Hydrogen shift isomerizations in the kinetics of the second oxidation mechanism of alkane combustion. Reactions of the hydroperoxypentylperoxy OOQOOH radical

Xing, Lili; Bao, Junwei Lucas; Wang, Zhandong; Wang, Xuetao; Truhlar, Donald G.

doi:10.1016/j.combustflame.2018.07.013

Cited by 26 publications

(37 citation statements)

References 82 publications

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“…In our work on other reactive systems, we observed that this maximum arises at lower temperatures as the number of atoms in the involved molecules increases and is not particular of the system under investigation: it has been also described by other authors in the study of the hydrogen shift isomerization of oxygenated C 5 hydrocarbons. 37 …”

Section: Resultsmentioning

confidence: 99%

Collision Efficiency Parameter Influence on Pressure-Dependent Rate Constant Calculations Using the SS-QRRK Theory

2020

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The system-specific quantum Rice–Ramsperger–Kassel (SS-QRRK) theory ( J. Am. Chem. Soc. 2016 , 138 , 2690) is suitable to determine rate constants below the high-pressure limit. Its current implementation allows incorporating variational effects, multidimensional tunneling, and multistructural torsional anharmonicity in rate constant calculations. Master equation solvers offer a more rigorous approach to compute pressure-dependent rate constants, but several implementations available in the literature do not incorporate the aforementioned effects. However, the SS-QRRK theory coupled with a formulation of the modified strong collision model underestimates the value of unimolecular pressure-dependent rate constants in the high-temperature regime for reactions involving large molecules. This underestimation is a consequence of the definition for collision efficiency, which is part of the energy transfer model. Selection of the energy transfer model and its parameters constitutes a common issue in pressure-dependent calculations. To overcome this underestimation problem, we evaluated and implemented in a bespoke Python code two alternative definitions for the collision efficiency using the SS-QRRK theory and tested their performance by comparing the pressure-dependent rate constants with the Rice–Ramsperger–Kassel–Marcus/Master Equation (RRKM/ME) results. The modeled systems were the tautomerization of propen-2-ol and the decomposition of 1-propyl, 1-butyl, and 1-pentyl radicals. One of the tested definitions, which Dean et al. explicitly derived ( Z. Phys. Chem. 2000 , 214 , 1533), corrected the underestimation of the pressure-dependent rate constants and, in addition, qualitatively reproduced the trend of RRKM/ME data. Therefore, the used SS-QRRK theory with accurate definitions for the collision efficiency can yield results that are in agreement with those from more sophisticated methodologies such as RRKM/ME.

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Section: Resultsmentioning

confidence: 99%

Collision Efficiency Parameter Influence on Pressure-Dependent Rate Constant Calculations Using the SS-QRRK Theory

2020

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“…The reactants, transition states, and products in the studied mechanistic branches of the isoprene chemistry were characterized at the M06-2X and CCSD(T) levels of theory. The conformer space for each of these structures was characterized at the M06-2X/cc-pVDZ level of theory (Dunning, 1989;Zhao and Truhlar, 2008;Alecu et al, 2010;Bao et al, 2017), locating ∼ 24 000 distinguishable structures from ∼ 60 000 systematically generated starting geometries. The most relevant conformers (∼ 850 structures across all reactions examined) were then fully re-optimized at the M06-2X/aug-cc-pVTZ level of theory (Dunning, 1989).…”

Section: Quantum Chemical and Theoretical Kinetic Calculationsmentioning

confidence: 99%

“…The lower energy barriers of the effective aldehyde-Hmigration processes imply that the acyl radical tri-HPACYL is formed with a significantly lower energy content, 17-19 kcal mol −1 , than estimated by Peeters et al (2014), reducing the likelihood of chemically activated decomposition. Note that the H-migration reactions are typically found to be in the high-pressure limit (Miyoshi, 2012;Peeters et al, 2014;Xing et al, 2018;Møller et al, 2019), and multistep chemical activation does not contribute significantly. Furthermore, we found that the CO elimination barrier in tri-HPACYL-I, ∼ 8 kcal mol −1 (see Table S1), is higher than estimated by Peeters et al (2014) (≤ 7 kcal mol −1 ), further hampering prompt decomposition.…”

