Reaction Of Cl Atoms Research Articles

Kinetics, products and mechanisms of the OH radicals and Cl atoms reactions with trans-2-octene and cycloheptene

Relative rate coefficients for the gas-phase reactions of OH radicals and Cl atoms with trans-2-octene (k1-OH and k2-Cl) and cycloheptene (k3-OH and k4-Cl) have been determined by in situ Fourier Transform Infrared Spectroscopy (FTIR). The experiments were carried out at 298 ± 2 K and atmospheric pressure (760 ± 10) Torr using synthetic air as bath gas. The following rate coefficients (in units of cm3 molecule−1 s−1) were obtained for the reactions of trans-2-octene and cycloheptene with OH radicals and Cl atoms: k1-OH = (8.51 ± 1.86) × 10−11, k2-Cl = (4.47 ± 1.09) × 10−10, k3-OH = (7.84 ± 1.78) × 10−11, k4-Cl = (5.46 ± 1.01) × 10−10, respectively. This is the first kinetic study for the reactions of trans-2-octene with Cl atoms and the first rate coefficient determination for the title reactions by in situ FTIR spectroscopy. The kinetic data were compared with previously reported values for similar compounds and reactivity trends were developed. Complementary, products identification studies were performed in similar conditions to the kinetic experiments by the in situ FTIR and Gas Chromatography coupled to mass spectrometry (GC-MS). The atmospheric chemical mechanisms were postulated for the first time for both unsaturated compounds. In addition, the atmospheric implications of these reactions were assessed through the estimation of the tropospheric lifetimes, Photochemical Ozone Creation Potential (POCP) and fates of these compounds in the troposphere.

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.

Temperature‐dependent kinetics of the gas‐phase reactions of Cl atoms with nopinone, ketolimonene, and myrtenal

AbstractIn this study, the gas phase reaction of chlorine atoms with three first‐generation oxidation products of monoterpene: (myrtenal C10H14O, nopinone C9H14O, and ketolimonene C9H14O) were investigated using a relative technique method. These compounds result from the atmospheric oxidation of monoterpene compounds such as α/β – pinene and limonene. Experiments were performed at temperature range 298–353 K and atmospheric pressure in synthetic air bath gas. Cl atoms were generated by UV photolysis of dichloride (Cl2). The reaction was followed using a proton‐transfer reaction mass spectrometer (PTR‐MS) and/or Fourier‐transform infrared spectroscopy (FTIR) to monitor the concentrations of the investigated species simultaneous with several reference compounds as a function of time. The rate constants were obtained and the Arrhenius expressions (cm3 molecule−1 s−1) obtained were established over the temperature range of 298–353 K:knopinone + Cl = (5.0 ± 1.2) × 10−10 exp ( − (406 ± 78) /T)kketolimonene + Cl = (8.88 ± 1.3) × 10−10 exp( − (246 ± 46)/T)kmyrtenal + Cl = (13.5 ± 6.4) × 10−10 exp( − (535 ± 153)/T)Based on rate constants, the atmospheric lifetimes (τ) of targeted compounds with respect to reaction with chlorine atoms were estimated and expected to be less than 1 day. There results led to conclude that the reaction with chlorine atoms can be an effective tropospheric loss pathway mainly in regions presenting relatively high chlorine concentrations.

Hydroxy esters atmospheric degradation: OH and Cl reactivity, products distribution and fate of the alkoxy radicals formed

