Relative Rate Method Research Articles

Kinetics and Products of the Reactions of OH Radicals with 4,4-Dimethyl-1-pentene and 3,3-Dimethylbutanal at 296 ± 2 K

Using a relative rate method, rate constants have been measured for the reactions of OH radicals with 4,4-dimethyl-1-pentene [(CH(3))(3)CCH(2)CH=CH(2)] and its major reaction product, 3,3-dimethylbutanal [(CH(3))(3)CCH(2)CHO], at 296 +/- 2 K and atmospheric pressure of air. The rate constants obtained were 2.41 x 10(-11) and 2.73 x 10(-11) cm(3) molecule(-1) s(-1), respectively, with estimated uncertainties of +/-10%. The products identified and quantified by gas chromatography with mass spectrometry and/or flame ionization detection from the 4,4-dimethyl-1-pentene reaction were acrolein [CH(2)=CHCHO], 3,3-dimethylbutanal, and a molecular weight 112 carbonyl attributed to 4,4-dimethyl-2-pentenal [(CH(3))(3)CCH=CHCHO], with formation yields of 2.7 +/- 0.5%, 59 +/- 6%, and 3.4 +/- 0.6%, respectively. Using direct air sampling atmospheric pressure ionization mass spectrometry, additional products of molecular weight 146, 177, and 193 were observed, and on the basis of expected reaction schemes these are attributed to the dihydroxycarbonyl HOCH(2)C(CH(3))(2)CH(2)C(O)CH(2)OH, the hydroxynitrates (CH(3))(3)CCH(2)CH(OH)CH(2)ONO(2) and/or (CH(3))(3)CCH(2)CH(ONO(2))CH(2)OH, and the dihydroxynitrate O(2)NOCH(2)C(CH(3))(2)CH(2)CH(OH)CH(2)OH, respectively. The hydroxynitrates were also tentatively identified by gas chromatography, with a summed yield of approximately 15%. Acrolein and 4,4-dimethyl-2-pentenal arise from H-atom abstraction from the three equivalent CH(3) groups and the 3-position CH(2) group, and the sum of their formation yields (6.1 +/- 0.8%) is expected to be very close to the fraction of the overall reaction proceeding by H-atom abstraction.

Reactions of chloroethenes with atomic chlorine in air at atmospheric pressure

Relative rate method at the temperature of 298 K and pressure of 1013 hPa and GC-MS detection were used for the study of kinetics of the reactions of Cl atoms with H2C=CCl2, cis-ClHC=CHCl, trans-ClHC=CHCl, ClHC=CCl2, and Cl2C=CCl2. The reaction products were identified by FTIR spectroscopy. A mechanism for the atmospheric degradation of chloro-ethenes has been suggested.

Uptake of NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> to Saharan dust, ambient urban aerosol and soot: a relative rate study

Abstract. The uptake of NO3 and N2O5 to Saharan dust, ambient aerosols and soot was investigated using a novel and simple relative rate method with simultaneous detection of both NO3 and N2O5. The use of cavity ring down spectroscopy to detect both trace gases enabled the measurements to be carried out at low mixing ratios (<500 pptv or 1×1010 molecule cm−3). The uptake coefficient ratio, γ(NO3)/γ(N2O5), was determined to be 0.9±0.4 for Saharan dust, independent of relative humidity, NO3 or N2O5 mixing ratio and exposure time. Ambient (urban) aerosols showed a very limited capacity to take up N2O5 but were reactive towards NO3 with γ(NO3)/γ(N2O5)>15. A value of γ(NO3)/γ(N2O5)~1.5–3 was obtained when using candle generated soot. The relative rate obtained for Saharan dust can be placed on an absolute basis using our recently determined value of γ(N2O5)=1×10−2 to give γ(NO3)=9×10−3, which is significantly smaller than the single previous value. With the present uptake coefficient, reaction of NO3 with mineral dust will generally not contribute significantly to its NO3 loss in the boundary atmosphere or to the nitration of mineral dust.

