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     

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.     

Kinetics of the gas‐phase reaction of CF3OC(O)H with OH radicals at 242–328 K

The rate constants, k₁, of the reaction of CF₃OC(O)H with OH radicals were measured by using a Fourier transform infrared spectroscopic technique in an 11.5‐dm³ reaction chamber at 242–328 K. 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 UV irradiation. With CF₃OCH₃ as a reference compound, k₁ at 298 K was (1.65 ± 0.13) × 10^?14 cm³ molecule^?1 s^?1. The temperature dependence of k₁ was determined as (2.33 ± 0.42) × 10^?12 exp[?(1480 ± 60)/T] cm³ molecule^?1 s^?1; possible systematic uncertainty could add an additional 20% to the k₁ values. The atmospheric lifetime of CF₃OC(O)H with respect to reaction with OH radicals was calculated to be 3.6 years. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 337–344 2004     

Rate constants of the reactions of OH radicals with cyclopropane and cyclobutane

The kinetics of the reactions of hydroxy radicals with cyclopropane and cyclobutane has been investigated in the temperature range of 298–492 K with laser flash photolysis/resonance fluorescence technique. The temperature dependence of the rate constants is given by k₁ = (1.17 ± 0.15) × 10^?16 T^3/2 exp[?(1037 ± 87) kcal mol^?1/RT] cm³ molecule^?1 s¹ and k₂ = (5.06 ± 0.57) × 10^?16 T^3/2 exp[?(228 ± 78) kcal mol^?1/RT] cm³ molecule^?1 s^?1 for the reactions OH + cyclopropane → products (1) and OH + cyclobutane → products (2), respectively. Kinetic data available for OH + cycloalkane reactions were analyzed in terms of structure-reactivity correlations involving kinetic and energetic parameters.     

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     

Kinetics of reactions of OBrO with NO,O3, OClO,and ClO at 240–350 K

Kinetics for the reactions of OBrO with NO, O₃, OClO, and ClO at 240–350 K were investigated using the technique of discharge flow coupled with mass spectrometry. The Arrhenius expression for the OBrO reaction with NO was determined to be k₁ = (2.37 ± 0.96) × 10^?13 exp[(607 ± 63)/T] cm³ molecule^?1 s^?1. The reactions of OBrO with O₃, OClO, and ClO are slow chemical processes at 240–350 K. Upper limit rate constants for the OBrO reactions with O₃, OClO, and ClO at 240–350 K were estimated to be k₂ < 5.0 × 10^?15 cm³ molecule^?1 s^?1, k₃ < 6.0 × 10^?14 cm³ molecule^?1 s^?1, and k₄ < 1.5 × 10^?13 cm³ molecule^?1 s^?1, respectively. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 430–437, 2002     

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.     

Gas‐Phase Reaction of Monomethylhydrazine with Ozone: Kinetics and OH Radical Formation

The gas‐phase reaction of monomethylhydrazine (CH₃NH? NH₂; MMH) with ozone was investigated in a flow tube at atmospheric pressure and a temperature of 295 ± 2 K using N₂/O₂ mixtures (3–30 vol% O₂) as the carrier gas. Proton transfer reaction–mass spectrometry (PTR‐MS) and long‐path FT‐IR spectroscopy served as the main analytical techniques. The kinetics of the title reaction was investigated with a relative rate technique yielding k_MMH+O3 = (4.3 ± 1.0) × 10^?15 cm³ molecule^?1 s^?1. Methyldiazene (CH₃N?NH; MeDia) has been identified as the main product in this reaction system as a result of PTR‐MS analysis. The reactivity of MeDia toward ozone was estimated relative to the reaction of MMH with ozone resulting in k_MeDia+O3 = (2.7 ± 1.6) × 10^?15 cm³ molecule^?1 s^?1. OH radicals were followed indirectly by phenol formation from the reaction of OH radicals with benzene. Increasing OH radical yields with increasing MMH conversion have been observed pointing to the importance of secondary processes for OH radical generation. Generally, the detected OH radical yields were definitely smaller than thought so far. The results of this study do not support the mechanism of OH radical formation from the reaction of MMH with ozone as proposed in the literature.     

Flash photolysis resonance fluorescence investigation of the reactions of OH radicals with OCS and CS2

Rate constants for the reaction of OH radicals with OCS and CS₂ have been determined at 296 K using the flash photolysis resonance fluorescence technique. The values derived from this study are k_{OH + OCS} = (5.66 ± 1.21) × 10^?14 cm³ molecule^?1 s^?1 and k_{OH + CS2} = (1.85 ± 0.34) × 10^?13 cm³ molecule^?1 s^?1, where the uncertainties are 95% confidence limits making allowance for possible systematic errors.     

