅ = (1.62 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America

Int J Chem Kinet 43: 393–401, 2011     

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 the reactions of C2H5, n‐C3H7, and n‐C4H9 radicals with Cl2 at the temperature range 190–360 K

The kinetics of the C₂H₅ + Cl₂, n‐C₃H₇ + Cl₂, and n‐C₄H₉ + Cl₂ reactions has been studied at temperatures between 190 and 360 K using laser photolysis/photoionization mass spectrometry. Decays of radical concentrations have been monitored in time‐resolved measurements to obtain reaction rate coefficients under pseudo‐first‐order conditions. The bimolecular rate coefficients of all three reactions are independent of the helium bath gas pressure within the experimental range (0.5–5 Torr) and are found to depend on the temperature as follows (ranges are given in parenthesis): k(C₂H₅ + Cl₂) = (1.45 ± 0.04) × 10^?11 (T/300 K)^{?1.73 ± 0.09} cm³ molecule^?1 s^?1 (190–359 K), k(n‐C₃H₇ + Cl₂) = (1.88 ± 0.06) × 10^?11 (T/300 K)^{?1.57 ± 0.14} cm³ molecule^?1 s^?1 (204–363 K), and k(n‐C₄H₉ + Cl₂) = (2.21 ± 0.07) × 10^?11 (T/300 K)^{?2.38 ± 0.14} cm³ molecule^?1 s^?1 (202–359 K), with the uncertainties given as one‐standard deviations. Estimated overall uncertainties in the measured bimolecular reaction rate coefficients are ±20%. Current results are generally in good agreement with previous experiments. However, one former measurement for the bimolecular rate coefficient of C₂H₅ + Cl₂ reaction, derived at 298 K using the very low pressure reactor method, is significantly lower than obtained in this work and in previous determinations. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 614–619, 2007     

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     

Rate coefficients for the OH + acetaldehyde (CH3CHO) reaction between 204 and 373 K

The rate coefficient, k₁, for the gas‐phase reaction OH + CH₃CHO (acetaldehyde) → products, was measured over the temperature range 204–373 K using pulsed laser photolytic production of OH coupled with its detection via laser‐induced fluorescence. The CH₃CHO concentration was measured using Fourier transform infrared spectroscopy, UV absorption at 184.9 nm and gas flow rates. The room temperature rate coefficient and Arrhenius expression obtained are k₁(296 K) = (1.52 ± 0.15) × 10^?11 cm³ molecule^?1 s^?1 and k₁(T) = (5.32 ± 0.55) × 10^?12 exp[(315 ± 40)/T] cm³ molecule^?1 s^?1. The rate coefficient for the reaction OH (ν = 1) + CH₃CHO, k₇(T) (where k₇ is the rate coefficient for the overall removal of OH (ν = 1)), was determined over the temperature range 204–296 K and is given by k₇(T) = (3.5 ± 1.4) × 10^?12 exp[(500 ± 90)/T], where k₇(296 K) = (1.9 ± 0.6) × 10^?11 cm³ molecule^?1 s^?1. The quoted uncertainties are 2σ (95% confidence level). The preexponential term and the room temperature rate coefficient include estimated systematic errors. k₇ is slightly larger than k₁ over the range of temperatures included in this study. The results from this study were found to be in good agreement with previously reported values of k₁(T) for temperatures <298 K. An expression for k₁(T), suitable for use in atmospheric models, in the NASA/JPL and IUPAC format, was determined by combining the present results with previously reported values and was found to be k₁(298 K) = 1.5 × 10^?11 cm³ molecule^?1 s^?1, f(298 K) = 1.1, E/R = 340 K, and Δ E/R (or g) = 20 K over the temperature range relevant to the atmosphere. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 635–646, 2008     

Temperature dependence of the rate coefficients for the reaction of chlorine atoms with chloromethanes

