Gas-phase Reactions Of Cl Atoms Research Articles

Atmospheric chemistry of trifluorodicarbonyls initiated by Cl atoms: Reactivity trends, mechanism, and acid formation yields

Rate coefficients of the gas-phase reactions of Cl atoms with a series of fluorinated diketones (FDKs): CF3C(O)CH2C(O)CH3 (TFP), CF3C(O)CH2C(O)CH2CH3 (TFH) and CF3C(O)CH2C(O)CH(CH3)2 (TFMH), have been measured at (298 ± 2) K and under atmospheric pressure. The experiments were performed using the relative-rate method with a GC-FID detection system. From different determinations and references used, the following rate coefficients were obtained (in cm3/(molecule·sec)): k4(TFP + Cl) = (1.75 ± 0.21) × 10−10, k5(TFH + Cl) = (2.05 ± 0.23) × 10−10, k6(TFMH + Cl) = (2.71 ± 0.34) × 10−10. Reactivity trends of FDKs were discussed and Free Energy Relationships analysis was developed. The expression lgkOH = 1.68 lgkCl + 5.71 was obtained for the reactivity of the studied FDKs together with similar unsaturated VOCs with Cl and OH radicals Additionally, acetic acid (CH3C(O)OH) and trifluoroacetic acid (CF3C(O)OH) were positively identified and quantified as degradation products using in situ FTIR spectroscopy. According to the identified products, atmospheric chemical mechanisms were proposed. The atmospheric implications of the studied reactions were assessed by the estimation of the tropospheric lifetimes of TFP, TFH, and TFMH concerning their reaction with Cl atoms to be 48, 41, and 31 hours, respectively. The relatively short residence in the atmosphere of the fluorocarbons studied will have a local/regional impact with restricted transport. Global warming potential (GWP(20yr)) calculated for the studied fluoro diketones were 0.014, 0.003 and 0.001 for TFP, TFH and TFMH, respectively with a negligible contribution to the greenhouse effect.

Atmospheric sink of β-ocimene and camphene initiated by Cl atoms: kinetics and products at NOxfree-air

Rate coefficients for the gas-phase reactions of Cl atoms with β-ocimene and camphene were determined to be (in units of 10−10 cm3 per molecule per s) 5.5 ± 0.7 and 3.3 ± 0.4, respectively. The experiments were performed by the relative technique in an environmental chamber with FTIR detection of the reactants at 298 K and 760 torr. Product identification experiments were carried out by gas chromatography with mass spectrometry detection (GC-MS) using the solid-phase microextraction (SPME) method employing on-fiber carbonyl compound derivatization with o-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine hydrochloride. An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and cyclic and acyclic terpenes with a conjugated double bond at 298 K is presented. The atmospheric persistence of these compounds was calculated taking into account the measured rate coefficients. In addition, tropospheric chemical mechanisms for the title reactions are postulated.

Atmospheric Chemistry of Tetrahydrofuran, 2-Methyltetrahydrofuran, and 2,5-Dimethyltetrahydrofuran: Kinetics of Reactions with Chlorine Atoms, OD Radicals, and Ozone.

FTIR smog chamber techniques were used to study the kinetics of the gas-phase reactions of Cl atoms, OD radicals, and O3 with the five-membered ring-structured compounds tetrahydrofuran (C4H8O, THF), 2-methyltetrahydrofuran (CH3C4H7O, 2-MTHF), 2,5-dimethyltetrahydrofuran ((CH3)2C4H5O, 2,5-DMTHF), and furan (C4H4O). The rate coefficients determined using relative rate methods were kTHF+Cl = (1.96 ± 0.24) × 10(-10), kTHF+OD = (1.81 ± 0.27) × 10(-11), kTHF+O3 = (6.41 ± 2.90) × 10(-21), k2-MTHF+Cl = (2.65 ± 0.43) × 10(-10), k2-MTHF+OD = (2.41 ± 0.51) × 10(-11), k2-MTHF+O3 = (1.87 ± 0.82) × 10(-20), k2,5-DMTHF+OD = (4.56 ± 0.68) × 10(-11), k2,5-DMTHF+Cl = (2.84 ± 0.34) × 10(-10), k2,5-DMTHF+O3 = (4.58 ± 2.18), kfuran+Cl = (2.39 ± 0.27) × 10(-10), and kfuran+O3 = (2.60 ± 0.31) × 10(-18) molecules cm(-3) s(-1). Rate coefficients of the reactions with ozone were also determined using the absolute rate method under pseudo-first-order conditions. OD radicals, in place of OH radicals, were produced from CD3ONO to avoid spectral overlap of isopropyl and methyl nitrite with the reactants. The kinetics of OD radical reactions are expected to resemble the kinetics of OH radical reactions, and the rate coefficients of the reactions with OD radicals were used to calculate the atmospheric lifetimes with respect to reactions with OH radicals. The lifetimes of THF, 2-MTHF, and 2,5-DMTHF are approximately 15, 12, and 6 h, respectively.