Rate constants for the reaction of OH radicals with 2-methyl-2-butene over the temperature range 297–425 K

Absolute rate constants, k₂, for the reaction of OH radicals with 2-methyl-2-butene have been determined over the temperature range 297–425 K using a flash photolysis-resonance fluorescence technique. The Arrhenius expression obtained was k₂ = 3.6 × 10^?11 exp [(450 ± 400)/RT] cm³ molecule^?1 s^?1.     

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.     

Kinetics of the gas phase reaction of OH radicals with pyrrole and thiophene

Absolute rate constants for the gas phase reaction of OH radicals with pyrrole (k₁) and thiophene (k₂) have been measured over the temperature ranges 298–440 and 274–382 K, respectively, using the flash photolysis-resonance fluorescence technique. The rate constants obtained were independent of the total pressure of argon diluent over the range 25–100 torr andwere fit by the Arrhenius expressions and with rate constants at 298 ± 2 K of k₁ = (1.03 ± 0.06) × 10^?10 cm³ molecule^?1 s^?1 and k₂ = (8.9 ± 0.7) × 10^?12 cm³ molecule^?1 s^?1. [These errors represent two standard deviations (systematic errors could constitute an additional ca. 10% uncertainty)]. These results are discussed with respect to the previous literature data and the atmospheric lifetimes of pyrrole and thiophene.     

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     

Rate constants for the gas-phase reactions of the OH radical with a series of monoterpenes at 294 ± 1 K

Using a relative rate technique, rate constants for the gas-phase reactions of the OH radical with a series of monoterpenes have been determined in one atmosphere of air at 294 ± 1 K. Relative to a rate constant for the reaction of OH radicals with 2,3-dimethyl-2-butene of 1.12 × 10^?10 cm³ molecule^?1 sec^?1, the rate constants obtained were (in units of 10^?11 cm³ molecule^?1 sec^?1): α-Pinene, 5.45 ± 0.32; β-pinene, 7.95 ± 0.52; Δ³-carene, 8.70 ± 0.43; d-limonene, 16.9 ± 0.5; α-terpinene, 36.0 ± 4.0; γ-terpinene, 17.6 ± 1.8; α-phellandrene, 31.0 ± 7.1; myrcene, 21.3 ± 1.6; and ocimene (acis-, trans-mixture), 25.0 ± 1.9. These are the first quantitative kinetic data reported for many of these monoterpenes. The rate constants obtained are compared with the available literature data and with a priori estimates based on the number and configuration of substituents around the double bond(s). The tropospheric lifetimes of these monoterpenes with OH radicals, NO₃ radicals and O₃ are estimated and compared. Atmospheric lifetimes with respect to reaction with the OH radical are calculated to range from ～0.75 hr for α-terpinene to ～5 hr for α-pinene.     

Kinetics of the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one under simulated atmospheric conditions

Relative rate coefficients for the reactions of OH with 3‐methyl‐2‐cyclohexen‐1‐one and 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one have been determined at 298 K and atmospheric pressure by the relative rate technique. OH radicals were generated by the photolysis of methyl nitrite in synthetic air mixtures containing ppm levels of nitric oxide together with the test and reference substrates. The concentrations of the test and reference substrates were followed by gas chromatography. Based on the value k(OH + cyclohexene) = (6.77 ± 1.35) × 10^?11 cm³ molecule^?1 s^?1, rate coefficients for k(OH + 3‐methyl‐2‐cyclohexen‐1‐one) = (3.1 ± 1.0) × 10^?11 and k(OH + 3,5,5‐trimethyl‐2‐cyclohexen‐1‐one) = (2.4 ± 0.7) × 10^?11 cm³ molecule^?1 s^?1 were determined. To test the system we also measured k(OH + isoprene) = (1.11 ± 0.23) × 10^?10 cm³ molecule^?1 s^?1, relative to the value k(OH + (E)‐2‐butene) = (6.4 ± 1.28) × 10^?11 cm³ molecule^?1 s^?1. The results are discussed in terms of structure–activity relationships, and the reactivities of cyclic ketones formed in the photo‐oxidation of monoterpene are estimated. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 7–11, 2002     