Kinetic studies of the reaction of ethyl glycolate HOCH2C(O)OCH2CH3 with OH radicals (kOH) and Cl atoms (kCl) have been conducted by the relative method using a glass atmospheric reactor by “in situ” Fourier Transform Infrared (FTIR) and Gas Chromatography equipped with flame ionization detection by Solid Phase Micro Extraction (GC-FID/SPME) at room temperature and atmospheric pressure. The following relative rate coefficients were determined using several reference compounds and two different techniques: kEG + OH-FTIR = (4.36 ± 1.21) × 10−12; kEG + OH-GC-FID= (3.90 ± 0.74) × 10−12; and kEG + Cl-GC-FID= (6.40 ± 0.72) × 10−11 all values in units of cm3.molecule−1.s−1. Complementary product studies were performed under comparable conditions to the kinetic tests, in order to identify the reaction products and to postulate their tropospheric oxidation mechanisms. The reaction of OH radicals and Cl atoms with ethyl glycolate initiates via H-atom abstraction from alkyl groups of the molecule. Formic acid was positively identified as a reaction product by FTIR. On the other hand, formaldehyde, acetaldehyde, glycolic acid; and formic acid were identified by the GC-MS technique. The Structure–Activity Relationship, (SAR) calculations were also implemented to estimate the more favorable reaction pathways and compare them with the products identified. Tropospheric lifetimes of τOH = 34 h and τCl = 5.5 days were estimated to determine how these investigated reactions might affect the air quality. In this sense, average ozone production of [O3] = 0.75 and a Photochemical Ozone Creation Potential, POCP, of 38 were calculated for the hydroxyl ester studied.

Atmospheric degradation of chloroacetoacetates by Cl atoms: Reactivity, products and mechanism in coastal and industrialized areas

Kinetic studies of the reaction of Cl atoms with ethyl 2-chloroacetoacetate, CH3C(O)CHClC(O)OCH2CH3, (k1) and methyl 2-chloroacetoacetate, CH3C(O)CHClC(O)OCH3, (k2) have been developed for the first time using SPME/GC-FID and in situ FTIR spectroscopy at (298 ± 2) K and 1000 mbar in glass atmospheric chambers. Relative rate coefficients obtained by Fourier Transform Infrared Spectroscopy (FTIR) using different reference compounds, were the following (in cm3.molecule−1.s−1): kE2CAA-FTIR= (2.41 ± 0.57) × 10−10 and kM2CAA-FTIR= (2.16 ± 0.85) × 10−10. Similar and reproducible values were obtained using Gas Chromatography equipped with Flame Ionization Detection coupled with Solid Phase Micro Extraction (SPME), kE2CAA-GC-FID = (2.54 ± 0.81) × 10−10 and kM2CAA-GC-FID = (2.34 ± 0.87) × 10−10 all values in units of cm3.molecule−1.s−1. In addition, product studies were performed in similar conditions to the kinetic experiments to identify the reaction products and postulate their tropospheric degradation mechanisms. The reaction of Cl atoms with saturated esters initiates via H-atom abstraction from the alkyl groups of the molecule. Formyl chloride, chloroacetone, and acetyl chloride were positively identified as reaction products by FTIR. On the other hand, acetyl chloride, 1,1,1-trichloropropan-2-one, 1,1-dichloropropan-2-one, 1-chloropropan-2-one, ethyl chloroformate, and methyl chloroformate were identified by the GC-MS technique. Structure–Activity Relationship (SAR), calculations were also performed to estimate the more favorable reactions pathways in agreement with the products observed. The atmospheric implications of these reactions were assessed by the estimation of the residence times of the chloroesters studied as following: τCl-E2CAA = 1.47 days, and τCl-M2CAA = 1.57 days. Additionally, the possible impact of the emission of chloro acetoacetates in rain acidification was evaluated from the moderate Acidification Potentials (AP), 0.19, and 0.21 obtained for E2CAA and M2CAA, respectively.

Room temperature rate coefficients for the reaction of chlorine atoms with a series of volatile methylsiloxanes (L2‐L5, D3‐D6)

