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1.
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.  相似文献   

2.
The reactions of CH3 radicals with O(3P) and O2 have been studied at 295 K in a gas flow reactor sampled by a mass spectrometer. For the reaction between CH3 and O, conditions were such that [O] » [CH3] and the methyl radicals decayed under pseudo-first-order conditions giving a rate coefficient of (1.14 ± 0.29) × 10?10 cm3/s. The reaction between CH3 and O2 was studied in separate experiments in which CH3 decayed under pseudo-first-order conditions. In this case, the rate coefficient obtained increased with increasing concentration of the helium carrier gas. This was varied over the range of 2.5–25 × 1016 cm?3, resulting in values for the apparent two-body rate coefficient ranging from 1 × 10?14 to 5.2 × 10?14 cm3/s. No evidence was found for the production of HCHO by a direct two-body process involving CH3 + O2, and an upper limit of 3 × 10?16 cm3/s was placed on the rate coefficient for this reaction. The experimental results for the apparent two-body rate coefficient exhibit the curvature one would expect for an association reaction in the fall-off region. Calculations used to extrapolate these measurements to the low-pressure limit yield a value for k0 of (3.4 ± 1.1) × 10?31 cm6/s, which is more than a factor of 2 higher than previous estimates.  相似文献   

3.
Rate coefficients, k, and ClO radical product yields, Y, for the gas‐phase reaction of O(1D) with CClF2CCl2F (CFC‐113) (k2), CCl3CF3 (CFC‐113a) (k3), CClF2CClF2 (CFC‐114) (k4), and CCl2FCF3 (CFC‐114a) (k5) at 296 K are reported. Rate coefficients for the loss of O(1D) were measured using a competitive reaction technique, with n‐butane (n‐C4H10) as the reference reactant, employing pulsed laser photolysis production of O(1D) combined with laser‐induced fluorescence detection of the OH radical temporal profile. Rate coefficients were measured to be k2 = (2.33 ± 0.40) × 10?10 cm3 molecule?1 s?1, k3 = (2.61 ± 0.40) × 10?10 cm3 molecule?1 s?1, k4 = (1.42 ± 0.25) × 10?10 cm3 molecule?1 s?1, and k5 = (1.62 ± 0.30) × 10?10 cm3 molecule?1 s?1. ClO radical product yields for reactions (2)–(5) were measured using pulsed laser photolysis combined with cavity ring‐down spectroscopy to be 0.80 ± 0.10, 0.79 ± 0.10, 0.85 ± 0.12, and 0.79 ± 0.10, respectively. The quoted errors in k and Y are at the 2σ (95% confidence) level and include estimated systematic errors. © 2011 Wiley Periodicals, Inc.
  • 1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America
  • Int J Chem Kinet 43: 393–401, 2011  相似文献   

    4.
    The rate coefficient for the reaction of CCl3 radicals with ozone has been measured at 303 ± 2 K. The CCl3 radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl3 concentration was monitored with a photoionization mass spectrometer. Addition of the O3–O2 mixture to this system caused a decay of the CCl3 concentration because of the reactions of CCl3 + O3 → products (5) and CCl3 + O2 → products (4). The decay of signals from the CCl3 radical was measured in the presence and absence of ozone. In the absence of ozone, the O3–O2 mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl3 + O2 could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10?13 cm3 molecule?1 s?1 and was also found to be independent of the total pressure (253–880 Pa of N2). This result shows that the reaction of CCl3 with O3 cannot compete with its reaction with O2 in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003  相似文献   

    5.
    The recombination reaction O + O2 → O3 was studied by laser flash photolysis of pure O2 in the pressure range 3–20 atm, and of N2O? O2 mixtures in the bath gases Ar, N2, (CO2, and SF6) in the pressure range 3–200 atm. Fall-off curves of the reaction have been derived. Low-pressure rate coefficients were found to agree well with literature data. A high-pressure rate coefficient of k = (2.8 ± 1.0) × 10?12 cm3 molecule?1 s?1 was obtained by extrapolation.  相似文献   

    6.
    The reaction between C2H5 and O2 at 295 K has been studied with a flow reactor sampled by a mass spectrometer. With helium as the carrier gas the rate coefficient was found to increase from (1.2 ± 0.3) × 10?12 to (3.6 ± 0.9) × 10?12 cm3/s as [He] was increased from 2 × 1016 to 3.4 × 1017 cm?3. The importance of has been determined from a knowledge of the initial C2H5 concentration together with a measurement of the C2H4 produced in reaction (5). F, the fraction of the C2H5 radicals removed by path (5), was found to decrease from 0.15 to 0.06 as [He] increased from 2 × 1016 to 3.4 × 1017 cm?3. The rate coefficient for reaction (5) was found to be independent of [He] and to have a value of (2.1 ± 0.5) × 10?13 cm3/s. The variation in F reflects the fact that k1b increases as [He] increases. These observations are taken as evidence for a direct mechanism for C2H4 production and a collision-stabilized route for C2H5O2 formation. Calculations indicate that the high-pressure limit for reaction (1b) is ~4.4 × 10?12 cm3/s and that in the polluted troposphere the branching ratio for reactions (1b) and (5) will be ~l20.  相似文献   

