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     

Bond dissociation energies and radical heats of formation in CH3Cl,CH2Cl2, CH3Br,CH2Br2, CH2FCl,and CHFCl2

An analysis of thermochemical and kinetic data on the bromination of the halomethanes CH_4–nX_n (X = F, Cl, Br; n = 1–3), the two chlorofluoromethanes, CH₂FCl and CHFCl₂, and CH₄, shows that the recently reported heats of formation of the radicals CH₂Cl, CHCl₂, CHBr₂, and CFCl₂, and the C? H bond dissociation energies in the matching halomethanes are not compatible with the activation energies for the corresponding reverse reactions. From the observed trends in CH₄ and the other halomethanes, the following revised ΔH°_f,298 (R) values have been derived: ΔH°_f(CH₂Cl) = 29.1 ± 1.0, ΔH°_f(CHCl₂) = 23.5 ± 1.2, ΔH_f(CH₂Br) = 40.4 ± 1.0, ΔH°_f(CHBr₂) = 45.0 ± 2.2, and ΔH°_f(CFCl₂) = ?21.3 ± 2.4 kcal mol^?1. The previously unavailable radical heat of formation, ΔH°_f(CHFCl) = ?14.5 ± 2.4 kcal mol^?1 has also been deduced. These values are used with the heats of formation of the parent compounds from the literature to evaluate C? H and C? X bond dissociation energies in CH₃Cl, CH₂Cl₂, CH₃Br, CH₂Br₂, CH₂FCl, and CHFCl₂.     

Atmospheric Chemistry of CH3CH2OCH3: Kinetics and Mechanism of Reactions with Cl Atoms and OH Radicals

The atmospheric chemistry of methyl ethyl ether, CH₃CH₂OCH₃, was examined using FT‐IR/relative‐rate methods. Hydroxyl radical and chlorine atom rate coefficients of k (CH₃CH₂OCH₃+OH) = (7.53 ± 2.86) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and k (CH₃CH₂OCH₃+Cl) = (2.35 ± 0.43) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹ were determined (297 ± 2 K). The Cl rate coefficient determined here is 30% lower than the previous literature value. The atmospheric lifetime for CH₃CH₂OCH₃ is approximately 2 days. The chlorine atom–initiated oxidation of CH₃CH₂OCH₃ gives CH₃C(O)H (9 ± 2%), CH₃CH₂OC(O)H (29 ± 7%), CH₃OC(O)H (19 ± 7%), and CH₃C(O)OCH₃ (17 ± 7%). The IR absorption cross section for CH₃CH₂OCH₃ is (7.97 ± 0.40) × 10⁻¹⁷ cm molecule⁻¹ (1000–3100 cm⁻¹). CH₃CH₂OCH₃ has a negligible impact on the radiative forcing of climate.     

Kinetics of the reactions of CH3O with Cl and CIO

The kinetics of the reactions CH₃O + Cl → H₂CO + HCl (1) and CH₃O + ClO → H₂CO + HOCl (2) have been studied using the discharge-flow techniques. CH₃O was monitored by laser-induced fluorescence, whereas mass spectrometry was used for the detection or titration of other species. The rate constants obtained at 298 K are: k₁ = (1.9 ± 0.4) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and k₂ = (2.3 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. These data are useful to interpret the results of the studies of the reactions of CH₃O₂ with Cl and ClO which, at least partly, produce CH₃O radicals. © 1996 John Wiley & Sons, Inc.     