Experimental and computational investigation on the gas phase reaction of p-cymene with Cl atoms.

The rate coefficient for the gas-phase reaction of Cl atoms with p-cymene was determined as a function of temperature (288-350 K) and pressure (700-800 Torr) using the relative rate technique, with 1,3-butadiene and ethylene as reference compounds. Cl atoms were generated by UV photolysis of oxalyl chloride ((COCl)2) at 254 nm, and nitrogen was used as the diluent gas. The rate coefficient for the reaction of Cl atoms with p-cymene at 298 K was measured to be (2.58 ± 1.55) × 10(-10) cm(3) molecule(-1) s(-1). The kinetic data obtained over the temperature range 288-350 K were used to derive an Arrhenius expression: k(T) = (9.36 ± 2.90) × 10(-10) exp[-(488 ± 98)/T] cm(3) molecule(-1) s(-1). Theoretical kinetic calculations were also performed for the title reaction using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) between 250 and 400 K. The calculated rate coefficients obtained over the temperature range 250-400 K were used to derive an Arrhenius expression: k(T) = 5.41 × 10(-13) exp[1837/T] cm(3) molecule(-1) s(-1). Theoretical study indicated that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected. The atmospheric lifetime (τ) of p-cymene due to its reactions with various tropospheric oxidants was estimated, and it was concluded that the reactions of p-cymene with Cl atoms may compete with OH radicals in the marine boundary layer and in coastal urban areas where the concentration of Cl atoms is high.

Temperature dependence of the Cl atom reaction with deuterated methanes.

Kinetic isotope effect (KIE) and reaction rate coefficients, k1-k4, for the gas-phase reaction of Cl atoms with (12)CH3D (k1), (12)CH2D2 (k2), (12)CHD3 (k3), and (12)CD4 (k4) over the temperature range 223-343 K in 630 Torr of synthetic air are reported. Rate coefficients were measured using a relative rate technique with (12)CH4 as the primary reference compound. Fourier transform infrared spectroscopy was used to monitor the methane isotopologue loss. The obtained KIE values were (12)CH3D: KIE1(T) = (1.227 ± 0.004) exp((43 ± 5)/T); (12)CH2D2: KIE2(T) = (1.14 ± 0.20) exp((191 ± 60)/T); (12)CHD3: KIE3(T) = (1.73 ± 0.34) exp((229 ± 60)/T); and (12)CD4: KIE4(T) = (1.01 ± 0.3) exp((724 ± 19)/T), where KIEx(T) = kCl+(12)CH4(T)/kx(T). The quoted uncertainties are at the 2σ (95% confidence) level and represent the precision of our data. The following Arrhenius expressions and 295 K rate coefficient values (in units of cm(3) molecule(-1) s(-1)) were derived from the above KIE using a rate coefficient of 7.3 × 10(-12) exp(-1280/T) cm(3) molecule(-1) s(-1) for the reaction of Cl with (12)CH4: k1(T) = (5.95 ± 0.70) × 10(-12) exp(-(1323 ± 50)/T), k1(295 K) = (6.7 ± 0.8) × 10(-14); k2(T) = (6.4 ± 1.3) × 10(-12) exp(-(1471 ± 60)/T), k2(295 K) = (4.4 ± 0.9) × 10(-14); k3(T) = (4.2 ± 1.0) × 10(-12) exp(-(1509 ± 60)/T), k3(295 K) = (2.53 ± 0.6) × 10(-14); and k4(T) = (7.13 ± 2.3) × 10(-12) exp(-(2000 ± 120)/T), k4(295 K) = (0.81 ± 0.26) × 10(-14). The reported uncertainties in the pre-exponential factors are 2σ and include estimated systematic errors in our measurements and the uncertainty in the reference reaction rate coefficient. The results from this study are compared with previously reported room-temperature rate coefficients for each of the deuterated methanes as well as the available temperature dependent data for the Cl atom reactions with CH3D and CD4. A two-dimensional atmospheric chemistry model was used to examine the implications of the present results to the atmospheric lifetime and vertical variation in the loss of the deuterated methane isotopologues. The relative contributions of the reactions of OH, Cl, and O((1)D) to the loss of the isotopologues in the stratosphere were also examined. The results of the calculations are described and discussed.