Rate coefficients for the reaction of Cl atoms with CH₃Cl (k₁), CH₂Cl₂ (k₂), and CHCl₃ (k₃) have been determined over the temperature range 222–298 K using standard relative rate techniques. These data, when combined with evaluated data from previous studies, lead to the following Arrhenius expressions (all in units of cm³ molecule⁻¹ s⁻¹): k₁ = (2.8 ± 0.3) × 10⁻¹¹ exp(−1200 ± 150/T); k₂ = (1.5 ± 0.2) × 10⁻¹¹ exp(−1100 ± 150/T); k₃ = (0.48 ± 0.05) × 10⁻¹¹ exp(−1050 ± 150/T). Values for k₁ are in substantial agreement with previous measurements. However, while the room temperature values for k₂ and k₃ agree with most previous data, the activation energies for these rate coefficients are substantially lower than previously recommended values. In addition, the mechanism of the oxidation of CH₂Cl₂ has been studied. The dominant fate of the CHCl₂O radical is decomposition via Cl‐atom elimination, even at the lowest temperatures studied in this work (218 K). However, a small fraction of the CHCl₂O radicals are shown to react with O₂ at low temperatures. Using an estimated value for the rate coefficient of the reaction of CHCl₂O with O₂ (1 × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹), the decomposition rate coefficient for CHCl₂O is found to be about 4 × 10⁶ s⁻¹ at 218 K, with the barrier to its decomposition estimated at 6 kcal/mole. As part of this work, the rate coefficient for Cl atoms with HCOCl was also been determined, k₇ = 1.4 × 10⁻¹¹ exp(−885/T) cm³ molecule⁻¹ s⁻¹, in agreement with previous determinations. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 515–524, 1999     

Rate coefficients for the reaction of OH with Cl2, Br2, and I2 from 235 to 354 K

Rate coefficients for the reaction of OH with Cl₂, (k₁), Br₂, (k₂) and I₂, (k₃), were measured under pseudo‐first‐order conditions in OH. OH was produced by pulsed laser photolysis of H₂O₂ (or HNO₃) and its temporal profile was monitored by laser‐induced fluorescence. The measured rate coefficients for k₁ (231–354 K) and k₂ (235–357 K) are: k₁ (T) = (3.77 ± 1.02) × 10⁻¹² exp[−(1228 ± 140)/T] cm³ molecule⁻¹ s⁻¹ k₂ (T) = (1.98 ± 0.51) × 10⁻¹¹ exp[(238 ± 70)/T] cm³ molecule⁻¹ s⁻¹ k₃ was independent of temperature between 240 and 348 K with an average value of (2.10 ± 0.60) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The quoted uncertainties are 2σ (95% confidence limits, 1σ_A = Aσ_lnA) and include estimated systematic errors. Our measurements significantly im‐prove the accuracy of k₁. This is the first report of a slight negative temperature dependence for k₂ and of the temperature independence of k₃. © 1999 John Wiley & Sons, Inc.* Int J Chem Kinet 31: 417–424, 1999     

Rate constants for the elementary reactions between CN radicals and CH4, C2H6, C2H4, C3H6, and C2H2 in the range: 295 ⩽ T/K ⩽ 700

Pulsed laser photolysis, time-resolved laser-induced fluorescence experiments have been carried out on the reactions of CN radicals with CH₄, C₂H₆, C₂H₄, C₃H₆, and C₂H₂. They have yielded rate constants for these five reactions at temperatures between 295 and 700 K. The data for the reactions with methane and ethane have been combined with other recent results and fitted to modified Arrhenius expressions, k(T) = A′(298) (T/298)ⁿ exp(?θ/T), yielding: for CH₄, A′(298) = 7.0 × 10^?13 cm³ molecule^?1 s^?1, n = 2.3, and θ = ?16 K; and for C₂H₆, A′(298) = 5.6 × 10^?12 cm³ molecule^?1 s^?1, n = 1.8, and θ = ?500 K. The rate constants for the reactions with C₂H₄, C₃H₆, and C₂H₂ all decrease monotonically with temperature and have been fitted to expressions of the form, k(T) = k(298) (T/298)ⁿ with k(298) = 2.5 × 10^?10 cm³ molecule^?1 s^?1, n = ?0.24 for CN + C₂H₄; k(298) = 3.4 × 10^?10 cm³ molecule^?1 s^?1, n = ?0.19 for CN + C₃H₆; and k(298) = 2.9 × 10^?10 cm³ molecule^?1 s^?1, n = ?0.53 for CN + C₂H₂. These reactions almost certainly proceed via addition-elimination yielding an unsaturated cyanide and an H-atom. Our kinetic results for reactions of CN are compared with those for reactions of the same hydrocarbons with other simple free radical species. © John Wiley & Sons, Inc.     