AbstractThe kinetics of chlorine (Cl) atom reactions with a series of volatile methylsiloxanes (VMS) including hexamethyldisiloxane (L2), octamethyltrisiloxane (L3), decamethyltetrasiloxane (L4), dodecamethylpentasiloxane (L5), hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6) were investigated in relative rate experiments at room temperature and atmospheric pressure. The experiments were carried out in a 0.2 m3 PFA Teflon chamber, employing proton‐transfer‐reaction time‐of‐flight mass spectrometry (PTR‐ToF‐MS) as the chemical‐analytical tool. The following relative and absolute reaction rate coefficients were obtained using isoprene as reference compound (kVMS/kisoprene; kVMS × 1010 cm3 molec−1 s −1): L2 (0.32 ± 0.02; 1.31 ± 0.21), L3 (0.38 ± 0.00; 1.56 ± 0.23), L4 (0.48 ± 0.01; 1.98 ± 0.29), L5 (0.54 ± 0.03; 2.22 ± 0.34), D3 (0.14 ± 0.02; 0.56 ± 0.13), D4 (0.26 ± 0.01; 1.05 ± 0.16), D5 (0.36 ± 0.02; 1.46 ± 0.22), D6 (0.39 ± 0.02; 1.61 ± 0.25). The following relative and absolute reaction rate coefficients were obtained using toluene as reference compound (kVMS/ktoluene; kVMS × 1010 cm3 molec−1 s −1): L2 (1.59 ± 0.18; 0.95 ± 0.14), L3 (2.25 ± 0.14; 1.35 ± 0.16), L4 (2.38 ± 0.01; 1.43 ± 0.14), L5 (3.57 ± 0.11; 2.14 ± 0.22), D3 (0.87 ± 0.01; 0.52 ± 0.05), D4 (1.48 ± 0.12; 0.89 ± 0.11), D5 (2.02 ± 0.15; 1.21 ± 0.15), D6 (2.54 ± 0.11; 1.52 ± 0.17). Our data confirm that reactions with Cl atoms need to be taken into account when assessing the decomposition of VMS in Cl‐rich tropospheric environments.

Rate constant and branching ratio of the reaction of ethyl peroxy radicals with methyl peroxy radicals.

The cross-reaction of ethyl peroxy radicals (C2H5O2) with methyl peroxy radicals (CH3O2) (R1) has been studied using laser photolysis coupled to time resolved detection of the two different peroxy radicals by continuous wave cavity ring down spectroscopy (cw-CRDS) in their AÃ-X̃ electronic transition in the near-infrared region, C2H5O2 at 7602.25 cm-1, and CH3O2 at 7488.13 cm-1. This detection scheme is not completely selective for both radicals, but it is demonstrated that it has great advantages compared to the widely used, but unselective UV absorption spectroscopy. Peroxy radicals were generated from the reaction of Cl-atoms with the appropriate hydrocarbon (CH4 and C2H6) in the presence of O2, whereby Cl-atoms were generated by 351 nm photolysis of Cl2. For different reasons detailed in the manuscript, all experiments were carried out under excess of C2H5O2 over CH3O2. The experimental results were best reproduced by an appropriate chemical model with a rate constant for the cross-reaction of k = (3.8 ± 1.0) × 10-13 cm3 s-1 and a yield for the radical channel, leading to CH3O and C2H5O, of (ϕ1a = 0.40 ± 0.20).

Kinetics and products study of the reaction of Cl atoms with methyl dichloroacetate: reactivity, mechanism, and environmental implications

Polychlorinated esters released to the atmosphere can suffer photooxidation, that lead persistent Cl-containing compounds, with harmful effects to the environment at local, regional and global scale.

Atmospheric chemistry of methoxyflurane: Reaction with Cl atoms and further degradation

AbstractA dual‐level direct dynamics technique is used to explore the kinetic properties of the reaction of Cl atoms with methoxyflurane (CH3OCF2CHCl2). The energy profiles of two reaction channels of the two conformers are refined with the interpolated single‐point energies (ISPE) method at the CCSD(T)/M06‐2X level. The canonical variational transition state theory (CVT) with a small‐curvature tunneling (SCT) correction is used to assess the rate coefficients over a wide temperature range (250–500 K) in order to get accurate results. At a temperature of 296 K, the calculated CVT/SCT rate coefficient kCl = 2.71 × 10−13 cm3 molecule−1 s−1 is found to be in reasonably good agreement with the experimental result. Our calculations demonstrate that CH3OCF2CHCl2 + Cl → CH2OCF2CHCl2 + HCl (R1) reaction is the key pathway and a prominent conduit for CH3OCF2CHCl2 degradation in the troposphere. The atmospheric loss of C•H2OCF2CHCl2 and CH3OCF2C•Cl2 radicals are discussed. The rate coefficient value of the oxidation of the primary product HC(O)OCF2CHCl2 with the Cl atoms is 1.8 × 10−14 cm3 molecule−1 s−1, and for the first time, the rate coefficient of HC(O)OCF2CHCl2 + OH reaction has also been reported here.