Kinetics and mechanism of the tropospheric reaction of 3-hydroxy-3-methyl-2-butanone with Cl atoms.

The relative rate coefficient for the gas-phase reaction of 3-hydroxy-3-methyl-2-butanone (3H3M2B) with Cl atoms was determined under atmospheric conditions (298 ± 2 K, 720 ± 2 Torr). The products of the reaction were identified and quantified. This work provides the first kinetic and mechanistic determinations of the gas-phase reaction of Cl atoms with 3H3M2B. The rate measurements and the products studies were performed in two simulation chambers coupled to the gas chromatography-mass spectrometer (GC-MS) and the Fourier transform infrared (FTIR) techniques, respectively. The obtained average rate coefficient was (1.13 ± 0.17) × 10(-10) cm(3) molecule(-1) s(-1) using propene and 1,3-butadiene as reference compounds. The major primary reaction products observed in this study were (with % molar yields): acetic acid (42.6 ± 4.8) and 2,3-butanedione (17.2 ± 2.3). Results and mechanism are discussed in terms of the structure-reactivity relationship and compared with the reported reactivity with the other atmospheric oxidants. The atmospheric implications derived from this study are discussed as well.

Experimental and computational investigation on the gas phase reaction of ethyl formate with Cl atoms.

The rate coefficient for the gas-phase reaction of Cl atoms with ethyl formate was measured over the temperature range of 268-343 K using relative rate methods, with ethyl chloride as a reference compound. The temperature dependent relative rate coefficients for the ethyl formate + Cl reaction were measured, and the modified Arrhenius expression kethylformate(268-343) = (2.54 ± 0.57) × 10(-23) T(4.1) exp {-(981 ± 102)/T} cm(3) molecule(-1) s(-1) was obtained with 2σ error limits. The room temperature rate coefficient for the title reaction is (9.84 ± 0.79) × 10(-12) cm(3) molecule(-1) s(-1), which is in good agreement with reported values. To complement the experimental measurement, computational methods were used to calculate the rate coefficient for the ethyl formate + Cl reaction atoms using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) and the CCSD (T)/cc-pVDZ//M062X/6-31+g(d,p) level of theory. The temperature dependent Arrhenius expression was obtained to be 2.97 × 10(-18) T(2.4) exp[-(390/T)] cm(3) molecule(-1) s(-1) over the temperature range of 200-400 K. The thermodynamic parameters and branching ratio were calculated. Also, the atmospheric lifetime and global warming potentials (GWPs) were calculated for ethyl formate.