Kinetics and Mechanism of Chlorine-Atom-Initiated Oxidation of Allyl Alcohol, 3-Buten-2-ol, and 2-Methyl-3-buten-2-ol

The gas-phase reactions of Cl atoms with allyl alcohol (k(1)), 3-buten-2-ol (k(2)), and 2-methyl-3-buten-2-ol (k(3)) at 296 +/- 2 K have been investigated using absolute and relative rate methods in 1-700 Torr of N(2) diluent. Absolute rate studies were performed using pulsed laser photolysis/vacuum ultraviolet laser-induced fluorescence spectroscopy techniques. Relative rate studies were performed using smog chamber/Fourier transform infrared spectroscopy techniques. The absolute and relative rate studies gave consistent results. The kinetics of the reactions are dependent on pressure over the range studied. Molar yields for HCl production in 700 Torr of N(2) for reactions of chlorine atoms with allyl alcohol, 3-buten-2-ol, and 2-methyl-3-buten-2-ol were measured to be 0.26 +/- 0.03, 0.23 +/- 0.03, and 0.12 +/- 0.02, respectively. The chlorine-atom-initiated oxidation of 2-methyl-3-buten-2-ol in 700 Torr of air gave the following products (molar yields): acetone (47 +/- 4%), chloroacetaldehyde (47 +/- 5%), and HCHO (7.2 +/- 0.6%). The observation of substantial and indistinguishable yields of acetone and chloroacetaldehyde products indicates that a major fraction of the reaction proceeds via addition of chlorine atoms to the terminal carbon atom. The results are discussed with respect to the literature data.

Kinetics of the gas-phase reactions of NO3 radicals with ethyl acrylate, n-butyl acrylate, methyl methacrylate and ethyl methacrylate

Abstract The relative rate method has been used to determine the rate constants for the gas-phase reactions of NO3 radicals with a series of acrylate esters: ethyl acrylate (k1), n-butyl acrylate (k2), methyl methacrylate (k3) and ethyl methacrylate (k4) at 298 ± 1 K and 760 Torr. The obtained rate constants are k1 = (1.8 ± 0.25) × 10−16 cm3 molecule−1 s−1, k2 = (2.1 ± 0.33) × 10−16 cm3 molecule−1 s−1, k3 = (3.6 ± 1.2) × 10−15 cm3 molecule−1 s−1, k4 = (4.9 ± 1.7) × 10−15 cm3 molecule−1 s−1. The experimental rate constants are in good agreement with theoretical rate constants calculated by an algorithm of the correlation between the rate constants and the orbital energies for the reactions of unsaturated VOCs with NO3 radicals. In addition, the atmospheric lifetimes of the compound against NO3 attack are estimated and the results show that NO3 reactions contribute little to the atmospheric losses of acrylate esters except in polluted regions.

Atmospheric Chemistry of Isopropyl Methyl Methylphosphonate and Dimethyl N,N-Dimethylphosphoroamidate

Rate constants for the reactions of OH radicals with isopropyl methyl methylphosphonate [(CH(3))(2)CHOP(O)(CH(3))OCH(3); IMMP] and dimethyl N,N-dimethylphosphoroamidate [(CH(3)O)(2)P(O)N(CH(3))(2); DMDMPA] have been measured over the temperature range 283-350 K and atmospheric pressure of air using a relative rate method. The rate expressions obtained were 2.72 x 10(-13) e((1642+/-144)/T) cm(3) molecule(-1) s(-1) (6.72 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + IMMP and 6.05 x 10(-13) e((1185+/-144)/T) cm(3) molecule(-1) s(-1) (3.23 x 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + DMDMPA. In addition, rate constants for the reactions of NO(3) radicals and O(3) with IMMP were measured at 296 +/- 2 K, of (4.8 +/- 2.1) x 10(-16) and <7 x 10(-20) cm(3) molecule(-1) s(-1), respectively. Products of the OH radical-initiated reactions were investigated using gas chromatography, in situ atmospheric pressure ionization mass spectrometry (API-MS), and in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH + IMMP reaction, the major initial products appear to be CH(3)OP(O)(CH(3))OC(O)CH(3) + (*)CH(3), with subsequent reactions of the methyl radical in the presence of NO(x) leading to HCHO, CH(3)ONO, and CH(3)ONO(2). For the OH + DMDMPA reaction, (CH(3)O)(2)P(O)N(CH(3))CHO was observed as a significant product. Possible reaction mechanisms are discussed.