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     

The temperature dependence of the OH radical reactions with some aromatic compounds under simulated tropospheric conditions

The temperature dependence of the rate coefficients for the OH radical reactions with toluene, benzene, o-cresol, m-cresol, p-cresol, phenol, and benzaldehyde were measured by the competitive technique under simulated atmospheric conditions over the temperature range 258–373 K. The relative rate coefficients obtained were placed on an absolute basis using evaluated rate coefficients for the corresponding reference compounds. Based on the rate coefficient k(OH + 2,3-dimethylbutane) = 6.2 × 10^?12 cm³ molecule^?1s^?1, independent of temperature, the rate coefficient for toluene k_OH = 0.79 × 10^?12 exp[(614 ± 114)/T] cm³ molecule^?1 s^?1 over the temperature range 284–363 K was determined. The following rate coefficients in units of cm³ molecule^?1 s^?1 were determined relative to the rate coefficient k(OH + 1,3-butadiene) = 1.48 × 10^?11 exp(448/T) cm³ molecule^?1 s^?1: o-cresol; k_OH = 9.8 × 10^?13 exp[(1166 ± 248)/T]; 301–373 K; p-cresol; k_OH = 2.21 × 10^?12 exp[(943 ± 449)/T]; 301–373 K; and phenol, k_OH = 3.7 × 10^?13 exp[(1267 ± 233)/T]; 301–373 K. The rate coefficient for benzaldehyde k_OH = 5.32 × 10^?12 exp[(243 ± 85)/T], 294–343 K was determined relative to the rate coefficient k(OH + diethyl ether) = 7.3 × 10^?12 exp(158/T) cm³ molecule^?1 s^?1. The data have been compared to the available literature data and where possible evaluated rate coefficients have been deduced or updated. Using the evaluated rate coefficient k(OH + toluene) = 1.59 × 10^?12 exp[(396 ± 105)/T] cm³ molecule^?1 s^?1, 213–363 K, the following rate coefficient for benzene has been determined k_OH = 2.58 × 10^?12 exp[(?231 ± 84)/T] cm³ molecule^?1 s^?1 over the temperature range 274–363 K and the rate coefficent for m-cresol, k_OH = 5.17 × 10^?12 exp[(686 ± 231)/T] cm³ molecule^?1 s^?1, 299–373 K was determined relative to the evaluated rate coefficient k(OH + o-cresol) = 2.1 × 10^?12 exp[(881 ± 356)/T] cm³ molecule^?1 s^?1. The tropospheric lifetimes of the aromatic compounds studied were calculated relative to that for 1,1,1-triclorethane = 6.3 years at 277 K. The lifetimes range from 6 h for m-cresol to 15.5 days for benzene. © 1995 John Wiley & Sons, Inc.     

Computational study on OH radical reaction with CHF2CHFCHF2(HFC‐245ea) between 200 and 400 K

The rate coefficients of the CHF₂CHFCHF₂ (HFC‐245ea) + OH reaction were computed using G3B3 theory in the temperature range 200 and 400 K. Geometries were optimized for all reactants, transition states, and products at the B3LYP level of theory using 6‐31G* and 6‐311++G** basis sets. Three rotamers (R1, R2, and R3) of CHF₂CHFCHF₂ were identified using a potential energy surface scan. Thirteen independent transition states were identified and confirmed by intrinsic reaction coordinate calculations. The kinetic parameters due to all different transition states are presented in this paper. All the three rotamers were taken into account in computing the rate coefficients. Throughout the temperature range of this study, rotamer R3 contributes significantly (more than 90%), whereas the other two rotamers R1 and R2 contribute less to the total rate coefficient. The rate coefficients for the title reaction were computed to be k = (1.86 ± 0.17) × 10^?13 exp[?(748±26)/T] cm³ molecule^?1s^?1 and (1.25 ± 0.23) × 10^?13 exp[?(587±50)/T] cm³molecule^?1 s^?1 with Wigner's and Eckart's unsymmetrical tunneling methods, respectively, and they are in reasonable agreement with the experimentally measured ones. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 418–430, 2011     

Kinetics of OH reactions with aliphatic thiols

The kinetics of OH reactions with 1–4 carbon aliphatic thiols have been investigated over the temperature range 252–430 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2–4.6 × 10^?11 cm³ molecule^?1 s^?1, -E_act = 0.6–1.0 kcal/mol, A = 0.6–1.2 × 10^?11 cm³ molecule^?1 s^?1. CH₃SH and CH₃SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.     

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.