Tropospheric Oxidation of 1H-Heptafluorocyclopentene (cyc-CF2CF2CF2CF═CH−) with OH Radicals: Reaction Mechanism, Kinetics, and Global Warming Potentials

The present work represents the reaction mechanism and kinetics study of the 4-methyl-3-penten-2-one initiated by OH radicals. The geometries of all stationary points are optimized at the M06-2X/6-311+ +G(d,p) level of theory, and the energy values are refined by making single point energy calculation at the CCSD(T)/6-311++G(d,p) level of theory to construct an energy-level diagram. By employing conventional transition state theory along with a tunneling coefficient, the overall rate constants are calculated in the temperature range of 180−360 K and can be summarized by a modified Arrhenius three-parameter fit expression: k (T) = 6.72 × 10 −20 × T 2.5 × exp (2056.4/T) cm 3 molecule −1 s −1 . The rate constant obtained at 298 K is found to be 1.02 × 10 −10 cm 3 molecule −1 s −1 , which is in good agreement with the experimental data. In the atmosphere, the major oxidation products of the title reaction are acetone, methyl glyoxal, (CH 3 ) 2 COHC(O)H, CO 2 , and formaldehyde, which are in accordance with experimental detection. The atmospheric lifetime of 4-methyl-3-penten-2-one initiated by OH radicals and the impact of products on tropospheric chemistry have been provided in the paper.

Section: Resultssupporting

confidence: 90%

Theoretical Investigations of the OH-Initialized Oxidation of 4-Methyl-3-Penten-2-One in the Atmosphere

Zhang

2022

“…The rate coefficient k 2 can be modeled with conventional transition-state theory , k 2 = σ κ k normalB T h Q TS Q RC exp ( − E TS − E RC RT ) where h is the Planck constant, k B is the Boltzmann constant, R is the gas constant, T is temperature, and σ is the reaction-path symmetry number. The tunneling correction factor κ is evaluated according to the asymmetric Eckart model …”

Section: Methodsmentioning

confidence: 99%

Kinetics, Products, and Mechanisms Study of the Atmospheric Degradation of (E)-4-Methoxy-3-buten-2-one with Hydroxyl Radicals

Zhang

2023

High-level ab initio calculations have been conducted to investigate the mechanisms and kinetics of the oxidation of (E)-4-methoxy-3-buten-2-one by hydroxyl radicals (OH) in the atmosphere. Potential energy diagrams have been constructed at the CCSD(T)/6-311++G(d,p)//BH&HLYP/6-311++G(d,p) level of theory to characterize the overall reaction mechanism. Transition-state theory, in combination with Eckart tunneling, is employed to calculate the rate coefficients for the title reaction over the 180−360 K temperature range. Rate coefficients can then be fitted to a modified form of the Arrhenius equation: k = 2.00 × 10 −13 × exp(1960.4/T) cm 3 molecule −1 s −1 . The room temperature rate coefficient is calculated to be 1.41 × 10 −10 cm 3 molecule −1 s −1 , which matches well with the experimentally reported ones. The kinetic results imply that the reaction for OH radicals with (E)-4-methoxy-3-buten-2-one mainly leads to the formation of two hydroxyalkyl radicals by the initial addition of OH radicals to the >C�C< double bond. Under NO x -contaminated atmospheric environments, the hydroxyalkyl radicals can undergo further reactions to give various products such as methyl formate, methyl glyoxal, 2-hydroxy-2-methoxyacetaldehyde, peroxyacetyl nitrate (PAN), CO 2 , and a variety of peroxyalkyl nitrates and organic nitrates, which are in qualitative agreement with the experimental observations. A discussion on the atmospheric implications is also presented.

“…The constant values of a, b, c, and d are taken from the work previously given by Gogoi et al 47 Using the atmospheric lifetime (τ) estimated in this work, the correction factor f(τ) is calculated as 0.113. Hence, the corrected IRE of CF 2 =CF− CH 2 F is 0.014 Wm −2 ppb −1 .…”

Section: Radiative Efficiency and Global Warming Potentialsmentioning

confidence: 99%

Tropospheric Oxidation of 1,1,2,3-Tetrafluoropropene (CF₂=CF–CH₂F) Initiated by ·OH Radical and Aerial Degradation of Its Product Radicals

Kakati

Dowerah

Deka

et al. 2023

Self Cite

It is essential to understand the tropospheric chemistry and environmental impact of 1,1,2,3-tetrafluoropropene (CF 2 =CF−CH 2 F) before its wide-scale applications. So, in this present work, we have performed the quantum chemical calculations of the • OH radical initiated oxidation of CF 2 =CF−CH 2 F. First, all the reaction species of the title reaction are optimized at the M06-2X/6-311+G(d,p) level of theory and then the energies are refined at the CCSD(T) level with the same basis set. The relative energy and thermochemistry estimations indicate that the addition reactions of the • OH radical to the carbon atoms of the double bond of CF 2 =CF−CH 2 F are energetically and thermodynamically more dominant rather than the direct H-abstraction reactions by the • OH radical. The rate constant and branching ratio analysis also indicate the favorability of the • OH-addition reactions over the H-abstraction reactions. The estimated overall rate constant at 298.15 K for this reaction is found to be 9.27 × 10 −13 cm 3 molecule −1 s −1 computed by variational transition state theory. The atmospheric lifetime of CF 2 = CF−CH 2 F is calculated as 12.5 days with respect to • OH reaction. The radiative efficiency is calculated as 0.016 W m −2 ppb −1 , and global warming potentials of CF 2 =CF−CH 2 F for the different time horizons are significantly low. Further, photochemical ozone creation potential is estimated as 5.55. Finally, aerial degradation of the • OH-addition product radicals was studied in the presence of the NO radical using the same quantum chemical method. From this degradation study, we have observed that CF 2 (OH)COF, FCOCH 2 F, FCFO, FCOOH, and • CH 2 F are formed as end products.