Reaction of Cl Atom with c-C5F8 and c-C5HF7: Relative and Absolute Measurements of Rate Coefficients and Identification of Degradation Products.

Partially and fully fluorinated olefins are a class of compounds with relatively short atmospheric lifetimes and low 100-year global warming potentials, compared to their saturated predecessors, which are used or considered as refrigerants, propellants, solvents, and other end-uses. The cyclic unsaturated compounds c-C5F8 and c-C5HF7 are currently under consideration as etching agents for the semiconductor industry. In this study, we expand on our previous work on the reaction of the OH radical with c-C5F8 and c-C5HF7 and report the rate coefficients, k, for the gas-phase reaction of the Cl atom with c-C5F8 and c-C5HF7 over a range of temperature (245-367 K) and pressure (100-200 Torr of He or N2 and 0 to 4.8 Torr O2) using a pulsed laser photolysis-resonance fluorescence (PLP-RF) technique. In addition, a relative rate (RR) technique, employing multiple reference compounds, was used to study the Cl atom reactions at 296 K, 100 and 630 Torr (N2 or air) total pressure. Reaction rate coefficients, k1, of the Cl atom reaction with c-C5F8 were found to be independent of pressure, over the pressure range used in this work, with k1(296 K), derived as an average of results from the PLP-RF and RR techniques being (1.07 ± 0.02) × 10-12 cm3 molecule-1 s-1 and k1(T) = (7.76 ± 0.73) × 10-13 × (exp[(98 ± 26)/T]) cm3 molecule-1 s-1, where the quoted error limits represent the 2σ data precision. Rate coefficients, k2, for the Cl atom + c-C5HF7 reaction were measured to be k2(296 K) = (4.61 ± 0.10) × 10-12 cm3 molecule-1 s-1 and k2(T) = (7.42 ± 0.89) × 10-13 × (exp[(540 ± 32)/T]) cm3 molecule-1 s-1. The Cl atom temporal profiles, observed with the PLP-RF technique, indicate that the Cl atom with c-C5F8 and c-C5HF7 reactions lead to adduct formation. The equilibrium constants for adduct formation were derived in this work, and a second-law analysis was used to obtain ΔH and ΔS values of -18.5 ± 0.4 kcal mol-1, -30.9 ± 1.2 cal K-1 mol-1, and -13.9 ± 0.5 kcal mol-1, -27.6 ± 1.1 cal K-1 mol-1 for the c-C5F8 and c-C5HF7 reactions, respectively. The Cl-initiated degradation of c-C5F8 and c-C5HF7 in the presence of O2 was studied and stable products were identified via infrared spectroscopy using experimental or theoretically derived spectra from our previous OH reaction work. For c-C5F8, FC(O)CF2CF2CF2C(O)F and FC(O)C(O)F were observed with molar yields of 0.80 and 0.10, respectively. For c-C5HF7, we observed the formation of HC(O)CF2CF2CF2C(O)F and HC(O)C(O)F with a combined molar yield of 0.72. Carbonyl difluoride, F2CO, was also a major product in the decomposition of c-C5F8 and c-C5HF7. The oxidation mechanism of the Cl-initiated degradation of c-C5F8 and c-C5HF7 is discussed. Based on the combined findings from this and our previous work, the atmospheric implications from the use of c-C5F8 and c-C5HF7 are presented.

