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 radical reactions in pulse radiolyzed RHF — CO2(SF6)-O2-NO gaseous mixtures; RHF = CH3CH2F, CH3CHF2, CH3CF3, CH2FCF3

The kinetics of the peroxy radicals RHFO₂ reactions with NO has been studied by using pulse radiolysis and UV absorption spectroscopy. The rate constants of interaction of oxygen atoms with NO − k ₂ = 2.2±0.2·10⁻¹² cm³·s⁻¹ and NO₂ − k ₃ = 2.1±0.2·10⁻¹¹ cm³·s⁻¹ were found in agreement with the literature values. The bath gases (SF₆ or CO₂) have got minor effect on the rate constants of RHFO₂+NO→NO₂+prod. reactions; RHFO₂ = CH₃CH₂O₂, CH₃CHFO₂, CH₃CF₂O₂, CF₃CH₂O₂, CF₃CHFO₂. The obtained rate coefficients are in the scope of the literature values, although they are lower than those recommended in NIST database. The reasons are discussed.     

Kinetics for the gas‐phase reactions of OH radicals with the hydrofluoroethers CH2FCF2OCHF2, CHF2CF2OCH2CF3, CF3CHFCF2OCH2CF3, and CF3CHFCF2OCH2CF2CHF2 at 268–308 K

Rate constants were determined for the reactions of OH radicals with the hydrofluoroethers (HFEs) CH₂FCF₂OCHF₂(k₁), CHF₂CF₂OCH₂CF₃ (k₂), CF₃CHFCF₂OCH₂CF₃(k₃), and CF₃CHFCF₂OCH₂CF₂CHF₂(k₄) by using a relative rate method. OH radicals were prepared by photolysis of ozone at UV wavelengths (>260 nm) in 100 Torr of a HFE–reference–H₂O–O₃–O₂–He gas mixture in a 1‐m³ temperature‐controlled chamber. By using CH₄, CH₃CCl₃, CHF₂Cl, and CF₃CF₂CF₂OCH₃ as the reference compounds, reaction rate constants of OH radicals of k₁ = (1.68) × 10^?12 exp[(?1710 ± 140)/T], k₂ = (1.36) × 10^?12 exp[(?1470 ± 90)/T], k₃ = (1.67) × 10^?12 exp[(?1560 ± 140)/T], and k₄ = (2.39) × 10^?12 exp[(?1560 ± 110)/T] cm³ molecule^?1 s^?1 were obtained at 268–308 K. The errors reported are ± 2 SD, and represent precision only. We estimate that the potential systematic errors associated with uncertainties in the reference rate constants add a further 10% uncertainty to the values of k₁–k₄. The results are discussed in relation to the predictions of Atkinson's structure–activity relationship model. The dominant tropospheric loss process for the HFEs studied here is considered to be by the reaction with the OH radicals, with atmospheric lifetimes of 11.5, 5.9, 6.7, and 4.7 years calculated for CH₂FCF₂OCHF₂, CHF₂CF₂OCH₂CF₃, CF₃CHFCF₂OCH₂CF₃, and CF₃CHFCF₂OCH₂CF₂CHF₂, respectively, by scaling from the lifetime of CH₃CCl₃. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 239–245, 2003     

Rate constants for the gas-phase reactions of Cl atoms with a series of hydrofluorocarbons and hydrochlorofluorocarbons at 298 ± 2 K

A relative rate method has been used to determine rate constants for the gas-phase reactions of a series of hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) at 298 ± 2 K and atmospheric pressure of air. Based on a rate constant for the reaction of the Cl atom with CH₄ of (1.0 ± 0.2) ? 10^?13 cm³ molecule^?1 s^?1 at 298 K, the following Cl atom reaction rate constants (in units of 10^?15 cm³ molecule^?1 s^?1) were obtained: CH₃F, 340 ± 70; CH₃CHF₂, 240 ± 50; CH₂FCl, 110 ± 25; CHFCl₂, 21 ± 4; CHCl₂CF₃, 14 ± 3; CHFClCF₃, 2.7 ± 0.6; CH₃CFCl₂, 2.4 ± 0.5; CHF₂Cl, 2.0 ± 0.4; CH₂FCF₃, 1.6 ± 0.3; CH₃CF₂Cl, 0.37 ± 0.08; and CHF₂CF₃, 0.24 ± 0.05. These Cl atom reaction rate constants are compared with literature data and with the corresponding OH radical reaction rate constants. © John Wiley & Sons, Inc.     