Kinetics of the reactions of Cl atoms with CH3Br and CH2Br2

The rate coefficients for the reactions of Cl atoms with CH₃Br, (k₁) and CH₂Br₂, (k₂) were measured as functions of temperature by generating Cl atoms via 308 nm laser photolysis of Cl₂ and measuring their temporal profiles via resonance fluorescence detection. The measured rate coefficients were: k₁ = (1.55 ± 0.18) × 10^?11 exp{(?1070 ± 50)/T} and k₂ = (6.37 ± 0.55) × 10^?12 exp{(?810 ± 50)/T} cm³ molecule^?1 s^?1. The possible interference of the reaction of CH₂Br product with Cl₂ in the measurement of k₁ was assessed from the temporal profiles of Cl at high concentrations of Cl₂ at 298 K. The rate coefficient at 298 K for the CH₂Br + Cl₂ reaction was derived to be (5.36 ± 0.56) × 10^?13 cm³ molecule^?1 s^?1. Based on the values of k₁ and k₂, it is deduced that global atmospheric lifetimes for CH₃Br and CH₂Br₂ are unlikely to be affected by loss via reaction with Cl atoms. In the marine boundary layer, the loss via reaction (1) may be significant if the Cl concentrations are high. If found to be true, the contribution from oceans to the overall CH₃Br budget may be less than what is currently assumed. © 1994 John Wiley & Sons, Inc.     

Kinetics of the reactions of chlorine atoms with CH3ONO and CH3ONO2

The kinetics of the reactions of Cl atoms with CH₃ONO and CH₃ONO₂ have been studied using relative rate techniques. In 700 Torr of nitrogen diluent at 295 ± 2K, k(Cl + CH₃ONO) = (2.1 ± 0.2) × 10⁻¹² and k(Cl + CH₃ONO₂) = (2.4 ± 0.2) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹. The result for k(Cl + CH₃ONO₂) is in good agreement with the literature data. The result for k(Cl + CH₃ONO) is a factor of 4.5 lower than that reported previously. It seems likely that in the previous study most of the loss of CH₃ONO which was attributed to reaction with Cl atoms was actually caused by photolysis leading to an overestimate of k(Cl + CH₃ONO). © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 357–359, 1999     

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.     

Temperature dependence of the reaction of NO with CFCl2CH2O2 and CH3CFClO2 radicals

The reaction of NO with the peroxy radical CFCl₂CH₂O₂, and with CH₃CFClO₂ was investigated at 8(SINGLEBOND)20 torr and 263(SINGLEBOND)321 K by UV flash photolysis of CFCl₂CH₃/O₂/NO gas mixtures. The kinetics were determined from observations of the growth rate of the CFCl₂CH₂O radical and the decay rate of NO by time-resolved mass spectrometry. The temperature dependence of the bimolecular rate coefficients, with their statistical uncertainties, can be expressed as (2.9 ± 0.7) e^(435±96)/T × 10⁻¹² cm³ molecule ⁻¹s⁻¹, or (1.3 ± 0.2) (T/300)^{&minus(1.5±0.2)} × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for NO + CFCl₂CH₂O₂, and (3.3 ± 0.6)e^(516±73)/T × 10⁻¹² cm³ molecule⁻¹ s⁻¹, or (2.0 ± 0.3) (T/300)^{&minus(1.8±0.3)} × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ for NO + CH₃CFClO₂. No pressure dependence of the rate coefficients could be detected over the 8(SINGLEBOND)20 torr range investigated. © 1996 John Wiley & Sons, Inc.     