Kinetic and mechanism of the reaction between Cl and several mono-methyl branched alkanes

Branched alkanes are ubiquitous in the troposphere and play an important role in the chemical processes. In this work, the rate constants and products for the reaction of Cl atoms with 3-methylhexane and 2-methylheptane were measured at room temperature (298 ± 0.2 K) and atmospheric pressure using a conventional relative rate method. The rate constants of 3-methylhexane and 2-methylheptane in units of cm3/(mol·sec) are (3.09 ± 0.31) × 10−10 and (3.67 ± 0.40) × 10−10, respectively. Furthermore, the corresponding atmospheric lifetime of the studied branched alkanes with Cl was 6.92-89.90 hours and 5.82-75.69 hours, respectively. The estimated atmospheric lifetimes indicated that the reaction with Cl atoms could be the most important atmospheric degradation pathway for 3-methylhexane and 2-methylheptane. Primary gas-phase products of the reactions were identified and quantified, and particle-phase products were also obtained. The atmosphere oxidation mechanism of Cl atoms with 3-methylhexane and 2-methylheptane is proposed. The SOA yields of 3-methylhexane and 2-methylheptane from the reaction of Cl atoms were determined to be 7.96% ± 0.89% and 13.35% ± 1.50% respectively. Overall, the results reveal that the primary loss process of branched alkanes is the reaction with Cl atoms, which impacts its degradation on a regional scale.

Self-Reaction of Acetonyl Peroxy Radicals and Their Reaction with Cl Atoms.

The rate constant for the self-reaction of the acetonyl peroxy radicals, CH3C(O)CH2O2, has been determined using laser photolysis/continuous wave cavity ring down spectroscopy (cw-CRDS). CH3C(O)CH2O2 radicals have been generated from the reaction of Cl atoms with CH3C(O)CH3, and the concentration time profiles of four radicals (HO2, CH3O2, CH3C(O)O2, and CH3C(O)CH2O2) have been determined by cw-CRDS in the near-infrared. The rate constant for the self-reaction was found to be k = (5.4 ± 1.4) × 10-12 cm3 s-1, in good agreement with a recently published value (Zuraski, K., et al. J. Phys. Chem. A 2020, 124, 8128); however, the branching ratio for the radical path was found to be ϕ1b = (0.6 ± 0.1), which is well above the recently published value (0.33 ± 0.13). The influence of a fast reaction of Cl atoms with the CH3C(O)CH2O2 radical became evident under some conditions; therefore, this reaction has been investigated in separate experiments. Through the simultaneous fitting of all four radical profiles to a complex mechanism, a very fast rate constant of k = (1.35 ± 0.8) × 10-10 cm3 s-1 was found, and experimental results could be reproduced only if Cl atoms would partially react through H-atom abstraction to form the Criegee intermediate with a branching fraction of ϕCriegee = (0.55 ± 0.1). Modeling the HO2 concentration-time profiles was possible only if a subsequent reaction of the Criegee intermediate with CH3C(O)CH3 was included in the mechanism leading to HO2 formation with a rate constant of k = (4.5 ± 2.0) × 10-14 cm3 s-1.

Study on the reaction of 3-methyl-2-butenal and 3-methylbutanal with Cl atoms: kinetics and reaction mechanism

The reaction of Cl atoms with two C5 aldehydes (3-methyl-2-butenal and 3-methylbutanal) were investigated by proton-transfer-reaction mass spectrum (PTR-MS) using smog chamber at 298 ± 1 K and 760 Torr. A relative rate method was used to determine the rate constants of the title reactions with m-xylene and trans-2-butene as reference compounds: (3.04 ± 0.18) × 10−10 and (2.07 ± 0.14) × 10−10 cm3/(molecule⋅sec) for 3-methyl-2-butenal and 3-methylbutanal, respectively. Additionally, the gas-phase products were also identified by PTR-MS, and the possible reaction mechanisms were proposed basing on the identified products. The detected gas-phase products are similar for two C5 aldehydes reactions, mainly including small molecules of aldehydes, ketones and chlorinated aldehyde compounds. The atmospheric lifetimes (τ) calculated for 3-methyl-2-butenal (τ = 7.0 hr, marine boundary layer (MBL)) and 3-methylbutanal (τ = 10.3 hr, MBL) according to the obtained rate constants. The results indicate that Cl atoms at MBL are competitive with OH radicals for the degradation contribution of C5 aldehyde compounds.