Absolute rate constants for the reactions ofOHradicals withCH3CH2OH, CF2HCH2OHandCF3CH2OH

Summary Pulsed laser photolysis with resonance fluorescence monitoring of OH radicals was applied at T = 300±2 K to obtain the rate constants of k₁= (3.38±0.60)x10^-12, k₂= (2.52±0.44)x10^-13and k₃ = (1.06±0.30)x10^-13cm³molecule^-1s^-1with 2σprecision given for the overall reactions OH + CH₃CH₂OH (1), OH + CF₂HCH₂OH (2) and OH + CF₃CH₂OH (3), respectively. k₂is the first direct kinetic data for the reaction of OH radicals with CF₂HCH₂OH reported in the literature.</o:p>     

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 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.     

Measurement of the rate constants of the reactions of the chlorine atom with C<Subscript>3</Subscript>F<Subscript>7</Subscript>I and CF<Subscript>3</Subscript>I using the resonance fluorescence of chlorine atoms

The rate constants of the reactions of the chlorine atom with C₃F₇I (k ₁) and CF₃I (k ₂) have been measured using the resonance fluorescence of chlorine atoms in a flow reactor at 295 K: k ₁ = (5.2 ± 0.3) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k ₂ = (7.4 ± 0.6) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. No iodine atoms have been detected in the reaction products.     

Photochromic transformations in solutions of 8,8′-diquinolyl disulfide and di(mercaptoquinolinato)nickel(<Emphasis Type="SmallCaps">II</Emphasis>)

The nature of intermediate species and their reactions were studied by laser pulse photolysis for a photochromic system consisting of 8,8′-diquinolyl disulfide (RSSR) and a planar Ni^II complex di(mercaptoquinolinato)nickel(II) (Ni(SR)₂) in toluene and benzene solutions. Under exposure to laser radiation, disulfide RSSR dissociates to two RS^· radicals, whose spectrum has an intense absorption band with a maximum at λ = 400 nm (ε = 8400 L mol⁻¹ cm⁻¹). The radicals disappear by recombination (2k _rec = 4.6 · 10⁹ L mol⁻¹ s⁻¹). In the presence of the Ni(SR)₂ complex, coordination of the radical (k _coord = 4.4 · 10⁹ L mol⁻¹ s⁻¹) competes with recombination to form a radical complex RS^· Ni(SR)₂ having an intense absorption band with a maximum at 460 nm (ε = 16 600 L mol⁻¹ cm⁻¹). This species decays in the second-order reaction (2k = 4.6 · 10⁴ L mol⁻¹ s⁻¹). Since the photochromic system returns to the initial state, the reaction of two radical complexes is assumed to produce radical recombination and reduction of the disulfide and Ni(SR)₂ complex. Analysis of the kinetic data showed that some RS^· radicals decay in the microsecond time interval due to the reaction with the RS^· Ni(SR)₂ radical complex (k = 3.1 · 10⁹ L mol⁻¹ s⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2291–2300, October, 2005.     

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     

Mechanism and kinetics of the production of hydroxymethyl hydroperoxide in ethene/ozone/water gas-phase system

The mechanism and kinetics of the production of hydroxymethyl hydroperoxide (HMHP) in ethene/ ozone/water gas-phase system were investigated at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The reactants were monitored in situ by long path FTIR spectroscopy. Peroxides were measured by an HPLC post-column fluorescence technique after sampling with a cold trap. The rate constants (k3) of reaction CH2O2 H2O→HMHP (R3) determined by fitting model calculations to ex-perimental data range from (1.6―6.0)×10?17 cm3·molecule?1·s?1. Moreover, a theoretical study of reac-tion (R3) was performed using density functional theory at QCISD(T)/6-311 (2d,2p)//B3LYP/6-311 G(2d, 2p) level of theory. Based on the calculation of the reaction potential energy surface and intrinsic reac-tion coordinates, the classic transitional state theory (TST) derived k3 (kTST), canonical variational tran-sition state theory (CVT) derived k3 (kCVT), and the corrected kCVT with small-curvature tunneling (kCVT/SCT) were calculated using Polyrate Version 8.02 program to be 2.47×10-17, 2.47×10-17 and 5.22×10-17 cm3·molecule-1·s-1, respectively, generally in agreement with those fitted by the model.     

