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     

Kinetics of the gas phase reaction of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure

Using a relative rate technique, rate constants have been determined for the gas phase reactions of Cl atoms with a series of organics at 296 ± 2 K and atmospheric pressure of air. Using a rate constant of 1.97 × 10^?10 cm³ molecule^?1 s^?1 for the reaction of Cl atoms with n-butane, the following rate constants (in units of 10^?11 cm³ molecule^?1 s^?1) were obtained: ethane, 6.38 ± 0.18; propane, 13.4 ± 0.5; isobutane, 13.7 ± 0.2; n-pentane, 25.2 ± 1.2; isopentane, 20.3 ± 0.8; neopentane, 11.0 ± 0.3; n-hexane, 30.3 ± 0.6; cyclohexane, 31.1 ± 1.4; 2,3-dimethylbutane, 20.7 ± 0.6; n-heptane, 34.1 ± 1.2; acetylene, 6.28 ± 0.18; ethene, 10.6 ± 0.3; propene, 24.4 ± 0.8; benzene, 1.5 ± 0.9; and toluene, 5.89 ± 0.36. These data are compared and discussed with the available literature values.     

Gas‐phase rate coefficients for a series of alkyl cyclohexanes with OH radicals and Cl atoms

The rate coefficients of the reactions of OH radicals and Cl atoms with three alkylcyclohexanes compounds, methylcyclohexane (MCH), trans‐1,4‐dimethylcyclohexane (DCH), and ethylcyclohexane (ECH) have been investigated at (293 ± 1) K and 1000 mbar of air using relative rate methods. A majority of the experiments were performed in the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC), a stainless steel chamber using in situ FTIR analysis and online gas chromatography with flame ionization detection (GC‐FID) detection to monitor the decay of the alkylcyclohexanes and the reference compounds. The studies were undertaken to provide kinetic data for calibrations of radical detection techniques in HIRAC. The following rate coefficients (in cm³ molecule⁻¹ s⁻¹) were obtained for Cl reactions: k_(Cl+MCH) = (3.51 ± 0.37) × 10^–10, k_(Cl+DCH) = (3.63 ± 0.38) × 10⁻¹⁰, k_(Cl+ECH) = (3.88 ± 0.41) × 10⁻¹⁰, and for the reactions with OH radicals: k_(OH+MCH) = (9.5 ± 1.3) × 10^–12, k_(OH+DCH) = (12.1 ± 2.2) × 10⁻¹², k_(OH+ECH) = (11.8 ± 2.0) × 10⁻¹². Errors are a combination of statistical errors in the relative rate ratio (2σ) and the error in the reference rate coefficient. Checks for possible systematic errors were made by the use of two reference compounds, two different measurement techniques, and also three different sources of OH were employed in this study: photolysis of CH₃ONO with black lamps, photolysis of H₂O₂ at 254 nm, and nonphotolytic trans‐2‐butene ozonolysis. For DCH, some direct laser flash photolysis studies were also undertaken, producing results in good agreement with the relative rate measurements. Additionally, temperature‐dependent rate coefficient investigations were performed for the reaction of methylcyclohexane with the OH radical over the range 273‐343 K using the relative rate method; the resulting recommended Arrhenius expression is k_{(OH + MCH)} = (1.85 ± 0.27) × 10^–11 exp((–1.62 ± 0.16) kJ mol⁻¹/RT) cm³ molecule⁻¹ s⁻¹. The kinetic data are discussed in terms of OH and Cl reactivity trends, and comparisons are made with the existing literature values and with rate coefficients from structure‐activity relationship methods. This is the first study on the rate coefficient determination of the reaction of ECH with OH radicals and chlorine atoms, respectively.     

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     

Study of the reactions of OH with HCl,HBr, and HI between 298 K and 460 K

The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be k_HCl(298 K) = (7.9 ± 1.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ with a weak positive temperature dependence, k_HBr (298-460 K) = (1.04 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_HI(298 K) = (3.0 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The homogeneous nature of these reactions has been experimentally tested.     

Absolute rate constants of the reactions of OH with cyclohexane and ethane at 296 ± 2 K by the discharge flow method

We present absolute measurements of the rate constant for the reactions of OH with cyclohexane: k₁=(8.6±0.8) × 10⁻¹² cm³ molecule⁻¹s⁻¹ and with ethane: k₃= (2.74±0.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹, both measured at room temperature by discharge flow resonance fluorescence. Our result for k₁ is above the average of two previously published measurements, but is in agreement with the preferred values of two recent reviews, as deduced from either relative measurements or theoretical correlations.     