Barrierless HNO3 formation from the hydrolysis reaction of NO2 with Cl atom in the atmosphere

Nitric acid (HNO3) is one of the main pollutants in the atmosphere and has an important effect on the air pollution. However, the formation pathways of HNO3 are still poorly understood in the marine boundary layer (MBL). Here, we show evidence of the formation of HNO3 from chlorine (Cl) radical and nitrogen dioxide (NO2), with 1–3 water molecules, as well as on the air-water interface, based on the direct Born-Oppenheimer molecular dynamics (BOMD) simulation. The relative free energy change along the reaction coordinates for the (Cl)(NO2)(H2O)1 (monohydrate) system was calculated using thermodynamic integration, revealing that the monohydrate system exhibited no free energy barrier and was 26.5 kcal mol−1 exergonic. This suggests that the formation of HNO3 from the monohydrate system is thermodynamically favorable. For all the systems studied, the formation of HNO3 was directly observed using BOMD simulations, and only one water molecule participates in the reaction. However, loop structures, which were expected to be ubiquitous on the air-water interface, were not observed. This study identifies the importance of the reactions of Cl atom, NO2, and water molecules in the formation of HNO3 in the MBL region.

Experimental and Computational Investigations of the Tropospheric Photooxidation Reactions of 1,1,1,3,3,3-Hexafluoro-2-Methyl-2-Propanol Initiated by OH Radicals and Cl Atoms.

The gas-phase kinetics for the reactions of OH radicals and Cl atoms with 1,1,1,3,3,3-hexafluoro-2-methyl-2-propanol (HF2M2P) were measured at temperatures between 268 and 363 K using the relative rate experimental technique. Methane and acetonitrile were used as reference compounds to measure the rate coefficients of the title reactions. For the reactions of HF2M2P with OH radicals and Cl atoms, the rate coefficients were measured to be (7.07 ± 1.21) × 10-15 and (2.85 ± 0.54) × 10-14 cm3 molecule-1 s-1, respectively, at 298 K. The obtained Arrhenius expressions for the reactions of HF2M2P with OH radicals and Cl atoms are kHF2M2P+OHExp-(268-363K) = (7.84 ± 0.75) × 10-14 exp [-(717 ± 59)/T] and kHF2M2P+ClExp-(268-363K) = (3.21 ± 0.45) × 10-12 exp [-(1395 ± 83)/T] cm3 molecule-1 s-1. In addition to the experimental measurements, computational kinetic calculations were also performed for the title reactions at the M06-2X/MG3S//M06-2X/6-31 + G(d,p) level of theory using advanced methods such as the canonical variational transition-state theory coupled with small curvature tunneling corrections at temperatures between 200 and 400 K. Theoretical calculations reveal that the H-abstraction from the CH3 group is a more favorable reaction channel than that from the OH group. Thermochemistry, branching ratios, cumulative atmospheric lifetime, global warming potential, acidification potential, and photochemical ozone creation potential of HF2M2P were calculated in the present investigation.

Kinetic and Mechanistic Investigation for the Gas-Phase Tropospheric Photo-oxidation Reactions of 2,2,2-Trifluoroethyl Acrylate with OH Radicals and Cl Atoms.