Direct ab initio dynamics calculations of the rate constants for the reaction of CHF2CF2OCH3 with Cl

A dual‐level direct dynamics method is employed to reveal the dynamical properties of the reaction of CHF₂CF₂OCH₃ (HFE‐254pc) with Cl atoms. The optimized geometries and frequencies of the stationary points and the minimum energy path (MEP) are calculated at the B3LYP/6‐311G(d,p) level by using GAUSSIAN 98 program package, and energetic information is further refined by the G3(MP2) method. Two H‐abstraction channels have been identified. For the reactant CHF₂CF₂OCH₃ and the two products, CHF₂CF₂OCH₂ and CF₂CF₂OCH₃, the standard enthalpies of formation are evaluated with the values of ?256.71 ± 0.88, ?207.79 ± 0.12, and ?233.43 ± 0.88 kcal/mol, respectively, via group‐balanced isodesmic reactions. The rate constants of the two reaction channels are evaluated by means of canonical variational transition‐state theory (CVT) including the small‐curvature tunneling (SCT) correction over a wide range of temperature from 200 to 2000 K. The calculated rate constants agree well with the experimental data, and the Arrhenius expressions for the title reaction are fitted and can be expressed as k₁ = 9.22 × 10^?19 T^2.06 exp(219/T), k₂ = 4.45 × 10^?14 T^0.90 exp(?2220/T), and k = 4.71 × 10^?22 T^3.20) exp(543/T) cm³ molecule^?1 s^?1. Our results indicate that H‐abstraction from ? CH₃ group is the main reaction pathway in the lower temperature range, while H‐abstraction from ? CHF₂ group becomes more competitive in the higher temperature range. © 2007 Wiley Periodicals, Inc. 39: 221–230, 2007     

Radical scavenging reactions of chlorogenic acid: A pulse radiolysis study

At near neutral pH (approx. 5.5), the OH-adduct of chlorogenic acid (CGA), formed on pulse radiolysis of N₂O-saturated aqueous CGA solutions (λ _max = 400 and 450 nm) with k = 9 × 10⁹ dm³ mol⁻¹ s⁻¹, rapidly eliminates water (k = 1 × 10³ s⁻¹) to give a resonance-stabilized phenoxyl type of radical. Oxygen rapidly adds to the OH-adduct of CGA (pH 5.5) to form a peroxyl type of radical (k = 6 × 10⁷ dm³ mol⁻¹ s⁻¹). At pH 10.5, where both the hydroxyl groups of CGA are deprotonated, the rate of reaction of · OH radicals with CGA was essentially the same as at pH 5.5, although there was a marked shift in the absorption maximum to approx. 500 nm. The CGA phenoxyl radical formed with more specific one-electron oxidants, viz., Br ₂ ^·− and N ₃ ^· radicals show an absorption maximum at 385 and 500 nm, k ranging from 1–5.5 × 10⁹ dm³ mol⁻¹ s⁻¹. Reactions of other one-electron oxidants, viz., NO ₂ ^· , NO^· and CCl₃OO^· radicals, are also discussed. Repair rates of thymidine, cytidine and guanosine radicals generated pulse radiolytically at pH 9.5 by CGA are in the range of (0.7–3) × 10⁹ dm³ mol⁻¹ s⁻¹.     

Determination of the rate constants for the reaction Fe + O<Subscript>2</Subscript> = FeO + O in the forward and reverse directions

The results of our experimental studies and an analysis of the published data on the rate constant for the reaction Fe + O₂ = FeO + O in the forward (I) and reverse (−I) direction are reported. The data obtained in this work are described by the expressions k ₁ = 6.2 × 10¹⁴exp(−11100 K/T) cm³ mol⁻¹ s⁻¹ and k ₋₁ = 6.0 × 10¹³exp(−588 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K). The generalized expressions for the temperature dependences of these rate constants derived by combining our results with the literature data can be presented as k ₁ = 9.4 × 10¹⁴(T/1000)^0.022exp(−11224 K/T) cm³ mol⁻¹ s⁻¹ (T = 1500–2500 K) and k ₋₁ = 1.8 × 10¹⁴(1000/T)^0.37exp(−367 K/T) cm³ mol⁻¹ s⁻¹ (T = 200–2500 K).     