Kinetics study of gas-phase reactions of erythro/ threo-CF 3CHFCHFC 2F 5 with OH radicals at 253–328 K

Rate constants for reactions of erythro-CF 3CHFCHFC 2F 5 and threo-CF 3CHFCHFC 2F 5 with OH radicals were determined by means of a relative rate method in an 11.5-dm 3 reaction chamber at 253 –328 K: k 1 ( erythro-CF 3CHFCHFC 2F 5 + OH) = (9.60 ± 3.39) × 10 –13 exp[–(1680 ± 100)/ T] and k 2 ( threo-CF 3CHFCHFC 2F 5 + OH) = (6.60 ± 2.06) × 10 –13 exp[–(1580 ± 90)/ T] cm 3 molecule –1 s –1.

Kinetic study of the reaction of chlorine atoms with bromomethane and D-bromomethane in the gas phase

Abstract The kinetics of the gas-phase reactions of chlorine atoms with bromomethane CH 3 Br and D-bromomethane CD 3 Br was studied experimentally. The relative rate method was applied using Cl + CH 4 as the reference reaction. The rate constants for H-abstraction from CH 3 Br ( k H ) and D-abstraction from CD 3 Br ( k D ) were measured in the temperature range of 298–527 K and at a total pressure of 100 Torr. The temperature dependencies of the rate constants are described by the expressions: k H = (1.43 ± 0.22) × 10 −11 × exp(−1040 ± 30/ T ) and k D = (1.36 ± 0.31)×10 −11 × exp(−1595 ± 30/ T ) cm 3 molecule −1 s −1 . The kinetic isotope effect, described by the ratio k H / k D , was found to be (1.07 ± 0.14) × exp(555 ± 20/ T ).

Rate coefficients and products for gas‐phase reactions of chlorine atoms with cyclic unsaturated hydrocarbons at 298 K

AbstractRate coefficients for the reaction of Cl atoms with cycloalkenes have been determined using the relative rate method, at 298 K and atmospheric pressure of N2. Reference molecule wasn‐hexane, and the concentrations of the organics were followed by gas chromatographic analysis. Cl atoms were prepared by photolysis of trichloroacetyl chloride at 254 nm. The relative rates of reactions of Cl atoms with cycloalkenes, with respect ton‐hexane, are measured as 1.12 ± 0.38, 1.31 ± 0.14, and 1.69 ± 0.18 for cyclopentene, cyclohexene, and cycloheptene, respectively. Considering the absolute value of the rate coefficient of the reaction of Cl atom withn‐hexane as 3.03 ± 0.06 × 10−10cm3molecule−1s−1, the rate coefficient values for cyclopentene, cyclohexene, and cycloheptene are calculated to be (3.39 ± 1.08) × 10−10, (3.97 ± 0.43) × 10−10, and (5.12 ± 0.55) × 10−10cm3molecule−1s−1, respectively. The experiments for each molecule were repeated six to eight times, and the slopes and the rate coefficients given above are the average values of these measurements, and the quoted error includes 2σ as well as all other uncertainties in the measurement and calculations. The rate coefficient increases linearly with the number of carbon atoms, with an increment per additional CH2group being (8.7 ± 1.6) × 10−12cm3molecule−1s−1. Chloroketones and chloroalcohols, along with unsaturated ketones and alcohols, were found to be the major products of Cl‐atom‐initiated oxidation of cycloalkenes in the presence of air. The atmospheric implications of these results are discussed, along with a comparison with the reported structure activity relationships. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 42: 98–105, 2010

Experimental and Theoretical Analysis of the Kinetics of the Reaction of Atomic Bromine with 1,4-Dioxane

