Reply to Comment on “Rate Constants for CH3 + O2 → CH3O + O at High Temperature and Evidence for H2CO + O2 → HCO + HO2”

Michael, J. V.; Kumaran, and S. S.; Su, M.‐C.

doi:10.1021/jp994495u

Cited by 7 publications

(9 citation statements)

References 33 publications

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“…These conditions are similar to those used by Hwang et al 5 who were careful to take boundary layer effects into account in determining total density and temperature. 7,8 It is clear from Figure 12 that the mechanism as presented does predict chain branching and is sufficient to test ignition delay experiments. We point out that the mechanism should only be used in the initial stages of reactions because it is not detailed enough to explain the chemistry occurring in the high conversion regime.…”

Section: Implications To Methane Combustionmentioning

confidence: 83%

“…The disagreement of rate constant values and the neglect of eq 1b prompted a comment from Eiteneer and Frenklach 6 and responses from Michael et al 7 and Hwang et al 8 Scire et al 9 and Hessler et al 10 have also indicated that their results cannot be explained without some significance for reaction 1b. The large spread in values for the branching ratio between eqs 1b and 1c, 3 along with the cited controversy, [6][7][8][9][10] motivated the recent shock tube study by Herbon et al 11 who used both O-atom ARAS and OH-radical electronic absorption detection methods to assess the branching ratio. Between 1590 and 2430 K, their results for eq 1c were in good agreement with Hwang et al 5 and were only 32% higher than those by Michael et al 4 They did however find that eq 1b was the major process over their temperature range.…”

Section: Introductionmentioning

confidence: 99%

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Reflected Shock Tube Studies of High-Temperature Rate Constants for CH₃ + O₂, H₂CO + O₂, and OH + O₂

et al. 2005

J. Phys. Chem. A

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The reflected shock tube technique with multipass absorption spectrometric detection of OH-radicals at 308 nm, corresponding to a total path length of approximately 2.8 m, has been used to study the reaction CH3 + O2 CH2O + OH. Experiments were performed between 1303 and 2272 K, using ppm quantities of CH3I (methyl source) and 5-10% O2, diluted with Kr as the bath gas at test pressures less than 1 atm. We have also reanalyzed our earlier ARAS measurements for the atomic channel (CH3 + O2 --> CH3O + O) and have compared both these results with other earlier studies to derive a rate expression of the Arrhenius form. The derived expressions, in units of cm3 molecule(-1) s(-1), are k = 3.11 x 10(-13) exp(-4953 K/T) over the T-range 1237-2430 K, for the OH-channel, and k = 1.253 x 10(-11) exp(-14241 K/T) over the T-range 1250-2430 K, for the O-atom channel. Since CH2O is a major product in both reactions, reliable rates for the reaction CH2O + O2 --> HCO + HO2 could be derived from [OH]t and [O]t experiments over the T-range 1587-2109 K. The combined linear least-squares fit result, k = 1.34 x 10(-8) exp(-26883 K/T) cm3 molecule(-1) s(-1), and a recent VTST calculation clearly overlap within the uncertainties in both studies. Finally, a high sensitivity for the reaction OH + O2 --> HO2 + O was noted at high temperature in the O-atom data set simulations. The values for this obtained by fitting the O-atom data sets at later times (approximately 1.2 ms) again follow the Arrhenius form, k = 2.56 x 10(-10) exp(-24145 K/T) cm3 molecule(-1) s(-1), over the T-range, 1950-2100 K.

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Section: Implications To Methane Combustionmentioning

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH₃ + O₂, H₂CO + O₂, and OH + O₂

et al. 2005

J. Phys. Chem. A

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“…Reactions – present three competitive channels for oxidation of CH 3 , the most stable alkyl radical appearing in many combustion processes . However, their relative importance appears controversial. − The channel R2 represents branching chain oxidation, important for radical reaction propagation . Mechanisms of R1 , starting from methyl radical and oxygen diatomic in the gas phase (and continuing to H 2 C(O)OH and CH(OH) 2 ), were reported by Cheung and Li .…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Study of CH₃ + O₂ Combustion Reaction System: Catalytic Effects of Additional CO₂ Molecule

Masunov

Wait²,

Vasu

2017

J. Phys. Chem. A

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The supercritical carbon dioxide diluent is used to control the temperature and to increase the efficiency in oxycombustion fossil fuel energy technology. It may affect the rates of combustion by altering mechanisms of chemical reactions, compared to the ones at low CO concentrations. Here, we investigate potential energy surfaces of the four elementary reactions in the CH + O reactive system in the presence of one CO molecule. In the case of reaction CH + O → CHO + OH (R1 channel), van der Waals (vdW) complex formation stabilizes the transition state and reduces the activation barrier by ∼2.2 kcal/mol. Alternatively, covalently bonded CO may form a six-membered ring transition state and reduce the activation barrier by ∼0.6 kcal/mol. In case of reaction CH + O → CHO + O (R2 channel), covalent participation of CO lowers the barrier for the rate limiting step by 3.9 kcal/mol. This is expected to accelerate the R2 process, important for the branching step of the radical chain reaction mechanism. For the reaction CH + O → CHO + HO (R3 channel) with covalent participation of CO, the activation barrier is lowered by 0.5 kcal/mol. The reaction CHO + OH → CHO + HO (R4 channel) involves hydrogen abstraction from formaldehyde by OH radical. Its barrier is reduced from 7.1 to 0.8 kcal/mol by formation of vdW complex with spectator CO. These new findings are expected to improve the kinetic reaction mechanism describing combustion processes in supercritical CO medium.