The photo-oxidation of 2,2,2-trifluoroethyl acrylate (TFEA) (CH2CHC(O)OCH2CF3) initiated by OH radicals and Cl atoms was investigated in tropospheric conditions using both experimental and computational methods. The kinetic measurements were carried out in the temperature range of 268-363 K using the relative rate method. The rate coefficients for the reaction of OH radicals with TFEA were measured relative to diethyl ether, ethylene, and acetaldehyde. The rate coefficients for the reaction of Cl atoms with TFEA were measured relative to propylene and ethylene. The rate coefficients for the reaction of TFEA with OH radicals and Cl atoms at 298 K were experimentally measured to be kR1exp-298K = (1.41 ± 0.31) × 10-11 cm3 molecule-1 s-1 and kR2exp-298K = (2.37 ± 0.50) × 10-10 cm3 molecule-1 s-1, respectively. The deduced temperature-dependent Arrhenius expressions for the reactions of OH radicals and Cl atoms with TFEA are kR1exp-(268-363K) = (9.82 ± 1.37) × 10-12 exp. [(812 ± 152)/T] cm3 molecule-1 s-1 and kR2exp-(268-363K) = (1.25 ± 0.17) × 10-11 exp. [(862 ± 85)/T] cm3 molecule-1 s-1, respectively. To complement our experimental results, computational calculations were performed at CCSD(T)/cc-pVDZ//M062X/6-31+G(d,p) and CCSD(T)/cc-pVDZ//MP2/6-311+G(d,p) levels of theory, respectively, in combination with canonical variational transition-state theory (CVT) with small curvature tunneling (SCT) over the temperature range of 200-400 K. Furthermore, the degradation mechanisms initiated by OH radicals and Cl atoms were proposed for the titled reactions based on the qualitative analysis of the products in gas chromatography-mass spectrometry (GC-MS) and gas chromatography-infrared spectroscopy (GC-IR). Atmospheric implications, thermochemistry, and branching ratios for the titled reactions are discussed in detail in the paper.

Kinetic Measurements of Cl Atom Reactions with C5–C8 Unsaturated Alcohols

The reactions of five structurally similar unsaturated alcohols, i.e., (Z)-2-penten-1-ol, (E)-2-hexen-1-ol, (E)-3-hexen-1-ol, (Z)-3-hexen-1-ol, and 1-octen-3-ol, with Cl atoms in the gas phase, were investigated at 296 ± 2 K and 1 atm by the relative-rate kinetic technique using a 600-L Teflon reaction chamber. Selected ion flow tube mass spectrometry (SIFT-MS) was used simultaneously to monitor the decay of the alcohols of interest and selected reference compounds. Tetrahydrofuran (THF), propan-1-ol, and octane were used as reference compounds. Chlorine atoms were produced by the photolysis of molecular chlorine (Cl2) using broadband actinic lamps near 365 nm. The estimated rate constant values (in 10−10 cm3∙molecule−1∙s−1) followed the order 2.99 ± 0.53 ((Z)-2-penten-1-ol) < 3.05 ± 0.59 ((E)-3-hexen-1-ol) < 3.15 ± 0.58 ((Z)-3-hexen-1-ol) < 3.41 ± 0.65 ((E)-2-hexen-1-ol) < 4.03 ± 0.77 (1-octen-3-ol). The present work provides the first value of the rate constant for the reaction of 1-octen-3-ol with Cl atoms. The results are discussed and interpreted in relation to other studies where literature data are available. The structure–activity relationship and the atmospheric implications are discussed as well.

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

AbstractKinetics 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.

Atmospheric fate of a series of saturated alcohols: kinetic and mechanistic study