The rate coefficient for the reaction of atomic bromine with 1,4-dioxane was measured from approximately 300 to 340 K using the relative rate method. Iso-octane and iso-butane were used as reference compounds, and the experiments were made in a bath of argon containing up to 210 Torr of O(2) at total pressures between 200 and 820 Torr. The rate coefficients were not affected by changes in pressure or O(2) concentration over our range of experimental conditions. The ratios of rate coefficients for the reaction of dioxane relative to the reference compound were put on an absolute basis by using the published absolute rate coefficients for the reference reactions. The variation of the experimentally determined rate coefficients with temperature for the reaction of Br with 1,4-dioxane can be given by k(1)(exp)(T) = (1.4 +/- 1.0) x 10(-11)exp[-23.0 +/- 1.8) kJ mol(-1)/(RT)] cm(3) molecule(-1) s(-1). We rationalized our experimental results in terms of transition state theory with molecular data from quantum chemical calculations. Molecular geometries and frequencies were obtained from MP2/aug-cc-pVDZ calculations, and single-point energies of the stationary points were obtained at CCSD(T)/CBS level of theory. The calculations indicate that the 1,4-dioxane + Br reaction proceeds in an overall endothermic addition-elimination mechanism via a number of intermediates. The rate-determining step is a chair-to-boat conformational change of the Br-dioxane adduct. The calculated rate coefficients, given by k(1)(calc)(T) = 5.6 x 10(-11)exp[-26.6 kJ mol(-1)/(RT)] cm(3) molecule(-1) s(-1), are in very good agreement with the experimental values. Comparison with results reported for the reactions of Br with other ethers suggests that this multistep mechanism differs significantly from that for abstraction of hydrogen from other ethers by atomic bromine.

Reaction Rate Coefficients of OH Radicals and Cl Atoms with Ethyl Propanoate,n-Propyl Propanoate, Methyl 2-Methylpropanoate, and Ethyln-Butanoate

Kinetics of the reactions of OH radicals and Cl atoms with four saturated esters have been investigated. Rate coefficients for the gas-phase reactions of OH radicals with ethyl propanoate (k(1)), n-propyl propanoate (k(2)), methyl 2-methylpropanoate (k(3)), and ethyl n-butanoate (k(4)) were measured using a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. At (296 +/- 2) K, the rate coefficients obtained by the two methods were in good agreement. Significant curvatures in the Arrhenius plots have been observed in the temperature range 243-372 K for k(1), k(3), and k(4). The rate coefficients for the reactions of the four esters with Cl atoms were determined using the relative rate method at (296 +/- 2) K and atmospheric pressure. The values obtained are presented, compared with the literature values when they exist, and discussed. Reactivity trends and atmospheric implications for these esters are also presented.

Kinetics of the Gas-Phase Reactions of OH and NO3 Radicals and O3 with Allyl Alcohol and Allyl Isocyanate

Rate constants for the gas-phase reactions of OH radical, NO(3) radical, and ozone with allyl alcohol (AAL) and allyl isocyanate (AIC) have been measured using relative rate methods at atmospheric pressure in purified air. The experimental Arrhenius expression obtained for the reaction of the OH radical with AAL is (1.68 +/- 0.89) x 10(-12) x exp(1100/T) cm(3) molecule(-1) s(-1), for T = 282-315 K; the Arrhenius expression for the reaction of OH radical with AIC is (1.94 +/- 1.04) x 10(-14) x exp(2207/T) cm(3) molecule(-1) s(-1), for T = 282-317 K, where the indicated errors are one least-squares standard deviation. All OH radical reaction rate constants have been measured relative to k(OH + alpha-pinene) and k(OH + 1,3,5-trimethylbenzene). The rate constant for the gas-phase reaction of OH radical with allyl alcohol-d(6) isotopomer (AAL-d(6)) has been measured at T = 298 K, and the value is 5.10 x 10(-11) cm(3) molecule(-1) s(-1). The kinetic isotope effect is small, with k(AAL)/k(AAL-d(6)) = 1.32. Rate constants for the gas-phase reactions of NO(3) radical with AAL [relative to k(NO(3) +methacrolein)] and O(3) [relative to k(O(3) + beta-pinene)] have been measured, and the values are 7.7 x 10(-15) cm(3) molecule(-1) s(-1) at T = 298 K and 1.6 x 10(-17) cm(3) molecule(-1) s(-1) at T = 296 K, respectively. Rate constants for the gas-phase reactions of NO(3) radical and O(3) with AIC have been measured, and the values are 9.4 x 10(-16) cm(3) molecule(-1) s(-1) at T = 299 K and 5.54 x 10(-18) cm(3) molecule(-1) s(-1) at T = 299 K, respectively. Multireference ab initio calculations at the MRMP2/6-311G(d,p) level have been carried out for reactions of OH radical with AAL and AIC. Results indicate that prereactive hydrogen bonded complexes form in the entrance channels for these reactions.

