scholarly journals H migration in peroxy radicals under atmospheric conditions

2020 ◽  
Vol 20 (12) ◽  
pp. 7429-7458 ◽  
Author(s):  
Luc Vereecken ◽  
Barbara Nozière
Keyword(s):  
Transition State ◽  
Theoretical Data ◽  
Theoretical Work ◽  
State Theory ◽  
Rate Coefficients ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Hydrogen Atoms ◽  
Data Set ◽  
Wide Range

Abstract. A large data set of rate coefficients for H migration in peroxy radicals is presented and supplemented with literature data to derive a structure–activity relationship (SAR) for the title reaction class. The SAR supports aliphatic RO2 radicals; unsaturated bonds and β-oxo substitutions both endocyclic and exocyclic to the transition state ring; and α-oxo (aldehyde), –OH, –OOH, and –ONO2 substitutions, including migration of O-based hydrogen atoms. Also discussed are –C(=O)OH and –OR substitutions. The SAR allows predictions of rate coefficients k(T) for a temperature range of 200 to 450 K, with migrations spans ranging from 1,4 to 1,9-H shifts depending on the functionalities. The performance of the SAR reflects the uncertainty of the underlying data, reproducing the scarce experimental data on average to a factor of 2 and the wide range of theoretical data to a factor of 10 to 100, depending also on the quality of the data. The SAR evaluation discusses the performance in multi-functionalized species. For aliphatic RO2, we also present some experimental product identification that validates the expected mechanisms. The proposed SAR is a valuable tool for mechanism development and experimental design and guides future theoretical work, which should allow for rapid improvements of the SAR in the future. Relative multi-conformer transition state theory (rel-MC-TST) kinetic theory is introduced as an aid for systematic kinetic studies.

scholarly journals H-migration in peroxy radicals under atmospheric conditions

2020 ◽  
Author(s):  
Luc Vereecken ◽  
Barbara Nozière
Keyword(s):  
Theoretical Data ◽  
Large Data ◽  
Kinetic Studies ◽  
Theoretical Work ◽  
Rate Coefficients ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Hydrogen Atoms ◽  
Data Set ◽  
Wide Range

Abstract. A large data set of rate coefficients for H-migration in peroxy radicals is presented, and supplemented with literature data to derive a structure-activity relationship (SAR), for the title reaction class. The SAR supports aliphatic RO2 radicals, as well as unsaturated bonds and β-oxo substitution both endo- and exo-cyclic to the transition state ring, and α‑oxo (aldehyde), −OH, −OOH, and −ONO2 substitutions, including migration of O-based hydrogen atoms. Also discussed are −C(= O)OH and −OR substitutions. The SAR allows predictions of rate coefficients k(T) for a temperature range of 200 to 450 K, with migrations spans ranging from 1,4 to 1,9-H-shifts depending on the functionalities. The performance of the SAR reflects the uncertainty of the underlying data, reproducing the scarce experimental data on average to a factor of 2, and the wide range of theoretical data to a factor 10 to 100 depending also on the quality of the data. The SAR evaluation discusses the performance in multi-functionalized species. For aliphatic RO2, we also present some experimental product identification that validates the expected mechanisms. The proposed SAR is a valuable tool for mechanism development, experimental design, and guides future theoretical work, which should allow rapid improvements of the SAR in the following years; relative multi-conformer TST (rel-MC-TST) kinetic theory is introduced as an aid for systematic kinetic studies.

scholarly journals Effect of ammonia and water molecule on OH + CH3OH reaction under tropospheric condition

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mohamad Akbar Ali ◽  
M. Balaganesh ◽  
Faisal A. Al-Odail ◽  
K. C. Lin
Keyword(s):  
Water Molecule ◽  
Energy Surface ◽  
Rate Coefficient ◽  
Water Concentration ◽  
State Theory ◽  
Rate Coefficients ◽  
Hydrogen Atoms ◽  
Experimental And Theoretical Studies ◽  
Effective Reaction ◽  
Effective Reaction Rate

