Recombination of methyl radicals at high temperatures

Hwang, S. M.; Rabinowitz, Martin J.; Gardiner, W. C.

doi:10.1016/0009-2614(93)89221-3

Cited by 38 publications

(38 citation statements)

References 18 publications

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“…Both Du et al [6] and Hwang, Wagner, and Wolff [ 5 ] are at variance with the present work, the former by greater than their published error limits, and the later within their error limits. Hwang, Rabinowitz, and Gardiner [7] are also in agreement. One possible reason for differences in the measured rate coefficients is the variation in the methyl absorption coefficients used in each of these studies.…”

Section: Resultssupporting

confidence: 79%

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

Davidson

Rosa

Chang

et al. 1995

Int J of Chemical Kinetics

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The methyl-methyl reaction was studied in a shock tube using uv narrowline laser absorption to measure time-varying concentration profiles of CH3. Methyl radicals were rapidly formed initially by pyrolysis of various precursors, azomethane, ethane, or methyl iodide, dilute in argon. The contributions of the various product channels, C~H I ; , C2H5 + H, CzH4 + Hz, and CH2 + CH4, were examined by varying reactant mixtures and temperature.The measured rate coefficients for recombination to CzHfi between 1200 and 1800 K are accurately fit using the unimolecular rate coefficients reported by Wagner and Wardlaw (1988). The rate coefficient for the CzH5 + H channel was found to be 2.4 (+0.5) X 10'" exp (-6480/Tj [cm3/mol-sl between 1570 and 1780 K, and is in agreement with the value reported by Frank and Braun-Unkhoff (1988). No evidence of a contribution by the C2H4 + Ha channel was found in ethane/methane/argon mixtures, although methyl profiles in these mixtures should be particularly sensitive to this channel. An upper limit of approximately 10l1 [cm3/mol-sl over the range 1700 to 2200 K was inferred for the rate coefficient of the CzH4 + Hz channel. Between 1800 and 2200 K, methyl radicals are also rapidly removed by CHs + H * 'CHz + Ha.In this temperature range, the reverse reaction was found to have a rate coefficient of 1.3 ( 2 0.3) X 1014 [cm3/mol-s], which is 1.8 times the room-temperature value. 0 1995 John Wiley & Sons, Inc.

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Section: Resultssupporting

confidence: 79%

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

Davidson

Rosa

Chang

et al. 1995

Int J of Chemical Kinetics

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“…Even though the recombination of CH 3 radicals to C 2 H 6 (R14) is well established over a large temperature and pressure range 76, some uncertainty remains in the temperature dependence of the high‐pressure limit. Shock tube experiments 90–92, supported by theoretical studies 93,94, indicate a slightly negative temperature dependence, whereas other data 95–97, including the preferred expression from Baulch et al 76, advocate a temperature independent high‐pressure limit.…”

Section: Detailed Kinetic Modelmentioning

confidence: 92%

“…h Enhanced third-body efficiencies: Ar = 0.7, H 2 = 2, H 2 O = 6, CH 4 = 3, CO = 1.5, CO 2 = 2, C 2 H 6 = 3. i Enhanced third-body efficiencies: H 2 = 2, H 2 O = 5, CO = 2, CO 2 = 3. dependence of the high-pressure limit. Shock tube experiments [90][91][92], supported by theoretical studies [93,94], indicate a slightly negative temperature dependence, whereas other data [95][96][97], including the preferred expression from Baulch et al [76], advocate a temperature independent high-pressure limit.…”

Section: Hydrocarbon Subsetmentioning

confidence: 98%

Experimental measurements and kinetic modeling of CH₄/O₂ and CH₄/C₂H₆/O₂ conversion at high pressure

Rasmussen

Jakobsen

Glarborg

2008

Int J of Chemical Kinetics

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A detailed chemical kinetic model for homogeneous combustion of the light hydrocarbon fuels CH4 and C2H6 in the intermediate temperature range roughly 500–1100 K, and pressures up to 100 bar has been developed and validated experimentally. Rate constants have been obtained from critical evaluation of data for individual elementary reactions reported in the literature with particular emphasis on the conditions relevant to the present work. The experiments, involving CH4/O2 and CH4/C2H6/O2 mixtures diluted in N2, have been carried out in a high‐pressure flow reactor at 600–900 K, 50–100 bar, and reaction stoichiometries ranging from very lean to fuel‐rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Finally, the mechanism was extended with a number of reactions important at high temperature and tested against data from shock tubes, laminar flames, and flow reactors. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 778–807, 2008

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“…The latter dynamical test employs UB3LYP/6-31G* density functional representations of the potential energy surface for both evaluations. The plethora of experimental data for this prototypical reaction, [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] especially near room temperature, makes this an ideal reaction for testing the full theoretical methodology. Meanwhile, comparisons with the large variety of prior theoretical studies 17,18, provide some indication of the appropriateness of their underlying assumptions.…”

Section: Introductionmentioning

confidence: 99%

Predictive theory for the combination kinetics of two alkyl radicals

Klippenstein

Georgievskii

Harding

2006

Phys. Chem. Chem. Phys.

214

272

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An ab initio transition state theory based procedure for accurately predicting the combination kinetics of two alkyl radicals is described. This procedure employs direct evaluations of the orientation dependent interaction energies at the CASPT2/cc-pvdz level within variable reaction coordinate transition state theory (VRC-TST). One-dimensional corrections to these energies are obtained from CAS+1+2/aug-cc-pvtz calculations for CH3 + CH3 along its combination reaction path. Direct CAS+1+2/aug-cc-pvtz calculations demonstrate that, at least for the purpose of predicting the kinetics, the corrected CASPT2/cc-pvdz potential energy surface is an accurate approximation to the CAS+1+2/aug-cc-pvtz surface. Furthermore, direct trajectory simulations, performed at the B3LYP/6-31G* level, indicate that there is little local recrossing of the optimal VRC transition state dividing surface. The corrected CASPT2/cc-pvdz potential is employed in obtaining direct VRC-TST kinetic predictions for the self and cross combinations of methyl, ethyl, iso-propyl, and tert-butyl radicals. Comparisons with experiment suggest that the present dynamically corrected VRC-TST approach provides quantitatively accurate predictions for the capture rate. Each additional methyl substituent adjacent to a radical site is found to reduce the rate coefficient by about a factor of two. In each instance, the rate coefficients are predicted to decrease quite substantially with increasing temperature, with the more sterically hindered reactants having a more rapid decrease. The simple geometric mean rule, relating the capture rate for the cross reaction to those for the self-reactions, is in remarkably good agreement with the more detailed predictions. With suitable generalizations the present approach should be applicable to a wide array of radical-radical combination reactions.

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Recombination of methyl radicals at high temperatures

Cited by 38 publications

References 18 publications

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

Experimental measurements and kinetic modeling of CH₄/O₂ and CH₄/C₂H₆/O₂ conversion at high pressure

Predictive theory for the combination kinetics of two alkyl radicals

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Recombination of methyl radicals at high temperatures

Cited by 38 publications

References 18 publications

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

A shock tube study of methyl‐methyl reactions between 1200 and 2400 K

Experimental measurements and kinetic modeling of CH4/O2 and CH4/C2H6/O2 conversion at high pressure

Predictive theory for the combination kinetics of two alkyl radicals

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Experimental measurements and kinetic modeling of CH₄/O₂ and CH₄/C₂H₆/O₂ conversion at high pressure