Abstract. The atmospheric fate of a series of saturated alcohols (SAs) was evaluated through kinetic and reaction product studies with the main atmospheric oxidants. These SAs are alcohols that could be used as fuel additives. Rate coefficients (in cm3 molecule−1 s−1) measured at ∼298 K and atmospheric pressure (720±20 Torr) were as follows: k1 ((E)-4-methylcyclohexanol + Cl) = (3.70±0.16) ×10-10, k2 ((E)-4-methylcyclohexanol + OH) = (1.87±0.14) ×10-11, k3 ((E)-4-methylcyclohexanol + NO3) = (2.69±0.37) ×10-15, k4 (3,3-dimethyl-1-butanol + Cl) = (2.69±0.16) ×10-10, k5 (3,3-dimethyl-1-butanol + OH) = (5.33±0.16) ×10-12, k6 (3,3-dimethyl-2-butanol + Cl) = (1.21±0.07) ×10-10, and k7 (3,3-dimethyl-2-butanol + OH) = (10.50±0.25) ×10-12. The main products detected in the reaction of SAs with Cl atoms (in the absence/presence of NOx), OH radicals, and NO3 radicals were (E)-4-methylcyclohexanone for the reactions of (E)-4-methylcyclohexanol, 3,3-dimethylbutanal for the reactions of 3,3-dimethyl-1-butanol, and 3,3-dimethyl-2-butanone for the reactions of 3,3-dimethyl-2-butanol. Other products such as formaldehyde, 2,2-dimethylpropanal, and acetone have also been identified in the reactions of Cl atoms and OH radicals with 3,3-dimethyl-1-butanol and 3,3-dimethyl-2-butanol. In addition, the molar yields of the reaction products were estimated. The products detected indicate a hydrogen atom abstraction mechanism at different sites on the carbon chain of alcohol in the case of Cl reactions and a predominant site in the case of OH and NO3 reactions, confirming the predictions of structure–activity relationship (SAR) methods. Tropospheric lifetimes (τ) of these SAs have been calculated using the experimental rate coefficients. Lifetimes are in the range of 0.6–2 d for OH reactions, 7–13 d for NO3 radical reactions, and 1–3 months for Cl atoms. In coastal areas, the lifetime due to the reaction with Cl decreases to hours. The calculated global tropospheric lifetimes, and the polyfunctional compounds detected as reaction products in this work, imply that SAs could contribute to the formation of ozone and nitrated compounds at local, regional, and even global scales. Therefore, the use of saturated alcohols as additives in diesel blends should be considered with caution.

Kinetics and Mechanistic Study for Gas Phase Tropospheric Photo-oxidation Reactions of 2,2,2-Trifluoroethyl Methacrylate with OH Radicals and Cl Atoms: An Experimental and Computational Approach.

The photo-oxidation reactions of 2,2,2-trifluoroethyl methacrylate (TFEMA) initiated by OH radicals and Cl atoms were investigated via experimental as well as computational methodologies. The rate coefficients for these reactions were investigated using the relative rate technique (RR) at temperatures between 268 and 363 K. The rate coefficients for the reaction of OH radicals with TFEMA were measured with reference to diethyl ether and propylene. Propane and propylene were used in the kinetic measurements as reference compounds. At 298 K, experimentally obtained rate coefficients for the reaction of TFEMA with OH radicals and Cl atoms are kTFEMA+OHexp-298K = (2.81 ± 0.54) × 10-11 and kTFEMA+Clexp-298K = (1.91 ± 0.44) × 10-10 cm3 molecule-1 s-1, respectively. The Arrhenius expression obtained for the respective reactions are kTFEMA+OHexp-(268-363K) = (7.32 ± 0.62) × 10-12 exp[(400 ± 53) and kTFEMA+Clexp-(268-363K) = (4.10 ± 0.78) × 10-12 exp[(1228 ± 115)/T]. To further complement our experimental findings, rate coefficients were also calculated computationally for the reactions of OH radicals and Cl atoms with TFEMA at CCSD(T)/cc-pVDZ//M062X/6-31+G(d,p) and CCSD(T)/cc-pVDZ//MP2/6-31+G(d,p) levels of theory using canonical variational transition state theory (CVT) with small curvature tunneling (SCT) over the temperature range 200-400 K. Moreover, to analyze the end products formed during the title reactions, qualitative analyses were performed using gas chromatography-mass spectrometry (GC-MS) and gas chromatography-infrared spectroscopy (GC-IR) as analytical tools and degradation mechanisms were proposed for the title reactions. Branching ratios, thermochemical parameters of these reactions, and their impact on the troposphere were discussed.