A kinetic study of chlorine radical reactions with ketones by laser photolysis technique

Rate coefficients for reactions between Cl radicals and four ketones were determined at 294 ± 1 K with a relative rate method using a laser photolysis technique. The experiments were conducted in synthetic air in a flow system at atmospheric pressure. A mixture of Cl₂/ClONO₂ was photolyzed and the formation of NO₃ through the reaction Cl + ClONO₂ → Cl₂ + NO₃ was measured with and without ketones in the reaction mixture. The NO₃ radical concentration was measured by optical absorption using a diode laser as the light source. The rate coefficients for the Cl-ketone reactions could then be evaluated. The following rate coefficients were obtained (in units of cm³ molecule⁻¹ s⁻¹): cyclohexanone (7.00 ± 1.15) × 10⁻¹¹; cyclopentanone (4.76 ± 0.33) × 10⁻¹¹; acetone (1.69 ± 0.32) × 10⁻¹²; and 2,3-butanedione (7.62 ± 1.66) × 10⁻¹³. The accuracy of the method employed was tested by using the well-studied reaction between Cl and methane and a rate coefficient of (9.37 ± 1.04) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ was obtained, which is in good agreement with previous work. The errors are at the 95% confidence level. The results in this work indicate that a carbonyl group in a ketone lowers the reactivity towards α-hydrogen abstraction by Cl radicals, compared to the corresponding Cl-alkane reactions. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 195–201, 1997.     

Room temperature rate constants for the reaction of OH with selected chlorinated and oxygenated hydrocarbons

A study was conducted to measure the hydroxyl radical rate constants using a relative rate procedure in which the photolysis of methyl nitrite was the source of OH. During the course of this study, the OH rate constant was measured for a number of chlorinated solvents for which measurements have not previously been reported or for which there are few reliable measurements. Room temperature OH rate constants are presented for six chlorinated hydrocarbons (allyl chloride, benzyl chloride, chlorobenzene, epichlorohydrin, trichloroethylene, and vinylidene chloride) and four oxygenated hydrocarbons (acrolein, methacrolein, methyl ethyl ketone, and propylene oxide). Also included are OH rate constants for alkanes (ethane, propane, isobutane, and cyclohexane), alkenes (trans?2-butene and isoprene), and aromatic hydrocarbons (benzene, toluene, o^?, m^?, and p-xylene). Rate constants for compounds not previously reported include vinylidene chloride (1.49 ± 0.21 × 10^?11 cm³ molecule^?1 s^?1) and benzyl chloride (2.96 ± 0.15 × 10^?12 cm³ molecule^?1 s^?1). The analysis for chlorinated hydrocarbons included a correction for possible chlorine atom reactions.     

Absolute rate constants for the gas-phase reaction of OH radicals with cyclohexane and ethane at 295 K

The absolute rate constants for the gas-phase H-atom abstraction by hydroxyl radicals from cyclohexane and ethane have been determined at room temperature. OH radicals were produced by pulse radiolysis of an H₂O-Ar mixture, and the decay of OH was followed by monitoring the transient light absorption around 309 nm. The rate constants were found to be k = (5.24±0.36) × 10⁻¹² and (2.98±0.21) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ for cyclohexane and ethane, res- pectively. These results are compared with literature data.     

Temperature-dependent rate constants for the reactions of chlorine atom with methanol and Br2

Kinetics of the reaction of Cl atoms with methanol has been investigated at 2 Torr total pressure of helium and over a wide temperature range 225-950 K, using a discharge flow reactor combined with an electron impact ionization quadrupole mass spectrometer. The rate constant of the reaction Cl + CH₃OH → products (1) was determined using both absolute measurements under pseudo-first order conditions, monitoring the kinetics of Cl-atom consumption in excess of methanol and relative rate method, k₁ = (5.1 ± 0.8) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and was found to be temperature independent over the range T = 225-950 K. The rate constant of the reaction Cl + Br₂ → BrCl + Br (3) was measured in an absolute way monitoring Cl-atom decays in excess of Br₂: k₃ = 1.64 × 10⁻¹⁰ exp(34/T) cm³ molecule⁻¹ s⁻¹ at T = 225-960 K (with conservative 15% uncertainty). The experimental data for k₃ can also be adequately represented by the temperature independent value of k₃ = (1.8 ± 0.3) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. The kinetic data from the present study are compared with previous measurements.     

Kinetics of the reactions of hydroxyl radicals (OH) and of chlorine atoms (Cl) with methylethylether over the temperature range 274–345 K

The rate constants for the gas-phase reactions between methylethylether and hydroxyl radicals (OH) and methylethylether and chlorine atoms (Cl) have been determined over the temperature range 274–345 K using a relative rate technique. In this range the rate constants vary little with temperature and average values of k_MEE+OH = (6.60_−2.62^+3.88) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k_MEE+Cl= (34.9 ± 6.7) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were obtained. The atmospheric lifetimes of methylethylether have been estimated with respect to removal by OH radicals and Cl atoms to be ca. 2 days and ca. 30–40 days, respectively. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 231–236, 1997.     