Decomposition Mechanism of Fluorinated Compounds in Water Plasmas Generated Under Atmospheric Pressure

Decomposition mechanism of HFC-134a, HFC-32, and CF₄ in water plasmas at atmospheric pressure has been investigated. The decomposition efficiency of 99.9% can be obtained up to 3.17 mol kWh⁻¹ of the ratio of hydrofluorocarbon (HFC) feed rate to the arc power and 1.89 mol kWh⁻¹ of the ratio of perfluorocarbon (PFC) feed rate to the arc power. The species such as H₂, CO, CO₂, CH₄, and CF₄ were detected from the effluent gas of both PFC and HFC decomposition. However, CH₂F₂ and CHF₃ were observed only in the case of HFC decomposition. The HFC and PFC decomposition generate CH₂F, CHF_{x (x:1–2)}, and CF_{y (y:1–3)} radicals, then those radicals were subsequently oxidized by oxygen, leading to CO and CO₂ generation in the excess oxygen condition. However, when there is insufficient oxygen available, those radicals were easily recombined with fluorine to form by-product such as CH₂F₂, CHF₃, and CF₄.     

1,1,1,3,3,-pentafluorobutane (HFC-365mfc): atmospheric degradation and contribution to radiative forcing

The rate constant for the reaction of the hydroxyl radical with 1,1,1,3,3-pentafluorobutane (HFC-365mfc) has been determined over the temperature range 278–323K using a relative rate technique. The results provide a value of k(OH+CF₃CH₂CF₂CH₃)=2.0×10⁻¹²exp(−1750±400/T) cm³ molecule⁻¹ s⁻¹ based on k(OH+CH₃CCl₃)=1.8×10⁻¹² exp (−1550±150/T) cm³ molecule⁻¹ s⁻¹ for the rate constant of the reference reaction. Assuming the major atmospheric removal process is via reaction with OH in the troposphere, the rate constant data from this work gives an estimate of 10.8 years for the tropospheric lifetime of HFC-365mfc. The overall atmospheric lifetime obtained by taking into account a minor contribution from degradation in the stratosphere, is estimated to be 10.2 years. The rate constant for the reaction of Cl atoms with 1,1,1,3,3-pentafluorobutane was also determined at 298±2 K using the relative rate method, k(Cl+CF₃CH₂CF₂CH₃)=(1.1±0.3)×10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. The chlorine initiated photooxidation of CF₃CH₂CF₂CH₃ was investigated from 273–330 K and as a function of O₂ pressure at 1 atmosphere total pressure using Fourier transform infrared spectroscopy. Under all conditions the major carbon-containing products were CF₂O and CO₂, with smaller amounts of CF₃O₃CF₃. In order to ascertain the relative importance of hydrogen abstraction from the (SINGLE BOND)CH₂(SINGLE BOND) and (SINGLE BOND)CH₃ groups in CF₃CH₂CF₂CH₃, rate constants for the reaction of OH radicals and Cl atoms with the structurally similar compounds CF₃CH₂CCl₂F and CF₃CH₂CF₃ were also determined at 298 K k(OH+CF₃CH₂CCl₂F)=(8±3)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(OH+CF₃CH₂CF₃)=(3.5±1.5)×10⁻¹⁶ cm³ molecule⁻¹ s⁻¹; k(Cl+CF₃CH₂CCl₂F)=(3.5±1.5)×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹]; k(Cl+CF₃CH₂CF₃)<1×10⁻¹⁷ cm³ molecule⁻¹ s⁻¹. The results indicate that the most probable site for H-atom abstraction from CF₃CH₂CF₂CH₃ is the methyl group and that the formation of carbonyl compounds containing more than a single carbon atom will be negligible under atmospheric conditions, carbonyl difluoride and carbon dioxide being the main degradation products. Finally, accurate infrared absorption cross-sections have been measured for CF₃CH₂CF₂CH₃, and jointly used with the calculated overall atmospheric lifetime of 10.2 years, in the NCAR chemical-radiative model, to determine the radiative forcing of climate by this CFC alternative. The steady-state Halocarbon Global Warming Potential, relative to CFC-11, is 0.17. The Global Warming Potentials relative to CO₂ are found to be 2210, 790, and 250, for integration time-horizons of 20, 100, and 500 years, respectively. © 1997 John Wiley & Sons, Inc.     