    7.
    The rate constant of the reaction between CCl2 radicals and HCl was experimentally determined. The CCl2 radicals were obtained by infrared multiphoton dissociation of CDCl3. The time dependence of the CCl2 radicals' concentration in the presence of HCl was determined by laser‐induced fluorescence. The experimental conditions allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4 and to the reaction with HCl to form CHCl3. The rate constant for the self‐recombination reaction was determined to be in the high‐pressure regime. The value obtained at 300 K was (5.7 ± 0.1) × 10?13 cm3 molecule?1 s?1, whereas the value of the rate constant measured for the reaction with HCl was (2.7 ± 0.1) × 10?14 cm3 molecule?1 s?1.  相似文献   

    8.
    Rate constants for the reactions of O3 and OH radicals with furan and thiophene have been determined at 298 ± 2 K. The rate constants obtained for the O3 reactions were (2.42 ± 0.28) × 10?18 cm3/molec·s for furan and <6 ×10?20 cm3/molec·s for thiophene. The rate constants for the OH radical reactions, relative to a rate constant for the reaction of OH radicals with n-hexane of (5.70 ± 0.09) × 10?12 cm3/molec·s, were determined to be (4.01 ± 0.30) × 10?11 cm3/molec·s for furan and (9.58 ± 0.38) × 10?12 cm3/molec·s for thiophene. There are to date no reported rate constant data for the reactions of OH radicals with furan and thiophene or for the reaction of O3 with furan. The data are compared and discussed with respect to those for other alkenes, dialkenes, and heteroatom containing organics.  相似文献   

    9.
    Rate constants for the gas-phase reactions of the four oxygenated biogenic organic compounds cis-3-hexen-1-ol, cis-3-hexenylacetate, trans-2-hexenal, and linalool with OH radicals, NO3 radicals, and O3 have been determined at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm3 molecule?1 s?1 units): cis-3-hexen-1-ol: (1.08 ± 0.22) × 10?10 for reaction with the OH radical; (2.72 ± 0.83) × 10?13 for reaction with the NO3 radical; and (6.4 ± 1.7) × 10?17 for reaction with O3; cis-3-hexenylacetate: (7.84 ± 1.64) × 10?11 for reaction with the OH radical; (2.46 ± 0.75) × 10?13 for reaction with the NO3 radical; and (5.4 ± 1.4) × 10?17 for reaction with O3; trans-2-hexenal: (4.41 ± 0.94) × 10?11 for reaction with the OH radical; (1.21 ± 0.44) × 10?14 for reaction with the NO3 radical; and (2.0 ± 1.0) × 10?18 for reaction with O3; and linalool: (1.59 ± 0.40) × 10?10 for reaction with the OH radical; (1.12 ± 0.40) × 10?11 for reaction with the NO3 radical; and (4.3 ± 1.6) × 10?16 for reaction with O3. Combining these rate constants with estimated ambient tropospheric concentrations of OH radicals, NO3 radicals, and O3 results in calculated tropospheric lifetimes of these oxygenated organic compounds of a few hours. © 1995 John Wiley & Sons, Inc.  相似文献   

    10.
    An experimental setup that coupled IR multiple‐photon dissociation (IRMPD) and laser‐induced fluorescence (LIF) techniques was implemented to study the kinetics of the recombination reaction of dichlorocarbene radicals, CCl2, in an Ar bath. The CCl2 radicals were generated by IRMPD of CDCl3. The time dependence of the CCl2 radicals’ concentration in the presence of Ar was determined by LIF. The experimental conditions achieved allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C2Cl4. The rate constant for this reaction was determined in both the falloff and the high‐pressure regimes at room temperature. The values obtained were k0 = (2.23 ± 0.89) × 10?29 cm6 molecules?2 s?1 and k = (6.73 ± 0.23) × 10?13 cm3 molecules?1 s?1, respectively.  相似文献   