Kinetics of the gas-phase reactions of Cl atoms with chloroethenes at 298 ± 2 K and atmospheric pressure

Using a relative rate technique, rate constants have been determined for the gas-phase reactions of Cl atoms with the cholorethenes and ethane at 298 ± 2 K and 735 torr total pressure of air. Using a rate constant of 1.97 × 10^?10 cm³ molecule^?1 s^?1 for the reaction of Cl atoms with n-butane, the following rate constants (in units of 10^?11 cm³ molecule^?1 s^?1) were obtained: vinyl chloride, 12.7 ± 0.2; 1,1-dichloroethene, 14.0 ± 0.2; cis-1,2-dichloroethene, 9.65 ± 0.10; trans-1,2-dichloroethene, 9.58 ± 0.18; trichloroethene, 8.08 ± 0.10; tetrachloroethene, 4.13 ± 0.23; and ethane, 6.17 ± 0.08 (where the indicated error limits do not include the uncertainties in the rate constant for n-butane). A small amount of cis-trans isomerization was observed for the reactions involving the cis- and trans-1,2-dichloroethenes. These data are compared and discussed with the available literature data.     

Kinetics and mechanism of the reaction of propylene oxide with chlorine atoms and hydroxy radicals

The kinetics and mechanism of gas‐phase propylene oxide (PPO) reactions were studied in a 142‐L reaction chamber by long‐path Fourier transform infrared spectroscopy at atmospheric pressure and 298 K. Rate coefficients for the reaction of PPO with ozone (O₃), chlorine atoms (Cl), and hydroxyl radicals (OH) were measured using the relative rate technique. Product yields of acetic acid, acetic formic anhydride, formic acid, and carbon monoxide were determined for the following reactions: PPO with Cl both in the presence and absence of NO, PPO with OH and NO, methyl acetate with Cl both in the presence and absence of NO, and ethyl formate with Cl both in the presence and absence of NO. The measured rate coefficients for PPO with O₃, Cl, and OH are <3.5 × 10^?21 cm³ molecule^?1 s^?1, (3.0 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1, and (3.0 ± 1.0) × 10^?13 cm³ molecule^?1 s^?1, respectively. The carbon balance for the products measured ranged from 10% (for OH + PPO) to 100% (for Cl + methyl acetate in the absence of NO). The mechanistic and atmospheric implications of these measurements are discussed. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 507–521, 2011     

Determination of the rate constants for the gas-phase reactions of methyl butenol with OH radicals,ozone, NO3 radicals,and Cl atoms

Using a relative rate method, rate constants for the gas-phase reactions of 2-methyl-3-buten-2-ol (MBO) with OH radicals, ozone, NO₃ radicals, and Cl atoms have been investigated using FTIR. The measured values for MBO at 298±2 K and 740±5 torr total pressure are: k_OH=(3.9±1.2)×10⁻¹¹ cm³ molecule⁻¹ s⁻¹, k_O3=(8.6±2.9)×10⁻¹⁸ cm³ molecule⁻¹ s⁻¹, k=(8.6±2.9)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹, and k_Cl=(4.7±1.0)×10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Atmospheric lifetimes have been estimated with respect to the reactions with OH, O₃, NO₃, and Cl. The atmospheric relevance of this compound as a precursor for acetone is, also, briefly discussed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 589–594, 1998     

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     

A kinetics study of the reaction of Cl with NO2

The third order rate coefficients for the addition reaction of Cl with NO₂, Cl + NO₂ + M → ClNO₂ (ClONO) + M; k₁, were measured to be k₁(He) = (7.5 ± 1.1) × 10^?31 cm⁶ molecule^?2 s^?1 and k₁(N₂) = (16.6 ± 3.0) × 10^?31 cm⁶ molecule^?2 s^?1 at 298 K using the flash photolysis-resonance fluorescence method. The pressure range of the study was 15 to 500 torr He and 19 to 200 torr N₂. The temperature dependence of the third order rate coefficients were also measured between 240 and 350 K. The 298 K results are compared with those from previous low pressure studies.     