Kinetic study of the reactions of Cl atoms with α,β-unsaturated carbonyl compounds at atmospheric pressure and structure activity relations (SARs)

Abstract The kinetics of the reactions of Cl atoms with three unsaturated carbonyl compounds at 298 K and atmospheric pressure were investigated for the first time using the GC–FID technique. Rate coefficients (in cm 3 molecule −1 s −1 ) of k 1 (Cl + CH 2 CHC(O)CH 2 CH 3 ) = (2.91 ± 1.10) × 10 −10 , k 2 (Cl + CH 2 CHOC(O)CH 2 CH 3 ) = (2.06 ± 0.36) × 10 −10 and k 3 (Cl + CH 2 CHC(O)OCH 2 CH 3 ) = (2.53 ± 0.46) × 10 −10 were obtained using the relative rate method with different references. Structure activity relationships (SARs) were developed for the reactions of Cl with a wide range of unsaturated compounds. On the basis of our kinetic measurements, tropospheric lifetimes of the studied unsaturated compounds are estimated.

Temperature Dependence of the Rate Coefficients for the Reactions of Atomic Bromine with Toluene, Tetrahydrofuran, and Tetrahydropyran

The rate coefficients for the reactions of atomic bromine with toluene, tetrahydrofuran, and tetrahydropyran were measured from approximately 295 to 362 K using the relative rate method. Iso-octane was used as the reference compound for the reaction with toluene, and iso-octane and toluene were used as the reference compounds for the reaction with tetrahydrofuran; tetrahydrofuran was used as the reference compound for the reaction with tetrahydropyran. The rate coefficients were found to be unaffected by changes in pressure and oxygen concentration. The rate coefficient ratios were converted to absolute values using the absolute rate coefficient for the reaction of Br with the reference compound. The absolute rate coefficients, in the units cm(3) molecule(-1) s(-1), for the reaction of Br with toluene are given by k(T) = (3.7 +/- 1.7) x 10(-12) exp(-(1.63 +/- 0.15) x 10(3)/T), for the reaction of Br with tetrahydrofuran by k(T) = (3.7 +/- 2.7) x 10(-10) exp(-(2.20 +/- 0.22) x 10(3)/T), and for the reaction of Br with tetrahydropyran by k(T) = (3.6 +/- 1.8) x 10(-10) exp(-(2.35 +/- 0.16) x 10(3)/T). The uncertainties represent one standard deviation. The Arrhenius parameters for these reactions are compared with results in the literature for dimethyl ether, diethyl ether, and a series of saturated hydrocarbons, and the effects of structural variation on these parameters are identified.

Kinetic study of the reaction of chlorine atoms with chloromethane in the gas phase

The kinetics of the gas phase reactions of chlorine atoms with chloromethane and D-chloromethane CD 3Cl was studied experimentally. The relative rate method was applied using Cl + CH 3Br as the reference reaction. The rate constants for H-abstraction from CH 3Cl ( k H) and D-abstraction from CD 3Cl ( k D) were measured in the temperature range of 298–527 K and at a total pressure of 100 Torr. The derived temperature dependencies of the rate constants are given by k H = (1.7 ± 0.1) × 10 −11 × exp(−1040 ± 10/ T) and k D = (1.3 ± 0.2) × 10 −11 × exp(−1470 ± 10/ T) cm 3 molecule −1 s −1. The kinetic isotope effect, described by the ratio k H/ k D, was (1.35 ± 0.05) × exp(420 ± 10/ T).