FTIR study of the Cl- and Br-atom initiated oxidation of trichloroethylene

The Cl- and Br- initiated oxidations of CHCl(DOUBLEBOND)CCl₂ in 700 torr of air at 296 K have been studied using a Fourier transform infrared spectrometer. Rate constants k(Cl+CHCl(DOUBLEBOND)CCl₂)=(7.2±0.8)×10⁻¹¹ and k(Br+CHCl(DOUBLEBOND)CCl₂)=(1.1±0.4)×10⁻¹³ cm³ molecule⁻¹ s⁻¹ were determined using a relative rate technique with ethane and ethylene as references, respectively. The major products observed were CHXClC(O)Cl, (X=Cl or Br), CHClO, and CCl₂O. Combining results obtained for the Cl-initiated oxidation of CHCl₂(SINGLEBOND)CHCl₂, we deduced that Cl-addition on trichloroethylene occurs via channel 1a, Cl+CHCl(DOUBLEBOND)CCl₂→ CHCl₂(SINGLEBOND)CCl₂, (100±12)%. Self-reaction of the subsequently generated peroxy radicals CHCl₂(SINGLEBOND)CCl₂O₂ leads to CHCl₂CCl₂O radicals which were found to decompose via channel 8a, CHCl₂C(O)Cl+Cl, (91±11)% of the time, and channel 8b, CHCl₂+CCl₂O, (9±2)%. The reaction Br+CHCl(DOUBLEBOND)CCl₂→CHBrCl(SINGLEBOND)CCl₂ (17a) accounted for ≥(96±11)% of the total reaction. Decomposition of the CHBrCl(SINGLEBOND)CCl₂O radicals proceeds (≥93±11)% via CHBrClC(O)Cl+Cl. As part of this work, k(Cl+CHCl₂C(O)Cl)=(3.6±0.6)×10⁻¹⁴ and k(Cl+CHCl₂(SINGLEBOND)CHCl₂)=(1.9±0.2)×10⁻¹³ cm³ molecule⁻¹ s⁻¹ were measured. Errors reported above include statistical uncertainties (2σ) and estimated systematic uncertainties. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet: 29: 695–704, 1997.     

A kinetic study of the reaction of fluorine atoms with CH3F,CH3Cl,CH3Br,CF2H2, CO,CF3H,CF3CHCl2, CF3CH2F,CHF2CHF2, CF2ClCH3, CHF2CH3, and CF3CF2H at 295 ± 2 K

A variety of relative and absolute techniques have been used to measure the reactivity of fluorine atoms with a series of halogenated organic compounds and CO. The following rate constants were derived, in units of cm³ molecule^?1 s^?1: CH₃F, (3.7 ± 0.8) × 10^?11, CH₃Cl, (3.3 ± 0.7) × 10^?11; CH₃Br, (3.0 ± 0.7) × 10^?11; CF₂H₂, (4.3 ± 0.9) × 10^?12; CO, (5.5 ± 1.0) × 10^?13 (in 700 torr total pressure of N₂ diluent); CF₃H, (1.4 ± 0.4) × 10^?13; CF₃CCl₂H (HCFC-123), (1.2 ± 0.4) × 10^?12; CF₃CFH₂ (HFC-134a), (1.3 ± 0.3) × 10^?12, CHF₂CHF₂ (HFC-134), (1.0 ± 0.3) × 10^?12; CF₂ClCH₃ (HCFC-42b), (3.9 ± 0.9) × 10^?12, CF₂HCH₃ (HFC-152a), (1.7 ± 0.4) × 10^?11; and CF₃CF₂H (HFC-125), (3.5 ± 0.8) × 10^?13. Quoted errors are statistical uncertainties (2σ). For rate constants derived using relative rate techniques, an additional uncertainty has been added to account for potential systematic errors in the reference rate constants used. Experiments were performed at 295 ± 2 K. Results are discussed with respect to the previous literature data and to the interpretation of laboratory studies of the atmospheric chemistry of HCFCs and HFCs. © 1993 John Wiley & Sons, Inc.     