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“…In order to transform the measured absorbance (ABS) O to O-atom concentration, the O-atom photometer has to be calibrated. In previous studies, [O] was calibrated by applying two methods: (1) the thermal dissociation of N 2 O and (2) using the reaction H + O 2 → OH + O . In the second method, C 2 H 5 I was used as thermal precursor for H-atoms.…”

Section: Resultsmentioning

confidence: 99%

“…A reaction mechanism with well-established rate constants was utilized for determining (ABS) O against [O] formed in the H + O 2 reaction system. A curve-of-growth, Figure , was obtained by combining the two methods. , All data points were fitted by applying a second-order polynomial least-squares analysis giving [ O ] = 2.2108 × 10 10 + 8.7891 × 10 12 false( ABS false) normalO + 5.5278 × 10 12 false( ABS false) normalO 2 .25em atoms cm − 3 This function was then used to transform the measured (ABS) t for O 3 decomposition into [O] t . Figure shows a derived O-atom profile for the experiment shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

High Temperature Shock Tube Studies on the Thermal Decomposition of O₃and the Reaction of Dimethyl Carbonate with O-Atoms

2013

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The shock tube technique was used to study the thermal decomposition of ozone, O3, with a view to using this as a thermal precursor of O-atoms at high temperatures. The formation of O-atoms was measured behind reflected shock waves by using atomic resonance absorption spectrometry (ARAS). The experiments span a T-range, 819 K ≤ T ≤ 1166 K, at pressures 0.13 bar ≤ P ≤ 0.6 bar. Unimolecular rate theory provides an excellent representation of the falloff characteristics from the present and literature data on ozone decomposition at high temperatures. The present decomposition study on ozone permits its usage as a thermal source for O-atoms allowing measurements for, O + CH3OC(O)OCH3 → OH + CH3OC(O)OCH2 [A]. Reflected shock tube experiments monitoring the formation and decay of O-atoms were performed on reaction A using mixtures of O3 and CH3OC(O)OCH3, (DMC), in Kr bath gas over the T-range, 862 K ≤ T ≤ 1167 K, and pressure range, 0.15 bar ≤ P ≤ 0.33 bar. A detailed model was used to fit the O-atom temporal profile to obtain experimental rate constants for reaction A. Rate constants from the present experiments for O + DMC can be represented by the Arrhenius expression: kA(T) = 2.70 × 10(-11) exp(-2725 K/T) cm(3) molecule(-1) s(-1) (862-1167 K). Transition state theory calculations employing CCSD(T)/cc-pv∞z//M06-2X/cc-pvtz energetics and molecular properties for reaction A are in good agreement with the experimental rate constants. The theoretical rate constants can be well represented (to within ±10%) over the 500-2000 K temperature range by: kA(T) = 1.87 × 10(-20)T(2.924) exp(-2338 K/T) cm(3) molecule(-1) s(-1). The present study represents the first experimental measurement and theoretical study on this bimolecular reaction which is of relevance to the high temperature oxidation of DMC.

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Reply to Comment on “Rate Constants for CH₃ + O₂ → CH₃O + O at High Temperature and Evidence for H₂CO + O₂ → HCO + HO₂”

Cited by 7 publications

References 33 publications

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH₃ + O₂, H₂CO + O₂, and OH + O₂

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH₃ + O₂, H₂CO + O₂, and OH + O₂

Quantum Chemical Study of CH₃ + O₂ Combustion Reaction System: Catalytic Effects of Additional CO₂ Molecule

High Temperature Shock Tube Studies on the Thermal Decomposition of O₃and the Reaction of Dimethyl Carbonate with O-Atoms

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Reply to Comment on “Rate Constants for CH3 + O2 → CH3O + O at High Temperature and Evidence for H2CO + O2 → HCO + HO2”

Cited by 7 publications

References 33 publications

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH3 + O2, H2CO + O2, and OH + O2

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH3 + O2, H2CO + O2, and OH + O2

Quantum Chemical Study of CH3 + O2 Combustion Reaction System: Catalytic Effects of Additional CO2 Molecule

High Temperature Shock Tube Studies on the Thermal Decomposition of O3and the Reaction of Dimethyl Carbonate with O-Atoms

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Resources

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Reply to Comment on “Rate Constants for CH₃ + O₂ → CH₃O + O at High Temperature and Evidence for H₂CO + O₂ → HCO + HO₂”

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH₃ + O₂, H₂CO + O₂, and OH + O₂

Reflected Shock Tube Studies of High-Temperature Rate Constants for CH₃ + O₂, H₂CO + O₂, and OH + O₂

Quantum Chemical Study of CH₃ + O₂ Combustion Reaction System: Catalytic Effects of Additional CO₂ Molecule

High Temperature Shock Tube Studies on the Thermal Decomposition of O₃and the Reaction of Dimethyl Carbonate with O-Atoms