Kinetic investigations of the unimolecular decomposition of dimethylether behind shock waves

Fernandes, Ravi X.; Fittschen, Christa; Hippler, H.

doi:10.1007/s11144-009-5505-9

Cited by 14 publications

(20 citation statements)

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“…We also extend these ultra-dilute pseudo-first order studies to experiments with roughly the same [CH 3 OCH 3 ] 0 as Fernandes et al [9]. These higher concentration experiments expand our rate constant database for DME decomposition to lower-T, and allow for the determination of rate constants for H + CH 3 OCH 3 via the modeling of the temporal H-atom profiles.…”

Section: Introductionmentioning

confidence: 66%

“…In contrast, the present work uses a higher sensitivity H-atom ARAS detection scheme to minimize secondary reactions, and this allows determinations for absolute yields of products. The resonance light source used in this laboratory is unreversed, giving an increase of $5-10 in sensitivity over that used by Fernandes et al [9], who also used the ARAS technique but with a substantially reversed resonance light source [19]. As in earlier work [20], we show that this unreversed source allows experiments to be performed under pseudo-first order conditions; i.e., with no secondary reaction interferences.…”

Section: Introductionmentioning

confidence: 73%

“…The second set of experiments used more concentrated mixtures (5-10 ppm) that are similar to those from the recent H-ARAS study of Fernandes et al [9]. Under these conditions, secondary reactions begin to perturb the [H] profile, particularly the abstraction reaction,…”

Section: Low Temperature/more Concentrated Experimentsmentioning

confidence: 99%

“…In order to better characterize the high-temperature thermal decomposition rates, two recent studies have been carried out using shock tubes. The Fernandes et al [9] study used H-atom ARAS as the diagnostic for measuring rate coefficients for R1. By contrast, the Cook et al [10] study used mixtures of DME in excess O 2 with OH-absorption as the diagnostic.…”

Section: Introductionmentioning

confidence: 99%

“…Even the H-atom ARAS study of Fernandes et al [9], with the lowest initial DME concentrations of any published DME kinetics experiment, still used relatively large initial concentrations. As a result, one secondary reaction, namely H + CH 3 OCH 3 ?…”

Section: Introductionmentioning

confidence: 99%

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Roaming radicals in the thermal decomposition of dimethyl ether: Experiment and theory

Sivaramakrishnan

Michael

Wagner

et al. 2011

Combustion and Flame

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a b s t r a c tThe thermal dissociation of dimethyl ether has been studied with a combination of reflected shock tube experiments and ab initio dynamics simulations coupled with transition state theory based master equation calculations. The experiments use the extraordinary sensitivity provided by H-atom ARAS detection with an unreversed light source to measure both the total decomposition rate and the branching to radical products versus molecular products, with the molecular products arising predominantly through roaming according to the theoretical analysis. The experimental observations also provide a measure of the rate coefficient for H + CH 3 OCH 3 . An evaluation of the available experimental results for H + CH 3 OCH 3 can be expressed by a three parameter Arrhenius expression as, k ¼ 6:54 Â 10 À24 T 4:13 expðÀ896=TÞ cm 3 molecule À1 s À1 ð273 À 1465 KÞ The potential energy surface is explored with high level ab initio electronic structure theory. The dynamics of roaming versus radical formation is studied with a reduced dimensional trajectory approach. The requisite potential energy surface is obtained from an interpolative moving least squares fit to wide-ranging ab initio data for the long-range interactions between methyl and methoxy. The predicted roaming and radical micro-canonical fluxes are incorporated in a master equation treatment of the temperature and pressure dependence of the dissociation process. The tight (i.e., non-roaming) transition states leading to a variety of additional molecular fragments are also included in the master equation analysis, but are predicted to have a negligible contribution to product formation. The final theoretical results reliably reproduce the measured dissociation rate to radical products reported here and are well reproduced over the 500-2000 K temperature range and the 0.01-300 bar pressure range by the following modified Arrhenius parameters for the Troe falloff format: k 1;1 ðTÞ ¼ 2:33 Â 10 19 T À0:661 expðÀ42345=TÞ s À1 k 1;0 ðTÞ ¼ 2:86 Â 10 35 T À11:4 expðÀ46953=TÞ cm 3 molecule À1 s À1 F cent ðTÞ ¼ expðÀT=880ÞThe experimentally observed branching ratio of 0.19 ± 0.07 provides a direct measure of the contribution from the roaming radical mechanism. The theoretical analysis predicts a much smaller roaming contribution of 0.02.