    11.
    Collisional deactivation of I(2P1/2) by the title compounds was investigated through the use of the time-resolved atomic absorption of excited iodine atoms at 206.2 nm. Rate constants for atomic spin-orbit relaxation by CH3Cl, CH2Cl2, CHCl3, CCl3F, and CCl4 are 3.1±0.3×10−13, 1.28±0.08×10−13, 5.7±0.3×10−14, 3.9±0.4×10−15, and 2.3±0.3×10−15cm3 molecule−1 s−1, respectively, at room temperature (298 K). The higher efficiency observed for relaxation by CH3Cl, CH2Cl2, and CHCl3 reveals a contribution in the deactivation process of the first overtone corresponding to the C(SINGLEBOND)H stretching of the deactivating molecule (which lies close to 7603 cm−1) as well as the number of the contributing modes and certain molecular properties such as the dipole moment. It is believed that, for these molecules, a quasi-resonant (E-v,r,t) energy transfer mechanism operates. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 799–803, 1998  相似文献   

    12.
    The kinetics of the atmospherically important gas-phase reactions of acenaphthene and acenaphthylene with OH and NO3 radicals, O3 and N2O5 have been investigated at 296 ± 2 K. In addition, rate constants have been determined for the reactions of OH and NO3 radicals with tetralin and styrene, and for the reactions of NO3 radicals and/or N2O5 with naphthalene, 1- and 2-methylnaphthalene, 2,3-dimethylnaphthalene, toluene, toluene-α,α,α-d3 and toluene-d8. The rate constants obtained (in cm3 molecule?1 s?1 units) at 296 ± 2 K were: for the reactions of O3; acenaphthene, <5 × 10?19 and acenaphthylene, ca. 5.5 × 10?16; for the OH radical reactions (determined using a relative rate method); acenaphthene, (1.03 ± 0.13) × 10?10; acenaphthylene, (1.10 ± 0.11) × 10?10; tetralin, (3.43 ± 0.06) × 10?11 and styrene, (5.87 ± 0.15) × 10?11; for the reactions of NO3 (also determined using a relative rate method); acenaphthene, (4.6 ± 2.6) × 10?13; acenaphthylene, (5.4 ± 0.8) × 10?12; tetralin, (8.6 ± 1.3) × 10?15; styrene, (1.51 ± 0.20) × 10?13; toluene, (7.8 ± 1.5) × 10?17; toluene-α,α,α-d3, (3.8 ± 0.9) × 10?17 and toluene-d8, (3.4 ± 1.9) × 10?17. The aromatic compounds which were observed to react with N2O5 and the rate constants derived were (in cm3 molecule?1 s?1 units): acenaphthene, 5.5 × 10?17; naphthalene, 1.1 × 10?17; 1-methylnaphthalene, 2.3 × 10?17; 2-methylnaphthalene, 3.6 × 10?17 and 2,3-dimethylnaphthalene, 5.3 × 10?17. These data for naphthylene and the alkylnaphthalenes are in good agreement with our previous absolute and relative N2O5 reaction rate constants, and show that the NO3 radical reactions with aromatic compounds proceed by overall H-atom abstraction from substituent-XH bonds (where X = C or O), or by NO3 radical addition to unsaturated substituent groups while the N2O5 reactions only occur for aromatic compounds containing two or more fused six-membered aromatic rings.  相似文献   

    13.
    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 Ea 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; Fc = 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.  相似文献   

    14.
    Rate constants for the reactions of O3 and OH radicals with acetylene, propyne, and 1-butyne have been determined at room temperature. The rate constants obtained at 294 ± 2 K for the reactions of O3 with acetylene, propyne, and 1-butyne were (7.8 ± 1.2) × 10?21 cm3/molecule · s, (1.43 ± 0.15) × 10?20 cm3/molecule · s, and (1.97 ± 0.26) × 10?20 cm3/molecule · s, respectively. The rate constants at 298 ± 2 K and atmospheric pressure for the reactions with the OH radical, relative to a rate constant for the reaction of OH radicals with cyclohexane of 7.57 × 10?12 cm3/molecule · s, were determined to be (8.8 ± 1.4) × 10?13 cm3/molecule · s, (6.21 ± 0.31) × 10?12 cm3/molecule · s, and (8.25 ± 0.23) × 10?12 cm3/molecule · s for acetylene, propyne, and 1-butyne, respectively. These data are discussed and compared with the available literature rate constants.  相似文献   

    15.
    The rate constants for proton transfer from H3+ ions to N2, O2, and CO have been measured as function of hydrogen buffer gas partial pressure. The rate constant for proton transfer from H3+ to N2 shows a very large pressure dependence, increasing from 1.0 × 10?9 cm3/s at low H2 partial pressures to 1.7 × 10?9 cm3/s at high H2 partial pressures. The rate constants for proton transfer from H3+ to O2 and CO are constant with partial pressure of H2; giving values of 6.4 × 10?10 cm3/s and 1.7 × 10?9 cm3/s, respectively. The roles of excess vibrational energy in H3+ ions and of equilibrium between forward and back reaction are discussed. Back reaction is observed only for the reaction of H3+ ions with O2, and an equilibrium constant of K = 2.0 ± 0.4 at 298 K has been determined. From these data the proton affinity of O2 is deduced to be 0.47 ± 0.11 kcal/mole higher than that of H2.  相似文献   