A study of the self reaction of CH2ClO2 and CHCl2O2 radicals at 298 K

A low‐pressure discharge‐flow system equipped with laser‐induced fluorescence (LIF) detection of NO₂ and resonance‐fluorescence detection of OH has been employed to study the self reactions CH₂ClO₂ + CH₂ClO₂ → products (1) and CHCl₂O₂ + CHCl₂O₂ → products (2), at T = 298 K and P = 1–3 Torr. Possible secondary reactions involving alkoxy radicals are identified. We report the phenomenological rate constants (k_obs) k_1obs = (4.1 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ k_2obs = (8.6 ± 0.2) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ and the rate constants derived from modelling the decay profiles for both peroxy radical systems, which takes into account the proposed secondary chemistry involving alkoxy radicals k₁ = (3.3 ± 0.7) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ k₂ = (7.0 ± 1.8) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ A possible mechanism for these self reactions is proposed and QRRK calculations are performed for reactions (1), (2) and the self‐reaction of CH₃O₂, CH₃O₂ + CH₃O₂ → products (3). These calculations, although only semiquantitative, go some way to explaining why both k₁ and k₂ are a factor of ten larger than k₃ and why, as suggested by the products of reaction (1) and (2), it seems that the favored reaction pathway is different from that followed by reaction (3). The atmospheric fate of the chlorinated peroxy species, and hence the impact of their precursors (CH₃Cl and CH₂Cl₂), in the troposphere are briefly discussed. HC(O)Cl is identified as a potentially important reservoir species produced from the photooxidation of these precursors. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 433–444, 1999     

Atmospheric chemistry of CCl2FCH2CF3 (HCFC-234fb): Kinetics and mechanism of reactions with Cl atoms and OH radicals

The atmospheric chemistry of CCl₂FCH₂CF₃ (HFCF-234fb) was examined using FT-IR/relative-rate methods. Hydroxyl radical and chlorine atom rate coefficients of k(CCl₂FCH₂CF₃+OH)= (2.9 ± 0.8) × 10⁻¹⁵ cm³ molecule^–1 s^–1 and k(CCl₂FCH₂CF₃+Cl)= (2.3 ± 0.6) × 10⁻¹⁷ cm³ molecule^–1 s^–1 were determined at 297 ± 2 K. The OH rate coefficient determined here is two times higher than the previous literature value. The atmospheric lifetime for CCl₂FCH₂CF₃ with respect to reaction with OH radicals is approximately 21 years using the OH rate coefficient determined in this work, estimated Arrhenius parameters and scaling it to the atmospheric lifetime of CH₃CCl₃. The chlorine atom initiated oxidation of CCl₂FCH₂CF₃ gives C(O)F₂ and C(O)ClF as stable secondary products. The halogenated carbon balance is close to 80% in our system. The integrated IR absorption cross-section for CCl₂FCH₂CF₃ is 1.87 × 10⁻¹⁶ cm molecule⁻¹ (600–1600 cm⁻¹) and the radiative efficiency was calculated to 0.26 W m⁻² ppb¹. A 100-year Global Warming Potential (GWP) of 1460 was determined, accounting for an estimated stratospheric lifetime of 58 years and using a lifetime-corrected radiative efficiency estimation.     

Kinetics of the reactions of CCl3 with O and O2 and of CCl3O2 with NO at 295 K

The reactions of CCl₃ with O(³P) and O₂ and those of CCl₃O₂ with NO have been studied at 295 K using discharge flow methods with helium as the bath gas. The rate coefficient for the reaction of CCl₃ with O was found to be (4.2 ± 0.6) × 10^?11 cm³/s and that for CCl₃O₂ with NO was (18.6 ± 2.8) × 10^?12 cm³/s with both coefficients independent of [He]. For reaction between CCl₃ and O₂ the rate coefficient was found to increase from 1.51 7times; 10^?14 cm³/s to 7.88 × 10^?14 cm³/s as the [He] increased from 3.5 × 10¹⁶ cm^?3 to 2.7 × 10¹⁷ cm^?3. There was no evidence for a direct two-body reaction, and it is concluded that the only product of this reaction is CCl₃O₂. Examination of these results for CCl₃ + O₂ in terms of current simplified falloff treatment suggests that the high-pressure limit for this reaction is ～ 2.5 × 10^?12 cm³/s, which may be compared with a direct measurement of the high-pressure limit of 5 × 10^?12 cm³/s. A value of (5.8 ± 0.6) × 10^?31 cm⁶/s has been obtained for k₀, the coefficient in the low-pressure region. This value is compared with corresponding values found earlier for the (CH₃, O₂) and (CF₃, O₂) systems and with estimates based on unimolecular rate theory.     