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Section: Introductionmentioning

confidence: 66%

Section: Introductionmentioning

confidence: 73%

Section: Low Temperature/more Concentrated Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Roaming radicals in the thermal decomposition of dimethyl ether: Experiment and theory

Sivaramakrishnan

Michael

Wagner

et al. 2011

Combustion and Flame

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Systematic study on the hydrogen abstraction reactions from oxygenated compounds by H and HO₂

Oppata,

Shimokuri,

Miyoshi

2024

Int J of Chemical Kinetics

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To extend the rule‐based approach for hydrogen abstraction reactions from oxygenated compounds, a systematic investigation was performed to examine the reactivity of gas‐phase hydrogen abstraction reactions from alkyl groups (methyl and ethyl groups) bound to oxygen atoms in five types of oxygenated compounds (alcohols, ethers, formate esters, acetate esters, and carbonate esters) by H atoms and HO2 radicals comprehensively considering rotational conformers. Quantum chemical calculations were conducted at the CBS‐QB3 level for stationary points. Rate constants were determined employing conventional transition state theory (TST). For hydrogen abstraction reactions by H, the rotational conformer distribution partition function was employed to approximate partition functions, owing to the similarity in vibrational energy‐level structures among conformers. In hydrogen abstraction reactions by HO2, the vibrational structures of transition‐state (TS) conformers varied significantly due to the hydrogen bonding, leading to an inappropriate evaluation of rate constants when using the lowest‐energy conformer as a representative. Therefore, the rate constants were calculated by the multi‐structural TST. It was revealed that the differences in functional groups containing O atoms mainly affect the bond dissociation energies of the C–H bonds and the activation energies of hydrogen abstraction reactions only when the C atoms are adjacent to the O atoms. Additionally, it was found that hydrogen bonds formed in the TSs show minor effect on rate parameters for the overall rate constants, apart from the reduction of the pre‐exponential factors for the H‐abstraction reactions from the methylene position of ethyl groups. The comparison with the rate constants from previous studies showed reasonable results, indicating that the rate constants in this study, which thoroughly consider rotational conformers, can be the current best estimates.

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Hydrogen migration as a potential driving force in the thermal decomposition of dimethoxymethane: New insights from pyrolysis imaging photoelectron photoion coincidence spectroscopy and computations

Zhou

et al. 2020

Combustion and Flame

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Kinetic investigations of the unimolecular decomposition of dimethylether behind shock waves

Abstract: The thermal decomposition of dimethylether was studied behind reflected shock waves at total pressures of 0.3 -1.3 bar in the temperature range 1270 -1620 K using H-atom detection by Lyman-α resonance absorption spectroscopy at 121.6 nm.

Cited by 14 publications

References 20 publications

Roaming radicals in the thermal decomposition of dimethyl ether: Experiment and theory

Roaming radicals in the thermal decomposition of dimethyl ether: Experiment and theory

Systematic study on the hydrogen abstraction reactions from oxygenated compounds by H and HO₂

Hydrogen migration as a potential driving force in the thermal decomposition of dimethoxymethane: New insights from pyrolysis imaging photoelectron photoion coincidence spectroscopy and computations

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Kinetic investigations of the unimolecular decomposition of dimethylether behind shock waves

Abstract: The thermal decomposition of dimethylether was studied behind reflected shock waves at total pressures of 0.3 -1.3 bar in the temperature range 1270 -1620 K using H-atom detection by Lyman-α resonance absorption spectroscopy at 121.6 nm.

Cited by 14 publications

References 20 publications

Roaming radicals in the thermal decomposition of dimethyl ether: Experiment and theory

Roaming radicals in the thermal decomposition of dimethyl ether: Experiment and theory

Systematic study on the hydrogen abstraction reactions from oxygenated compounds by H and HO2

Hydrogen migration as a potential driving force in the thermal decomposition of dimethoxymethane: New insights from pyrolysis imaging photoelectron photoion coincidence spectroscopy and computations

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Systematic study on the hydrogen abstraction reactions from oxygenated compounds by H and HO₂