Gas phase rate coefficients and activation energies for the reaction of butanal and 2‐methyl‐propanal with nitrate radicals

Rate coefficients have been determined for the reaction of butanal and 2‐methyl‐propanal with NO₃ using relative and absolute methods. The relative measurements were accomplished by using a static reactor with long‐path FTIR spectroscopy as the analytical tool. The absolute measurements were made using fast‐flow–discharge technique with detection of NO₃ by optical absorption. The resulting average coefficients from the relative rate experiments were k = (1.0 ± 0.1) × 10⁻¹⁴ and k = (1.2 ± 0.2) × 10⁻¹⁴ (cm³ molecule⁻¹ s⁻¹) for butanal and 2‐methyl‐propanal, respectively. The results from the absolute measurements indicated secondary reactions involving NO₃ radicals and the primary formed acyl radicals. The prospect of secondary reactions was investigated by means of mathematical modeling. Calculations indicated that the unwanted NO₃ radical reactions could be suppressed by introducing molecular oxygen into the flow tube. The rate coefficients from the absolute rate experiments with oxygen added were and k = (1.2 ± 0.1) × 10⁻¹⁴ and = (0.9 ± 0.1) × 10⁻¹⁴ (cm³ molecule⁻¹ s⁻¹) for butanal and 2‐methyl‐propanal. The temperature dependence of the reactions was studied in the range between 263 and 364 K. Activation energies for the reactions were determined to 12 ± 2 kJ mole⁻¹ and 14 ± 1 kJ mole⁻¹ for butanal and 2‐methyl‐propanal, respectively. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 294–303, 2000     

Direct measurement of the C2H5C(O)O2 + NO reaction rate coefficient using chemical ionization mass spectrometry

The rate coefficient for the reaction of the peroxypropionyl radical (C₂H₅C(O)O₂) with NO was measured with a laminar flow reactor over the temperature range 226–406 K. The C₂H₅C(O)O₂ reactant was monitored with chemical ionization mass spectrometry. The measured rate coefficients are k(T) = (6.7 ± 1.7) × 10⁻¹² exp{(340 ± 80)/T} cm³ molecule⁻¹ s⁻¹ and k(298 K) = (2.1 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. Our results are comparable to recommended rate coefficients for the analogous CH₃C(O)O₂ + NO reaction. Heterogeneous effects, pressure dependence, and concentration gradients inside the flow reactor are examined. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet: 31: 221–228, 1999     

Rates of reaction between the nitrate radical and some unsaturated alcohols

Rate coefficients for nitrate radical gas-phase reactions with prop-2-en-l-ol (allyl alcohol), but-1-en-3-ol, and 2-methylbut-3-en-2-ol have been determined. Both absolute (fast flow discharge with diode laser detection of NO₃) and relative (batch reactor and FTIR spectroscopy) rate techniques were used to measure the rate coefficients. The rate coefficients at 294 K are: (1.3 ± 0.2) × 10⁻¹⁴, (1.2 ± 0.3) × 10 ⁻¹⁴, and (2.1 ± 0.3) × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹ for prop-2-en-1-ol, but-1-en-3-ol, and 2-methylbut-3-en-2-ol, respectively. The activation energy for reaction of NO₃ with prop-2-en-1-ol was determined to 2.8 ± 2.5 kJ mol⁻¹ in the temperature range between 273 and 363 K. The atmospheric importance of unsaturated alcohols and structure-reactivity considerations are also discussed. © 1996 John Wiley & Sons, Inc.     

Gas phase reaction of Cl atoms with a series of oxygenated organic species at 295 K

The relative rate technique has been used to determine the rate constants for the reaction of chlorine atoms with a series of oxygenated organic species. Experiments were performed at 295 ± 2 K and atmospheric pressure of synthetic air or nitrogen. The decay rates of the organic species were measured relative to that of ethane or n-butane. Using rate constants of 5.7 × 10^?11 cm³ molecule^?1 s^?1, and 2.25 × 10^?10 cm³ molecule^?1 s^?1 for the reaction of Cl with ethane and n-butane respectively the following rate constants were derived, in units of 10^?11 cm³ molecule^?1 s^?1: propane, (16.0 ± 0.4);i-butane, (15.1 ± 0.9) n-pentane, (31.0 ± 1.6); n-hexane, (34.5 ± 2.3); cyclohexane, (36.1 ± 1.5); methanol, (4.57 ± 0.40); ethanol, (8.45 ± 0.91); n-propanol, (14.4 ± 1.2); t-butylalcohol, (3.26 ± 0.19); acetaldehyde, (8.45 ± 0.79); propionaldehyde, (11.3 ± 0.9); dimethylether, (20.5 ± 0.8); diethylether, (35.6 ± 2.8); and methyl-t-butylether, (16.6 ± 1.2). Quoted errors represent 2σ, and do not include any errors due to uncertainties in the rate constants used to place our relative measurements on an absolute basis. The results are discussed with respect to the mechanisms of these reactions and to previous literature data.