    16.
    The kinetics of the reaction of O3 with the aromatic vicinal diols 1,2‐benzenediol, 3‐methyl‐1,2‐benzenediol, and 4‐methyl‐1,2‐benzenediol have been investigated using a relative rate technique. The rate coefficients were determined in a 1080‐L smog chamber at 298 K and 1 atm total pressure of synthetic air using propene and 1,3‐butadiene as reference compounds. The following O3 reaction rate coefficients (in units of cm3 molecule?1 s?1) have been obtained: k(1,2‐benzenediol) = (9.60 ± 1.12) × 10?18, k(3‐methyl‐1,2‐benzenediol) = (2.81 ± 0.23) × 10?17, k(4‐methyl‐1,2‐benzenediol) = (2.63 ± 0.34) × 10?17. Absolute measurements of the O3 rate coefficient have also been carried out by measuring the decay of the dihydroxy compound in an excess of O3. The results from these experiments are in good agreement with the relative determinations. Atmospheric implications are discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 223–230, 2003  相似文献   

    17.
    Rate constants for the gas-phase reactions of the biogenically emitted monoterpene β-phellandrene with OH and NO3 radicals and O3 have been measured at 297 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained were (in cm3 molecule?1 s?1 units): for reaction with the OH radical, (1.68 ± 0.41) × 10?10; for reaction with the NO3 radical, (7.96 ± 2.82) × 10?12; and for reaction with O3, (4.77 ± 1.23) × 10?17, where the error limits include the estimated uncertainties in the reference reaction rate constants. Using these rate constants, the lifetime of β-phellandrene in the lower troposphere due to reaction with these species is calculated to be in the range of ca. 1–8 h, with the OH radical reaction being expected to dominate over the O3 reaction as a loss process for β-phellandrene during daylight hours.  相似文献   

    18.
    Rate constants for the gas phase reactions of O3 and OH radicals with 1,3-cycloheptadiene, 1,3,5-cycloheptatriene, and cis- and trans-1,3,5-hexatriene and also of O3 with cis-2,trans-4-hexadiene and trans -2,trans -4-hexadiene have been determined at 294 ± 2 K. The rate constants determined for reaction with O3 were (in cm3 molecule-1s?1 units): 1,3-cycloheptadiene, (1.56 ± 0.21) × 10-16; 1,3,5-cycloheptatriene, (5.39 ± 0.78) × 10?17; 1,3,5-hexatriene, (2.62 ± 0.34) × 10?17; cis?2,trans-4-hexadiene, (3.14 ± 0.34) × 10?16; and trans ?2, trans -4-hexadiene, (3.74 ± 0.61) × 10?16; with the cis- and trans-1,3,5-hexatriene isomers reacting with essentially identical rate constants. The rate constants determined for reaction with OH radicals were (in cm3 molecule?1 s?1 units): 1,3-cycloheptadiene, (1.31 ± 0.04) × 10?10; 1,3,5-cycloheptatriene, (9.12 × 0.23) × 10?11; cis-1,3,5-hexatriene, (1.04 ± 0.07) × 10?10; and trans 1,3,5-hexatriene, (1.04 ± 0.17) × 10?10. These data, which are the first reported values for these di- and tri-alkenes, are discussed in the context of previously determined O3 and OH radical rate constants for alkenes and cycloalkenes.  相似文献   

    19.
    Azulene, which is isomeric with naphthalene, was studied to determine whether it behaves like a polycyclic aromatic hydrocarbon or an alkene in its gas-phase reactions with OH and NO3 radicals and O3. Using relative rate methods, rate constants for the reactions of azulene with OH and NO3 radicals and O3 of (2.73 ± 0.56) × 10?10 cm3 molecule?1 s?1, (3.9) × 10?10 cm3 molecule?1 s?1, and <7 × 10?17 cm3 molecule?1 s?1, respectively, were obtained at 298 ± 2 K. The observation that the NO3 radical reaction did not involve NO2 in the rate determining step indicates that azulene behaves more like an alkene than a polycyclic aromatic hydrocarbon in this reaction. No conclusive evidence for the formation of nitroazulene(s) from either the OH or NO3 radical-initiated reaction of azulene (in the presence of NOx) was obtained.  相似文献   

    20.
    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.  相似文献   

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