Statistical Rate Theory in Combustion: An Operational Approach

Olzmann, Matthias

doi:10.1007/978-1-4471-5307-8_21

Cited by 8 publications

(6 citation statements)

References 74 publications

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“…The lowest eigenvalue was determined by standard routines for tridiagonal matrices . More details and general aspects of our master equation code are given in refs and .…”

Section: Computational Sectionmentioning

confidence: 99%

Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling

et al. 2015

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“…The lowest eigenvalue was determined by standard routines for tridiagonal matrices . More details and general aspects of our master equation code are given in refs and .…”

Section: Computational Sectionmentioning

confidence: 99%

Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling

et al. 2015

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“…As expected, at higher temperatures fall-off effects become more pronounced. Especially the energetically high-lying W1-BrCH 2 + HCO channel reveals a strong pressure dependence with a pressure exponent well above 1 at low pressures, clearly a result of a pronounced weak collision effect. , With k total (772 K, 1 atm) = 1.2 × 10 –5 s –1 (corresponding to a lifetime of 1 day) and k total (1370 K, 1 atm) = 1.0 × 10 3 s –1 (corresponding to a lifetime of 1 ms), the thermal decomposition of bromoacetaldehyde is not important in the troposphere but it is fast under combustion conditions. With increasing temperature and pressure, next to the simple C–Br fission, also the HCO and HBr forming channels fCC(W1) and eHBr(W3) gain importance.…”

Section: Results and Discussionmentioning

confidence: 99%

Ab Initio and RRKM/Master Equation Analysis of the Photolysis and Thermal Unimolecular Decomposition of Bromoacetaldehyde

Sadiek

Friedrichs²,

Sakai

2021

J. Phys. Chem. A

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Bromoacetaldehyde (BrCH 2 CHO) is a major stable brominated organic intermediate of the bromine−ethylene addition reaction during the arctic bromine explosion events. Similar to acetaldehyde, which has been recently identified as a source of organic acids in the troposphere, it may be subjected to photo-tautomerization initially forming brominated vinyl compounds. In this study, we investigate the unimolecular reactions of BrCH 2 CHO under both photolytic and thermal conditions using high-level quantum chemical calculations and Rice−Ramsperger−Kassel−Marcus (RRKM)/master equation analysis. The unimolecular decomposition of BrCH 2 CHO takes place through 14 dissociation and isomerization channels along a potential energy surface involving eight wells. Under the assumption of singlet ground-state potential energy surfacedominated photodynamics, the primary photodissociation yields of BrCH 2 CHO are investigated under both collision-free and collision energy transfer conditions. At atmospheric pressure and under tropospheric actinic flux conditions at ground level, depending on the assumed collisional energy transfer parameter, 150 cm −1 < ⟨ΔE down ⟩ < 450 cm −1 , 78−33% of BrCH 2 CHO undergoes direct photodissociation instead of collisional deactivation at an excitation wavelength of 320 nm. This is significantly higher than the 14% reported for acetaldehyde, hence indicating a strong effect of bromine substitution on the product photolysis yield that is related to additional favorable Br and HBr forming dissociation channels. In contrast to the overall photodissociation quantum yield, the relative branching fractions of the photodissociation products are less dependent on the collisional energy transfer parameter. For a representative value of ⟨ΔE down ⟩ = 300 cm −1 and an excitation wavelength of 320 nm, with 27% for C−C bond fission, 11% for C−Br bond fission, 7% for HBr elimination, and only below 2% each for a consecutive O−Br fission reaction and the photo-tautomerization channel yielding brominated vinyl alcohol, the photodissociation is markedly different from the acetaldehyde case. Finally, as brominated halogenated compounds are of interest for flame inhibition purposes, thermal multichannel unimolecular rate constants were calculated for temperatures in the range from 500 to 2000 K. At a temperature of 2000 K and ambient pressure, the two main reaction channels are the C−Br and C−C bond fissions, contributing 35 and 43% to the total reaction flux, respectively.

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“…As previously mentioned, π complex dissociation occurs via a loose outer TS, so that appropriate kinetic theories have to be used for this step. In this study, we used the simplified statistical adiabatic channel model (s-SACM) − to estimate k diss . Even in the case of the ring addition reactions, where the inner TS is submerged below the reactant reference energy, the π complex dissociation was estimated to be ∼300 times faster than the forward reaction toward the OH ring adduct (on the basis of high-pressure rate coefficients, see also discussion below).…”

Section: Methodsmentioning

confidence: 99%

Reaction of OH with Aliphatic and Aromatic Isocyanates

Welz

Pfeifle

Plehiers³

et al. 2022

J. Phys. Chem. A

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Isocyanates are highly relevant industrial intermediates for polyurethane production. In this work, we used quantum chemistry and transition state theory (TST) to investigate the gas-phase reaction of isocyanates with the OH radical, which is likely one of the most significant chemical sinks for these compounds in the troposphere. para-Tolyl-isocyanate (p-tolyl-NCO) was chosen as a proxy substance for the large-volume aromatic diisocyanate species toluene diisocyanate and methylene diphenyl diisocyanate. Besides p-tolyl-NCO + OH, the model reactions CH3NCO + OH, H2CCHNCO + OH, C6H5-NCO + OH, C6H5-CH3 + OH, and C6H6 + OH have been studied as well to analyze various substituent effects and to allow for comparison with literature. Quantum chemical computations at the CCSD(T)/cc-pV(T,Q → ∞)Z//M06-2X/def2-TZVP level were used as the basis for tunneling-corrected canonical TST calculations. For CH3NCO + OH, H abstraction by OH at the methyl group is the main reaction channel according to our calculations and predicted to be four orders of magnitude faster than OH addition at the NCO group. The calculated rate coefficient (8.8 × 10–14 cm3 molecule–1 s–1) at 298 K is in good agreement with experimental data from the literature. Likewise, for aromatic isocyanates, OH attack at the isocyanate group was found to be only a minor pathway compared to addition to the aromatic ring. In the OH + p-tolyl-NCO reaction, OH addition at the ortho-position relative to the NCO group has been identified as the main initial reaction channel (branching fraction: 53.2%), with smaller but significant branching fractions for the H abstraction at the methyl group (9.6%) as well as the other ring addition reactions (ipso: 2.3%, meta: 24.5%, para: 10.5%, all relative to the NCO group). By comparing OH addition to the aromatic ring in p-tolyl-NCO with the respective ring addition reactions of phenyl isocyanate and toluene, the site-selective reactivity trends observed for ring addition in the OH + p-tolyl-NCO could be rationalized by a dominating positive mesomeric effect of the NCO group and a positive electron-donating (inductive) effect of the CH3 group. Except for the OH ring adduct formed from OH addition in ipso-position to the NCO group, we estimate the first-generation radical intermediates in the OH + p-tolyl-NCO reaction to have sufficiently long lifetimes to react with O2 under atmospheric conditions and undergo typical oxidative reaction cascades like those known for benzene or toluene.

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Statistical Rate Theory in Combustion: An Operational Approach

Cited by 8 publications

References 74 publications

Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling

Thermal Decomposition of NCN: Shock-Tube Study, Quantum Chemical Calculations, and Master-Equation Modeling

Ab Initio and RRKM/Master Equation Analysis of the Photolysis and Thermal Unimolecular Decomposition of Bromoacetaldehyde

Reaction of OH with Aliphatic and Aromatic Isocyanates

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