Atmospheric chemistry of n‐CH3(CH2)xCN (x = 0–3): Kinetics and mechanisms

Smog chamber/Fourier transform infrared (FTIR) techniques were used to measure the kinetics of the reaction of n‐CH₃(CH₂)_xCN (x = 0–3) with Cl atoms and OH radicals: k(CH₃CN + Cl) = (1.04 ± 0.25) × 10⁻¹⁴, k(CH₃CH₂CN + Cl) = (9.20 ± 3.95) × 10⁻¹³, k(CH₃(CH₂)₂CN + Cl) = (2.03 ± 0.23) × 10⁻¹¹, k(CH₃(CH₂)₃CN + Cl) = (6.70 ± 0.67) × 10⁻¹¹, k(CH₃CN + OH) = (4.07 ± 1.21) × 10⁻¹⁴, k(CH₃CH₂CN + OH) = (1.24 ± 0.27) × 10⁻¹³, k(CH₃(CH₂)₂CN + OH) = (4.63 ± 0.99) × 10⁻¹³, and k(CH₃(CH₂)₃CN + OH) = (1.58 ± 0.38) × 10⁻¹² cm³ molecule⁻¹ s⁻¹ at a total pressure of 700 Torr of air or N₂ diluents at 296 ± 2 K. The atmospheric oxidation of alkyl nitriles proceeds through hydrogen abstraction leading to several carbonyl containing primary oxidation products. HC(O)CN, NCC(O)OONO₂, ClC(O)OONO₂, and HCN were identified as the main oxidation products from CH₃CN, whereas CH₃CH₂CN gives the products HC(O)CN, CH₃C(O)CN, NCC(O)OONO₂, and HCN. The oxidation of n‐CH₃(CH₂)_xCN (x = 2–3) leads to a range of oxygenated primary products. Based on the measured OH radical rate constants, the atmospheric lifetimes of n‐CH₃(CH₂)_xCN (x = 0–3) were estimated to be 284, 93, 25, and 7 days for x = 0,1, 2, and 3, respectively.     

Rate constant for the reaction of Cl with CHCl3

The rate constant for the reaction of Cl with CHCl₃ was measured relative to the Cl reaction with CH₄ and CH₃Cl using long path FTIR. The measured rate constant at 298 K and 1 atm total pressure was (1.21 ± 0.13) × 10⁻¹³ cm³ molecule ⁻¹s⁻¹ (2σ) about 60% larger than the currently recommended value (although within the large error bars). The implications of the Cl + CHCl₃ reaction for relative rate studies chloromethane reactivity, and tropospheric chemistry are discussed. © 1996 John Wiley & Sons, Inc.     

An FTIR study of the Cl atom-initiated oxidation of CH2Cl2 and CH3Cl

The Cl atom-initiated oxidation of CH₂Cl₂ and CH₃Cl was studied using the FTIR method in the photolysis of mixtures typically containing Cl₂ and the chlorinated methanes at 1 torr each in 700 torr air. The results obtained from product analysis were in general agreement with those reported by Sanhueza and Heicklen. The relative rate constant for the Cl atom reactions of CH₂Cl₂ and CH₃Cl was determined to be k(Cl +CH₃Cl)/k(Cl + CH₂Cl₂) = 1.31 ± 0.14 (2σ) at 298 ± 2 K.     

Flowtube reactor study of the association reactions of CHCl2 and CCl3 with O2 at low pressure

The new flowtube reactor employing dissociative electron attachment to produce radicals and high-pressure photoionization in the mass spectrometric detection of radicals is described. The system has been applied to a study of the association reactions of CHCl₂ and CCl₃ with O₂ in a great excess of helium at total densities below 10¹⁷ cm^?3 over the temperature range 286 to 332 K. Both reactions display a strong negative temperature coefficient. The results can be parameterized in the form k₀(CHCl₂ + O₂) = (4.3 ± 0.2) × 10^?31(T/300)^?6.7±0.7 cm⁶ s^?1, k₀(CCl₃ + O₂) = (2.7 ± 0.2) × 10^?31(T/300)^?8.7±1.0 cm⁶ s^?1. © 1994 John Wiley & Sons, Inc.     