FT‐IR kinetic and product study of the OH radical and Cl‐atom–initiated oxidation of dibasic esters

Using a relative kinetic technique, rate coefficients have been measured, at 296 ± 2 K and 740 Torr total pressure of synthetic air, for the gas‐phase reaction of OH radicals with the dibasic esters dimethyl succinate [CH₃OC(O)CH₂CH₂C(O)OCH₃], dimethyl glutarate [CH₃OC(O)CH₂CH₂CH₂C(O)OCH₃], and dimethyl adipate [CH₃OC(O)CH₂CH₂CH₂CH₂C(O)OCH₃]. The rate coefficients obtained were (in units of cm³ molecule^?1 s^?1): dimethyl succinate (1.89 ± 0.26) × 10^?12; dimethyl glutarate (2.13 ± 0.28) × 10^?12; and dimethyl adipate (3.64 ± 0.66) × 10^?12. Rate coefficients have been also measured for the reaction of chlorine atoms with the three dibasic esters; the rate coefficients obtained were (in units of cm³ molecule^?1 s^?1): dimethyl succinate (6.79 ± 0.93) × 10^?12; dimethyl glutarate (1.90 ± 0.33) × 10^?11; and dimethyl adipate (6.08 ± 0.86) × 10^?11. Dibasic esters are industrial solvents, and their increased use will lead to their possible release into the atmosphere, where they may contribute to the formation of photochemical air pollution in urban and regional areas. Consequently, the products formed from the oxidation of dimethyl succinate have been investigated in a 405‐L Pyrex glass reactor using Cl‐atom–initiated oxidation as a surrogate for the OH radical. The products observed using in situ Fourier transform infrared (FT‐IR) absorption spectroscopy and their fractional molar yields were: succinic formic anhydride (0.341 ± 0.068), monomethyl succinate (0.447 ± 0.111), carbon monoxide (0.307 ± 0.061), dimethyl oxaloacetate (0.176 ± 0.044), and methoxy formylperoxynitrate (0.032–0.084). These products account for 82.4 ± 16.4% C of the total reaction products. Although there are large uncertainties in the quantification of monomethyl succinate and dimethyl oxaloacetate, the product study allows the elucidation of an oxidation mechanism for dimethyl succinate. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 431–439, 2001     

Kinetics of the gas‐phase reactions of CHXCFX (X = H,F) with OH (253–328 K) and NO3 (298 K) radicals and O3 (236–308 K)

Rate constants for the reactions of OH and NO₃ radicals with CH₂?CHF (k₁ and k₄), CH₂?CF₂ (k₂ and k₅), and CHF?CF₂ (k₃ and k₆) were determined by means of a relative rate method. The rate constants for OH radical reactions at 253–328 K were k₁ = (1.20 ± 0.37) × 10^?12 exp[(410 ± 90)/T], k₂ = (1.51 ± 0.37) × 10^?12 exp[(190 ± 70)/T], and k₃ = (2.53 ± 0.60) × 10^?12 exp[(340 ± 70)/T] cm³ molecule^?1 s^?1. The rate constants for NO₃ radical reactions at 298 K were k₄ = (1.78 ± 0.12) × 10^?16 (CH₂?CHF), k₅ = (1.23 ± 0.02) × 10^?16 (CH₂?CF₂), and k₆ = (1.86 ± 0.09) × 10^?16 (CHF?CF₂) cm³ molecule^?1 s^?1. The rate constants for O₃ reactions with CH₂?CHF (k₇), CH₂?CF₂ (k₈), and CHF?CF₂ (k₉) were determined by means of an absolute rate method: k₇ = (1.52 ± 0.22) × 10^?15 exp[?(2280 ± 40)/T], k₈ = (4.91 ± 2.30) × 10^?16 exp[?(3360 ± 130)/T], and k₉ = (5.70 ± 4.04) × 10^?16 exp[?(2580 ± 200)/T] cm³ molecule^?1 s^?1 at 236–308 K. The errors reported are ±2 standard deviations and represent precision only. The tropospheric lifetimes of CH₂?CHF, CH₂?CF₂, and CHF?CF₂ with respect to reaction with OH radicals, NO₃ radicals, and O₃ were calculated to be 2.3, 4.4, and 1.6 days, respectively. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 619–628, 2010