Rate coefficients at 298 K and 1 atm for the tropospheric degradation of a series of C6, C7 and C8 biogenic unsaturated alcohols initiated by Cl atoms

Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated biogenic alcohols at 298 ± 3 K and 1 atm have been measured by the relative technique in an environmental chamber with in situ FTIR detection of reactants. The rate coefficients obtained using 1-butene and isobutene as reference compounds were (in units of 10−10 cm3 molecule−1 s−1): k1((E)-2-hexen-1-ol) = (3.49 ± 0.82), k2((E)-3-hexen-1-ol) = (3.42 ± 0.79), k3 ((Z)-3-hexen-1-ol) = (2.94 ± 0.72), k4((Z)-3-hepten-1-ol) = (3.80 ± 0.86) and k5((Z)-3-octen-1-ol) = (4.13 ± 0.68). This work constitutes the first kinetic study of the reactions cited above. The rate coefficients are compared with those for other unsaturated alcohols and a correlation between the reactivity of unsaturated alcohols toward Cl atoms and the energy of the HOMO of the unsaturated alcohols is presented. Based on the obtained results, the atmospheric lifetimes of the unsaturated alcohols have been estimated and possible atmospheric implications assessed.

Kinetics of the gas-phase reactions of chlorine atoms with naphthalene, acenaphthene, and acenaphthylene.

Reactions of polycyclic aromatic hydrocarbons (PAHs) with chlorine atoms may occur in specific areas such as coastal regions and the marine boundary layer. In this work, rate constants for the gas-phase reactions of naphthalene, acenaphthene, and acenaphthylene with chlorine atoms have been measured using the relative rate technique. Experiments were performed at room temperature (293 ± 2 K) and atmospheric pressure in an atmospheric simulation chamber using a proton-transfer reaction mass spectrometer (PTR-MS) to monitor the concentrations of PAHs and the reference compounds (acetone, methanol, 1,3,5-trimethylbenzene, and isoprene) as a function of time. The rate constants obtained in this work were (in units of cm(3) molecule(-1) s(-1)) (4.22 ± 0.46) × 10(-12), (3.01 ± 0.82) × 10(-10), and (4.69 ± 0.82) × 10(-10) for naphthalene, acenaphthene, and acenaphthylene, respectively. These are the first measurements of the rate constants for gas-phase reactions of Cl atoms with acenaphthene and acenaphthylene. The rate constant determined in this study for the reaction of naphthalene with Cl atoms is not in agreement with the only other previously reported value in the literature. The results are used to assess the potential role of chlorine atom reactions in the atmospheric oxidation of PAHs.

Product distribution study of the Cl-atom initiated oxidation of ethyl methyl sulfide and diethyl sulfide

The products formed in the gas-phase reactions of Cl atoms with (CH3CH2)2S and CH3CH2SCH3 have been investigated in a large volume reactor in NOx-free air at atmospheric pressure and (298 ± 2) K using long path “in situ” FTIR spectroscopy for the analysis. HCl, SO2 and CH3CHO were identified as the major products for both reactions. For the Cl + CH3CH2SCH3 reaction HCHO was also identified as a major product. The yields of the products obtained for the reaction of Cl with (CH3CH2)2S were (59 ± 2) %, (52 ± 5) % and (103 ± 4) % for HCl, SO2 and CH3CHO, respectively. For the reaction of Cl with CH3CH2SCH3 yields of (43 ± 5) %, (55 ± 3) %, (58 ± 3) % and (53 ± 5) % were obtained for HCl, SO2, CH3CHO and HCHO, respectively. This is the first products and mechanistic study for the gas-phase Cl-initiated oxidation of non-CH3SCH3 alkyl sulfides. Comparison with previous results for the reaction of Cl with dimethyl sulfide is made and simple atmospheric degradation mechanisms are postulated to explain the formation of the observed products.

Gas-phase rate coefficients for the reaction of 3-hydroxy-2-butanone and 4-hydroxy-2-butanone with OH and Cl