AbstractThe rate coefficients for OH + CH3OH and OH + CH3OH (+ X) (X = NH3, H2O) reactions were calculated using microcanonical, and canonical variational transition state theory (CVT) between 200 and 400 K based on potential energy surface constructed using CCSD(T)//M06-2X/6-311++G(3df,3pd). The results show that OH + CH3OH is dominated by the hydrogen atoms abstraction from CH3 position in both free and ammonia/water catalyzed ones. This result is in consistent with previous experimental and theoretical studies. The calculated rate coefficient for the OH + CH3OH (8.8 × 10−13 cm3 molecule−1 s−1), for OH + CH3OH (+ NH3) [1.9 × 10−21 cm3 molecule−1 s−1] and for OH + CH3OH (+ H2O) [8.1 × 10−16 cm3 molecule−1 s−1] at 300 K. The rate coefficient is at least 8 order magnitude [for OH + CH3OH(+ NH3) reaction] and 3 orders magnitude [OH + CH3OH (+ H2O)] are smaller than free OH + CH3OH reaction. Our calculations predict that the catalytic effect of single ammonia and water molecule on OH + CH3OH reaction has no effect under tropospheric conditions because the dominated ammonia and water-assisted reaction depends on ammonia and water concentration, respectively. As a result, the total effective reaction rate coefficients are smaller. The current study provides a comprehensive example of how basic and neutral catalysts effect the most important atmospheric prototype alcohol reactions.

scholarly journals Pressure-Dependent Kinetics of Peroxy Radicals Formed in Isobutanol Combustion

2020 ◽  
Author(s):  
Mark Goldman ◽  
Nathan Wa-Wai Yee ◽  
Jesse Kroll ◽  
William H. Green
Keyword(s):  
High Pressure ◽  
Reaction Rates ◽  
State Theory ◽  
Rate Coefficients ◽  
Quantum Calculations ◽  
Peroxy Radicals ◽  
Alkoxy Radical ◽  
Pressure Limit ◽  
Combustion Properties ◽  
Quantum Chemistry Calculations

Bio-derived isobutanol has been approved as a gasoline additive in the U.S., but our understanding of its combustion chemistry still has significant uncertainties. Detailed quantum calculations could improve model accuracy leading to better estimation of isobutanol’s combustion properties and its environmental impacts. This work examines 47 molecules and 38 reactions involved in the first oxygen addition to isobutanol’s three alkyl radicals located α, β, and γ to the hydroxide. Quantum calculations are mostly done at CCSD(T)-F12/cc-pVTZ-F12//B3LYP/CBSB7, with 1-D hindered rotor corrections obtained at B3LYP/6-31G(d). The resulting potential energy surfaces are the most comprehensive isobutanol peroxy networks published to date. Canonical transition state theory and a 1-D microcanonical master equation are used to derive high-pressure-limit and pressure-dependent rate coefficients, respectively. At all conditions studied, the recombination of α- isobutanol radical with O2 forms HO2 and isobutanal. The recombination of γ-isobutanol radical with O2 forms a stabilized hydroperoxy alkyl radical below 400 K, water and an alkoxy radical at higher temperatures, and HO2 and an alkene above 1200 K. The recombination of β-isobutanol radical with O2 results in a mixture of products between 700-1100 K, forming acetone, formaldehyde and OH at lower temperatures and forming HO2 and alkenes at higher temperatures. The barrier heights, high-pressure-limit rates, and pressure-dependent kinetics generally agree with the results from previous quantum chemistry calculations. Six reaction rates in this work deviate by over three orders of magnitude from kinetics in detailed models of isobutanol combustion, suggesting the rates calculated here can help improve modeling of isobutanol combustion and its environmental fate.

Sign in / Sign up

Export Citation Format

Share Document