Section: Elimination Of Co From Tri-hydroperoxy Acyl Radicalsmentioning

confidence: 99%

Importance of isomerization reactions for OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

et al. 2020

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Abstract. Theoretical, laboratory, and chamber studies have shown fast regeneration of the hydroxyl radical (OH) in the photochemistry of isoprene, largely due to unimolecular reactions which were previously thought not to be important under atmospheric conditions. Based on early field measurements, nearly complete regeneration was hypothesized for a wide range of tropospheric conditions, including areas such as the rainforest where slow regeneration of OH radicals is expected due to low concentrations of nitric oxide (NO). In this work the OH regeneration in isoprene oxidation is directly quantified for the first time through experiments covering a wide range of atmospherically relevant NO levels (between 0.15 and 2 ppbv – parts per billion by volume) in the atmospheric simulation chamber SAPHIR. These conditions cover remote areas partially influenced by anthropogenic NO emissions, giving a regeneration efficiency of OH close to 1, and areas like the Amazonian rainforest with very low NO, resulting in a surprisingly high regeneration efficiency of 0.5, i.e. a factor of 2 to 3 higher than explainable in the absence of unimolecular reactions. The measured radical concentrations were compared to model calculations, and the best agreement was observed when at least 50 % of the total loss of isoprene peroxy radicals conformers (weighted by their abundance) occurs via isomerization reactions for NO lower than 0.2 ppbv. For these levels of NO, up to 50 % of the OH radicals are regenerated from the products of the 1,6 α-hydroxy-hydrogen shift (1,6-H shift) of Z-δ-RO2 radicals through the photolysis of an unsaturated hydroperoxy aldehyde (HPALD) and/or through the fast aldehydic hydrogen shift (rate constant ∼10 s−1 at 300 K) in di-hydroperoxy carbonyl peroxy radicals (di-HPCARP-RO2), depending on their relative yield. The agreement between all measured and modelled trace gases (hydroxyl, hydroperoxy, and organic peroxy radicals, carbon monoxide, and the sum of methyl vinyl ketone, methacrolein, and hydroxyl hydroperoxides) is nearly independent of the adopted yield of HPALD and di-HPCARP-RO2 as both degrade relatively fast (<1 h), forming the OH radical and CO among other products. Taking into consideration this and earlier isoprene studies, considerable uncertainties remain on the distribution of oxygenated products, which affect radical levels and organic aerosol downwind of unpolluted isoprene-dominated regions.

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“…Full presentations of the pressure-dependent SS-QRRK model for an irreversible unimolecular reaction are given in our previous paper 32 and in a recent review 40 for the case where the mechanism assumed is to be…”

Section: Details: Pressure Dependencementioning

confidence: 99%

“…Three prototypical OOQOOH species and the corresponding reactions of [1,5] H-shift. A and B are studied here and C are studied in the previous article 32 .…”

Section: Introductionmentioning

confidence: 99%

Relative Rates of Hydrogen Shift Isomerizations Depend Strongly on Multiple-Structure Anharmonicity

et al. 2018

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Hydroperoxyalkylperoxy species (OOQOOH) are important intermediates that are generated during the autoignition of transport fuels. A key reaction of hydroperoxyalkylperoxy radicals is a [1,5] hydrogen shift, for which kinetics data are experimentally unavailable. Here we study two typical OOQOOH reactions and compare their kinetics to one another and to a previous study to learn the effect of structural variations of the alkyl group on the competition between alternative [1,5] hydrogen shifts of hydroperoxyalkylperoxy species. We use electronic structure calculations to determine previously missing thermochemical data, and we use variational transition state theory (VTST) with multidimensional tunneling (MT), multiple structures, torsional potential anharmonicity, and high-frequency anharmonicity to obtain more accurate rate constants than the ones that can computed by conventional single-structure harmonic transition state theory (TST) and than the empirically estimated rate constants that are currently used in combustion modeling. The calculated temperature range is 298−1500 K. The roles of various factors in determining the rates are elucidated, and we find an especially strong effect of multiple structure anharmonicity due to torsions. Thus, even though there is some cancellation between the anharmonicity of the reactant and the anharmonicity of the transition state, and even though the reactants are very similar in structure, differing only by a methyl group, the effect of multiple structure anharmonicity has a large effect on the relative rates-as large as a factor of 17 at room temperature and as large as a factor of 7 at 1500 K. This has broad implications for the estimation of reaction rates in many subfields of chemistry, including combustion chemistry and atmospheric chemistry, where rates of reaction of complex molecules are usually estimated without explicit consideration of this fundamental entropic effect. In addition, the pressure-dependence of the rate constants is modeled by system-specific quantum Rice-Ramsperger-Kassel (SS-QRRK) theory for a reversible isomerization.

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Hydrogen shift isomerizations in the kinetics of the second oxidation mechanism of alkane combustion. Reactions of the hydroperoxypentylperoxy OOQOOH radical

Cited by 26 publications

References 82 publications

Collision Efficiency Parameter Influence on Pressure-Dependent Rate Constant Calculations Using the SS-QRRK Theory

Collision Efficiency Parameter Influence on Pressure-Dependent Rate Constant Calculations Using the SS-QRRK Theory

Importance of isomerization reactions for OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

Relative Rates of Hydrogen Shift Isomerizations Depend Strongly on Multiple-Structure Anharmonicity

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