The reactions of the OH radicals and the Cl atoms with 3-hydroxy 2-butanone (3H2B) and 4-hydroxy 2-butanone (4H2B) were investigated in the gas-phase using relative rate method. The kinetic study on the OH-reactions was carried out using a Pyrex atmospheric chamber at 600–760 Torr of purified air. The temperature ranges were 298–338 K for 3H2B and 278–333 K for 4H2B. A slight negative dependence of the rate coefficients behaviour was observed and the Arrhenius expressions obtained are (in cm3 molecule−1 s−1): k3H2B(OH) = (1.25 ± 0.20) × 10−12exp(612 ± 50/T−1) and k4HB (OH) = (7.50 ± 2.0) × 10−12exp(196 ± 20/T−1). Rate coefficients for the gas-phase reactions of Cl atoms with 3H2B and 4H2B were measured using an atmospheric simulation chamber made of Teflon at 298 ± 3 K and 760 Torr. The obtained rate coefficients (in cm3 molecule−1 s−1) were (4.90 ± 0.45) × 10−11 and (1.45 ± 0.15) × 10−10 for 3H2B and 4H2B, respectively. The obtained data are presented, compared to those reported in the literature and the reactivity trends discussed. The estimated tropospheric lifetimes obtained in this work suggest that once emitted into the atmosphere, 3H2B and 4H2B will be oxidized near the emission sources.

Atmospheric Chemistry of CF3CF═CH2 and (Z)-CF3CF═CHF: Cl and NO3 Rate Coefficients, Cl Reaction Product Yields, and Thermochemical Calculations

Rate coefficients, k, for the gas-phase reactions of Cl atoms and NO(3) radicals with 2,3,3,3-tetrafluoropropene, CF(3)CF═CH(2) (HFO-1234yf), and 1,2,3,3,3-pentafluoropropene, (Z)-CF(3)CF═CHF (HFO-1225ye), are reported. Cl-atom rate coefficients were measured in the fall-off region as a function of temperature (220-380 K) and pressure (50-630 Torr; N(2), O(2), and synthetic air) using a relative rate method. The measured rate coefficients are well represented by the fall-off parameters k(0)(T) = 6.5 × 10(-28) (T/300)(-6.9) cm(6) molecule(-2) s(-1) and k(∞)(T) = 7.7 × 10(-11) (T/300)(-0.65) cm(3) molecule(-1) s(-1) for CF(3)CF═CH(2) and k(0)(T) = 3 × 10(-27) (T/300)(-6.5) cm(6) molecule(-2) s(-1) and k(∞)(T) = 4.15 × 10(-11) (T/300)(-0.5) cm(3) molecule(-1) s(-1) for (Z)-CF(3)C═CHF with F(c) = 0.6. Reaction product yields were measured in the presence of O(2) to be (98 ± 7)% for CF(3)C(O)F and (61 ± 4)% for HC(O)Cl in the CF(3)CF═CH(2) reaction and (108 ± 8)% for CF(3)C(O)F and (112 ± 8)% for HC(O)F in the (Z)-CF(3)CF═CHF reaction, where the quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors. NO(3) reaction rate coefficients were determined using absolute and relative rate methods. Absolute measurements yielded upper limits for both reactions between 233 and 353 K, while the relative rate measurements yielded k(3)(295 K) = (2.6 ± 0.25) × 10(-17) cm(3) molecule(-1) s(-1) and k(4)(295 K) = (4.2 ± 0.5) × 10(-18) cm(3) molecule(-1) s(-1) for CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF, respectively. The Cl-atom reaction with CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF leads to decreases in their atmospheric lifetimes and global warming potentials and formation of a chlorine-containing product, HC(O)Cl, for CF(3)CF═CH(2). The NO(3) reaction has been shown to have a negligible impact on the atmospheric lifetimes of CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF. The energetics for the reaction of Cl, NO(3), and OH with CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF in the presence of O(2) were investigated using density functional theory (DFT).

ChemInform Abstract: Rate Constants for the Gas-Phase Reactions of Cl Atoms with a Series of Hydrofluorocarbons and Hydrochlorofluorocarbons at 298 .+-.2 K.