Kinetics of the gas‐phase reactions of cyclo‐CF2CFXCHXCHX – (X = H, F, Cl) with OH radicals at 253–328 K

AbstractRate constants were determined for the reactions of OH radicals with halogenated cyclobutanes cyclo‐CF2CF2CHFCH2(k1), trans‐cyclo‐CF2CF2CHClCHF(k2), cyclo‐CF2CFClCH2CH2(k3), trans‐cyclo‐CF2CFClCHClCH2(k4), and cis‐cyclo‐CF2CFClCHClCH2(k5) by using a relative rate method. OH radicals were prepared by photolysis of ozone at a UV wavelength (254 nm) in 200 Torr of a sample reference H2OO3O2He gas mixture in an 11.5‐dm3 temperature‐controlled reaction chamber. Rate constants of k1 = (5.52 ± 1.32) × 10−13 exp[–(1050 ± 70)/T], k2 = (3.37 ± 0.88) × 10−13 exp[–(850 ± 80)/T], k3 = (9.54 ± 4.34) × 10−13 exp[–(1000 ± 140)/T], k4 = (5.47 ± 0.90) × 10−13 exp[–(720 ± 50)/T], and k5 = (5.21 ± 0.88) × 10−13 exp[–(630 ± 50)/T] cm3 molecule−1 s−1 were obtained at 253–328 K. The errors reported are ± 2 standard deviations, and represent precision only. Potential systematic errors associated with uncertainties in the reference rate constants could add an additional 10%–15% uncertainty to the uncertainty of k1–k5. The reactivity trends of these OH radical reactions were analyzed by using a collision theory–based kinetic equation. The rate constants k1–k5 as well as those of related halogenated cyclobutane analogues were found to be strongly correlated with their CH bond dissociation enthalpies. We consider the dominant tropospheric loss process for the halogenated cyclobutanes studied here to be by reaction with the OH radicals, and atmospheric lifetimes of 3.2, 2.5, 1.5, 0.9, and 0.7 years are calculated for cyclo‐CF2CF2CHFCH2, trans‐cyclo‐CF2CF2CHClCHF, cyclo‐CF2CFClCH2CH2, trans‐cyclo‐CF2CFClCHClCH2, and cis‐cyclo‐CF2CFClCHClCH2, respectively, by scaling from the lifetime of CH3CCl3. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 532–542, 2009

Kinetics of the reactions of chlorine atoms with a series of acetates

The kinetics of the reactions of Cl atoms with a series of alkyl acetates were investigated using relative and absolute rate methods in 2–700 Torr of N 2 at room temperature. Consistent results were obtained using the two methods. The data from the absolute rate measurements were more precise and were (in units of 10 −11 cm 3 molecule −1 s −1): ethyl acetate, 1.76 ± 0.11; n-propyl acetate, 7.19 ± 0.11; i-propyl acetate, 1.97 ± 0.24; n-butyl acetate, 15.8 ± 0.94; i-butyl acetate, 9.97 ± 0.60; s-butyl acetate, 8.01 ± 0.48; and t-butyl acetate, 1.64 ± 0.10. The reactivity of alkyl acetates is discussed in terms of structure–activity relationship.