Rate constants and Arrhenius parameters for the reactions of Cl atoms with the halogenated ethers: CF3CH2OCHF2, CF3CHClOCHF2, and CF3CH2OCClF2

Rate constants have been determined for the reactions of Cl atoms with the halogenated ethers CF₃CH₂OCHF₂, CF₃CHClOCHF₂, and CF₃CH₂OCClF₂ using a relative‐rate technique. Chlorine atoms were generated by continuous photolysis of Cl₂ in a mixture containing the ether and CD₄. Changes in the concentrations of these two species were measured via changes in their infrared absorption spectra observed with a Fourier transform infrared (FTIR) spectrometer. Relative‐rate constants were converted to absolute values using the previously measured rate constants for the reaction, Cl + CD₄ → DCl + CD₃. Experiments were carried out at 295, 323, and 363 K, yielding the following Arrhenius expressions for the rate constants within this range of temperature:Cl + CF₃CH₂OCHF₂: k = (5.1₅ ± 0.7) × 10⁻¹² exp(−1830 ± 410 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CHClOCHF₂: k = (1.6 ± 0.2) × 10⁻¹¹ exp(−2450 ± 250 K/T) cm³ molecule⁻¹ s⁻¹ Cl + CF₃CH₂OCClF₂: k = (9.6 ± 0.4) × 10⁻¹² exp(−2390 ± 190 K/T) cm³ molecule⁻¹ s⁻¹ The results are compared with those obtained previously for the reactions of Cl atoms with other halogenated methyl ethyl ethers. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 165–172, 2001     

Kinetics of Cl(2P) reactions with CF3CHCl2, CF3CHFCl,and CH3CFCl2

The rate coefficients for the removal of Cl atoms by reaction with three HCFCs, CF₃CHCl₂ (HCFC-123), CF₃CHFCl (HCFC-124), and CH₃CFCl₂ (HCFC 141b), were measured as a function of temperature between 276 and 397 K. CH₃CF₂Cl (HCFC-142b) was studied only at 298 K. The Arrhenius expressions obtained are: k₁ = (3.94 ± 0.84)× 10^?12 exp[?(1740 ± 100)/T] cm³ molecule^?1 s^?1 for CF₃CHCl₂ (HCFC 123); k₂ = (1.16 ± 0.41) × 10^?12 exp[?(1800 ± 150)/T] cm³ molecule^?1 s^?1 for CF₃CHFCl (HCFC 124); and k₃ = (1.6 ± 1.1) × 10^?12 exp[?(1800 ± 500)/T] cm³ molecule^?1 s^?1 for CH₃CFCl₂ (HCFC 141b). In case of HCFC 141b, non-Arrhenius behavior was observed at temperatures above ca. 350 K and is attributed to the thermal decomposition of CH₂CFCl₂ product into Cl + CH₂CFCl. In case of HCFC-142b, only an upper limit for the 298 K value of the rate coefficient was obtained. The atmospheric significance of these results are discussed. © 1993 John Wiley & Sons, Inc.     

New technique for generating high concentrations of gaseous OH radicals in relative rate measurements

We have developed a technique for generating high concentrations of gaseous OH radicals in a reaction chamber. The technique, which involves the UV photolysis of O₃ in the presence of water vapor, was used in combination with the relative rate method to obtain rate constants for reactions of OH radicals with selected species. A key improvement of the technique is that an O₃/O₂ (3%) gas mixture is continuously introduced into the reaction chamber, during the UV irradiation period. An important feature is that a high concentration of OH radicals [(0.53–1.2) × 10¹¹ radicals cm^?3] can be produced during the irradiation in continuous, steady‐state experiment. Using the new technique in conjunction with the relative rate method, we obtained the rate constant for the reaction of CHF₃ (HFC‐23) with OH radicals, k₁. We obtained k₁(298 K) = (3.32 ± 0.20) × 10^?16 and determined the temperature dependence of k₁ to be (0.48 ± 0.13) × 10^?12 exp[?(2180 ± 100)/T] cm³ molecule^?1 s^?1 at 253–328 K using CHF₂CF₃ (HFC‐125) and CHF₂Cl (HCFC‐22) as reference compounds in CHF₃–reference–H₂O gas mixtures. The value of k₁ obtained in this study is in agreement with previous measurements of k₁. This result confirms that our technique for generating OH radicals is suitable for obtaining OH radical reaction rate constants of ～10^?16 cm³ molecule^?1 s^?1, provided the rate constants do not depend on pressure. In addition, it also needed to examine whether the reactions of sample and reference compound with O₃ interfere the measurement when selecting this technique. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 317–325, 2003