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Atmospheric Photooxidation of Fluoroacetates as a Source of Fluorocarboxylic Acids

A 1080 L environmental chamber with in situ FTIR spectroscopy detection was used to study the product distribution and the mechanism of the Cl-initiated photooxidation of a series of fluoroacetates. The gas-phase reactions of Cl atoms with ethyl trifluoroacetate (CF(3)C(O)OCH(2)CH(3)), methyl trifluoroacetate (CF(3)C(O)OCH(3)), and methyl difluoroacetate (CF(2)HC(O)OCH(3)) were investigated at 296 +/- 2 K and atmospheric pressure (approximately 760 Torr) of synthetic air. The fate of the fluoroalkoxy radicals formed in the reaction with Cl atoms mainly occurs through (i) an H-atom abstraction by reaction with O(2,) to produce the corresponding fluoroanhydride and (ii) an alpha-ester rearrangement via a five-membered ring intermediate to give the corresponding fluoroacetic acid. The yields of fluoroacids (CF(2)XC(O)OH, with X = H, F) obtained were as follows: 78 +/- 5, 23 +/- 2, and 30 +/- 5% for CF(3)C(O)OCH(2)CH(3), CF(3)C(O)OCH(3), and CF(2)HC(O)OCH(3,), respectively. Yields of <or=20, <or= 80, and <or=55% have been estimated for the anhydride formation from CF(3)C(O)OCH(2)CH(3), CF(3)C(O)OCH(3), and CF(2)HC(O)OCH(3), respectively. Formation of CF(2)O, with yield of 13 +/- 2% has been observed for the reaction of Cl with CF(2)HC(O)OCH(3). The measured yields are rationalized in terms of mechanisms consisting of competitive reaction channels for the radicals formed in the oxidation, that is, reaction with O(2), alpha-ester rearrangement and a decomposition pathway. The stability of the five-membered transition state of the alpha-ester rearrangement is correlated with the acid yields observed for the different fluoroacetates. Atmospheric implications, especially with regard to the fluorocarboxylic acid formation, are discussed.

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.

FTIR gas-phase kinetic study of the reactions of Cl atoms with (CH 3) 2C [dbnd]CHC(O)H and CH 3CH [dbnd]CHC(O)OCH 3

Rate coefficients for the gas-phase reactions of Cl atoms with (CH 3) 2C CHC(O)H and CH 3CH CHC(O)OCH 3 were determined to be (in units of 10 −10 cm 3 molecule −1 s −1): 2.48 ± 0.71 and 2.04 ± 0.56, respectively. The experiments were performed by the relative technique in an environmental chamber with FTIR detection of the reactants at 298 K and 760 Torr. Structure activity relationships were developed for the reactions of Cl with a series of unsaturated esters and aldehydes. In addition, a comparison between the experimentally determined k Cl with k Cl predicted from k vs. HOMO correlations is presented. The atmospheric persistence of these compounds was calculated taking into account the measured rate coefficients.

Temperature dependence of the gas-phase reactions of Cl atoms with propene and 1-butene between 285 < T < 313 K

Relative rate coefficients for the reactions of chlorine atoms with propene and 1-butene have been measured as a function of temperature (285–313 K) at 1 bar total pressure of air using FTIR as detection technique. Such studies are necessary to model the atmospheric chemistry of these alkenes and their impact on the air quality in areas where Cl chemistry is potentially important such as maritime and heavily polluted environments. The temperature dependence can be adequately described by the simple Arrhenius relationship and the following expressions in units of cm 3 molecule −1 s −1 have been obtained: k propene = (1.43 ± 0.35) × 10 −14 exp[(2886 ± 73)/ T] and k 1-butene = (1.60 ± 0.81) × 10 −13 exp[(2235 ± 152)/ T] (errors are 2 σ).

Temperature-dependent rate coefficients for the reactions of Cl atoms with methyl methacrylate, methyl acrylate and butyl methacrylate at atmospheric pressure

Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated esters CH 2 C(CH 3)C(O)OCH 3 (MMA), CH 2 CHC(O)OCH 3 (MAC) and CH 2 C(CH 3)C(O)O(CH 2) 3CH 3 (BMA) have been measured as a function of temperature by the relative technique in an environmental chamber with in situ FTIR detection of reactants. The rate coefficients obtained at 298 K in one atmosphere of nitrogen or synthetic air using propene, isobutene and 1,3-butadiene as reference hydrocarbons were (in units of 10 −10 cm 3 molecule −1 s −1) as follows: k (Cl+MMA) = 2.82 ± 0.93, k (Cl+MAC) = 2.04 ± 0.54 and k (Cl+BMA) = 3.60 ± 0.87. The kinetic data obtained over the temperature range 287–313 K were used to derive the following Arrhenius expressions (in units of cm 3 molecule −1 s −1): k (Cl+MMA) = (13.9 ± 7.8) × 10 −15 exp[(2904 ± 420)/ T], k (Cl+MAC) = (0.4 ± 0.2) × 10 −15 exp[(3884 ± 879)/ T], k (Cl+BMA) = (0.98 ± 0.42) × 10 −15 exp[(3779 ± 850)/ T]. All the rate coefficients display a slight negative temperature dependence which points to the importance of the reversibility of the addition mechanism for these reactions. This work constitutes the first kinetic and temperature dependence study of the reactions cited above. An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and unsaturated and oxygenated volatile organic compounds (VOCs) at 298 K has shown that they can be related by the expression: log k OH = 1.09 log k Cl − 0.10. In addition, a correlation between the reactivity of unsaturated VOCs toward OH radicals and Cl atoms and the HOMO of the unsaturated VOC is presented. Tropospheric implications of the results are also discussed.

Relative kinetic measurements of rate coefficients for the gas-phase reactions of Cl atoms and OH radicals with a series of methyl alkyl esters

Abstract Relative kinetic studies have been performed on the reactions of Cl atoms with a series of methyl alkyl esters in a 405-liter borosilicate glass chamber at (298 ± 3) K and one atmosphere of synthetic air using in situ FTIR spectroscopy to monitor the reactants. Rate coefficients (in units of cm3 molecule−1 s−1) were determined for the following compounds: methyl acetate (2.48 ± 0.58) × 10−12; methyl propanoate (1.68 ± 0.36) × 10−11; methyl butanoate (4.77 ± 0.87) × 10−11; methyl pentanoate (7.84 ± 1.15) × 10−11; methyl hexanoate (1.09 ± 0.31) × 10−10; methyl heptanoate (1.56 ± 0.37) × 10−10; methyl cyclohexane carboxylate (3.32 ± 0.76) × 10−10; methyl-2-methyl butanoate (9.41 ± 1.39) × 10−11. In addition rate coefficients (in units of 10−11 cm3 molecule−1 s−1) have been obtained for the reactions of OH radicals with the following compounds: methyl butanoate (3.55 ± 0.71), methyl pentanoate (5.41 ± 1.08), and methyl-2-methyl butanoate (4.08 ± 0.82). Using the kinetic rate data tropospheric lifetimes for the methyl alkyl esters with respect to their reactions with OH, and Cl have been estimated for typical ambient air concentrations of these oxidants.

Atmospheric Chemistry of Sulfuryl Fluoride: Reaction with OH Radicals, Cl Atoms and O3, Atmospheric Lifetime, IR Spectrum, and Global Warming Potential

Sulfuryl fluoride (SO2F2) is a radiatively active industrial chemical released into the atmosphere in significant (ktonne/ year) quantities. The potential for SO2F2 to contribute to radiative forcing of climate change needs to be assessed. Long path length FTIR/smog chamber techniques were used to investigate the kinetics of the gas-phase reactions of Cl atoms, OH radicals, and O3 with SO2F2, in 700 Torr total pressure of air or N2 at 296 +/- 1 K. Upper limits of k(Cl + SO2F2) < 9 x 10(-19), k(OH + SO2F2) < 1.7 x 10(-14) and k(O3 + SO2F2) < 5.5 x 10(-24) cm3 molecule(-1) s(-1) were determined. Reaction with Cl atoms, OH radicals, or O3 does not provide an efficient removal mechanism for SO2F2. The infrared spectrum of SO2F2 is reported and a radiative efficiency of 0.196 W m(-2) ppbv(-1) was calculated. Historic production data estimates are presented which provide an upper limit for expected atmospheric concentrations. The radiative forcing of climate change associated with emissions of SO2F2 depends critically on the atmospheric lifetime of SO2F2. Further research is urgently needed to define the magnitude of potential nonatmospheric sinks.