A diode laser study of the Cl + CH3CO reaction

Real-time kinetic measurements are reported for the Cl + CH₃CO → CH₂CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10–200 torr and a temperature range of 215–353 K. Within experimental error the rate constant under these conditions is k_5a = (1.8 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹. We have also examined the Cl + CH₂CO reaction and found it to have a rate constant of k₆ = (2.5 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹ independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421–429, 1997.     

Oxidation of dimethyl ether: Absolute rate constants for the self reaction of CH3OCH2 radicals,the reaction of CH3OCH2 radicals with O2, and the thermal decomposition of CH3OCH2 radicals

The rate constant for the reaction of CH₃OCH₂ radicals with O₂ (reaction (1)) and the self reaction of CH₃OCH₂ radicals (reaction (5)) were measured using pulse radiolysis coupled with time resolved UV absorption spectroscopy. k₁ was studied at 296K over the pressure range 0.025–1 bar and in the temperature range 296–473K at 18 bar total pressure. Reaction (1) is known to proceed through the following mechanism: CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# → CH₂OCH₂O₂H^# → 2HCHO + OH (k_prod) CH₃OCH₂ + O₂ ↔ CH₃OCH₂O₂^# + M → CH₃OCH₂O₂ + M (k_RO2) k = k_RO2 + k_prod, where k_RO2 is the rate constant for peroxy radical production and k_prod is the rate constant for formaldehyde production. The k₁ values obtained at 296K together with the available literature values for k₁ determined at low pressures were fitted using a modified Lindemann mechanism and the following parameters were obtained: k_RO2,0 = (9.4 ± 4.2) × 10⁻³⁰ cm⁶ molecule⁻² s⁻¹, k_RO2,∞ = (1.14 ± 0.04) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_prod,0 = (6.0 ± 0.5) × 10⁻¹² cm³ molecule⁻¹ s⁻¹, where k_RO2,0 and k_RO2,∞ are the overall termolecular and bimolecular rate constants for formation of CH₃OCH₂O₂ radicals and k_prod,0 represents the bimolecular rate constant for the reaction of CH₃OCH₂ radicals with O₂ to yield formaldehyde in the limit of low pressure. k_RO2,∞ = (1.07 ± 0.08) × 10⁻¹¹ exp(−(46 ± 27)/T) cm³ molecule⁻¹ s⁻¹ was determined at 18 bar total pressure over the temperature range 296–473K. At 1 bar total pressure and 296K, k₅ = (4.1 ± 0.5) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ and at 18 bar total pressure over the temperature range 296–523K, k₅ = (4.7 ± 0.6) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹. As a part of this study the decay rate of CH₃OCH₂ radicals was used to study the thermal decomposition of CH₃OCH₂ radicals in the temperature range 573–666K at 18 bar total pressure. The observed decay rates of CH₃OCH₂ radicals were consistent with the literature value of k₂ = 1.6 × 10¹³exp(−12800/T)s⁻¹. The results are discussed in the context of dimethyl ether as an alternative diesel fuel. © 1997 John Wiley & Sons, Inc.     

Deactivation of I(52P1/2) by CF3I,CH3I,C2H5I,and CH4

The technique of laser photolysis of alkyl and perfluoroalkyl iodides at 266 nm followed by time-resolved detection of the 1.3-μm emission from I^*(²P_1/2) has been used to measure the rate constants for deactivation of I^* by CH₃I, C₂H₅I, CF₃I, and CH₄. The recommended values are (2.76± 0.22) × 10^?13, (2.85 ± 0.40) × 10^?13, (3.5 ± 0.5) × 10^?17, and (7.52 ± 0.12) × 10^?14, respectively, in units of cm³ molecule^?1 S^?1.