Kinetics of gas‐phase reactions of CH3OCH2CF3, CH3OCH3, CH3OCH2CH3, CH3CH2OCH2CH3, and CHF2CF2OCH2CF3 with NO3 radicals at 298 K

AbstractRate 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 &lt; 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 &gt;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

Rate Constants for the Gas-Phase Reactions of NO3Radicals and O3with C6−C141-Alkenes and 2-Methyl-1-alkenes at 296 ± 2 K

Rate constants for the gas-phase reactions of NO(3) radicals and O(3) with a series of C(6)-C(14) 1-alkenes and 2-methyl-1-alkenes have been measured at 296 +/- 2 K and atmospheric pressure of air using relative rate methods. For the NO(3) radical reactions, the rate constants obtained (in units of 10(-14) cm(3) molecule(-1) s(-1)) were: 1-hexene, 2.00 +/- 0.16; 1-octene, 2.35 +/- 0.15; 1-decene, 2.55 +/- 0.16; 1-dodecene, 2.79 +/- 0.36; 1-tetradecene, 2.87 +/- 0.21; 2-methyl-1-pentene, 43.8 +/- 2.3; 2-methyl-1-hexene, 52.4 +/- 2.5; 2-methyl-1-octene, 57.8 +/- 2.6; 2-methyl-1-nonene, 60.8 +/- 2.9; 2-methyl-1-undecene, 60.8 +/- 3.3; 2-methyl-1-tridecene, 60.3 +/- 3.4; and cycloheptene, 49.4 +/- 2.0. For the O(3) reactions, the rate constants obtained (in units of 10(-17) cm(3) molecule(-1) s(-1)) were: 1-hexene, 0.898 +/- 0.054; 1-heptene, 1.05 +/- 0.07; 1-octene, 1.01 +/- 0.04; 1-decene, 1.11 +/- 0.05; 1-dodecene, 1.38 +/- 0.14; 1-tridecene, 1.92 +/- 0.12; 1-tetradecene, 2.44 +/- 0.24; 2-methyl-1-pentene, 1.26 +/- 0.13; 2-methyl-1-heptene, 1.35 +/- 0.05; 2-methyl-1-octene, 1.38 +/- 0.06; 2-methyl-1-decene, 1.48 +/- 0.07; 2-methyl-1-undecene, 1.46 +/- 0.11; and 2-methyl-1-tridecene, 2.85 +/- 0.42. The rate constants for the NO(3) radical reactions significantly increase with increasing carbon number, attaining a plateau at > or = C(14) for the 1-alkenes and at C(10)-C(14) for the 2-methyl-1-alkenes. In contrast, the rate constants for O(3) reactions increase only slightly with increasing carbon number up to approximately C(10) for the 1-alkenes and approximately C(12) for the 2-methyl-1-alkenes, with the significant increase in the measured rate constants for the > C(10) 1-alkenes and > C(12) 2-methyl-1-alkenes possibly being due to heterogeneous reactions. Reasons for the observed trends in NO(3) radical and O(3) reaction rate constants with alkene carbon number are discussed.

Gas-phase reaction of ( E)-β-farnesene with ozone: Rate coefficient and carbonyl products

The gas-phase ozonolysis of ( E)-β-farnesene was investigated in a 3.91 m 3 atmospheric simulation chamber at 296 ± 2 K and relative humidity of around 0.1%. The relative rate method was used to determine the reaction rate coefficient of (4.01 ± 0.17) × 10 −16 cm 3 molecule −1 s −1, where the indicated errors are two least-squares standard deviations and do not include uncertainties in the rate coefficients for the reference compounds (γ-terpinene, cis-cyclooctene and 1,5-cyclooctadiene). Gas phase carbonyl products were collected using a denuder sampling technique and analyzed with GC/MS following derivatization with O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine (PFBHA). The reaction products detected were acetone, 4-oxopentanal, methylglyoxal, 4-methylenehex-5-enal, 6-methylhept-5-en-2-one, and ( E)-4-methyl-8-methylenedeca-4,9-dienal. A detailed mechanism for the gas-phase ozonolysis of ( E)-β-farnesene is proposed, which accounts for all of the products observed in this study. The results of this work indicate that the atmospheric reaction of ( E)-β-farnesene with ozone has a lifetime of around 1 h and is another possible source of the ubiquitous carbonyls, acetone, 4-oxopentanal and 6-methylhept-5-en-2-one in the atmosphere.