A Shock Tube Study of H Atom Addition to Cyclopentene

Theoretical investigations on mechanisms and kinetics of the CH3CFClO2· with ClO· reaction in the atmosphere

The singlet and triplet potential energy surfaces of the ClO• radical reaction with the CH₃CFClO₂• radical have been investigated at the CCSD(T)/cc-pVTZ level based on the optimized geometries at the B3LYP/6–311++G(d,p) level. On the singlet potential energy surfaces (PES), the possible reaction involves association-dissociation, direct H-abstraction and Nucleophilic Substitution 2 (S_N2) mechanisms. On the triplet PES, S_N2 displacement and direct H-abstraction reaction pathways have been investigated, which are less competitive compared with the reaction pathways on the singlet PES. The rate constants have been calculated at 10^–10 to 10¹⁰ atm and 200–3,000 K by Rice–Ramsperger–Kassel–Marcus (RRKM) theory for the important product pathways. At 200–800 K, IM1 produced (CH₃CFClOOOCl) by collisonal deactivation is dominant; at high temperatures, the production P1 (CH₃CFO + ClOOCl) becomes dominate. The calculated rate constants for CH₃CFClO₂• + ClO• are good agreement with the available experimental value. The atmospheric lifetime of CH₃CFClO₂• in ClO• is around 3.27 h. TD-DFT computations imply that IM1 (CH₃CFClOOOCl), IM2 (CH₃CFClOOClO) and IM3 (CH₃CFClOClO₂) will photolyze under the sunlight.

An ab Initio/Transition State Theory Study of the Reactions of Ċ5H9 Species of Relevance to 1,3-Pentadiene, Part II: Pressure Dependent Rate Constants and Implications for Combustion Modeling

The temperature- and pressure-dependence of rate constants for several radicals and unsaturated hydrocarbons reactions (1,3-C₅H₈/1,4-C₅H₈/cyC₅H₈ + Ḣ, C₂H₄ + Ċ₃H₅-a, C₃H₆ + Ċ₂H₃) are analyzed in this paper. The abstraction reactions of these systems are also calculated and compared with available literature data. Ċ₅H₉ radicals can be produced via Ḣ atom addition reactions to the pentadiene isomers and cyclopentene, and also by H-atom abstraction reactions from 1- and 2-pentene and cyclopentane. Comprehensive Ċ₅H₉ potential energy surface (PES) analyses and high-pressure limiting rate constants for related reactions have been explored in part I of this work ( J. Phys. Chem. A 2019, 123 (22), 9019-9052). In this work, a chemical kinetic model is constructed based on the computed thermochemistry and high-pressure limiting rate constants from part I, to further understand the chemistry of different C₅H₈ molecules. The most important channels for these addition reactions are discussed in the present work based on reaction pathway analyses. The dominant reaction pathways for these five systems are combined together to generate a simplified Ċ₅H₉ PES including nine reactants, 25 transition states (TSs), and nine products. Spin-restricted single point energies are calculated for radicals and TSs on the simplified PES at the ROCCSD(T)/aug-cc-pVTZ level of theory with basis set corrections from MP2/aug-cc-pVXZ (where X = T and Q). Temperature- and pressure-dependent rate constants are calculated using RRKM theory with a Master Equation analysis, with restricted energies used for minima on the simplified Ċ₅H₉ PES and unrestricted energies for other species, over a temperature range of 300-2000 K and in the pressure range 0.01-100 atm. The rate constants calculated are in good agreement with those in the literature. The chemical kinetic model is updated with pressure-dependent rate constants and is used to simulate the species concentration profiles for Ḣ atom addition to cyclopentane and cyclopentene. Through detailed analyses and comparisons, this model can reproduce the experimental measurements of species qualitatively and quantitatively with reasonably good agreement.

Computational study on the mechanisms and kinetics of the CH2BrO2 + ClO reaction in the atmosphere

The singlet and triplet potential energy surfaces for the CH₂BrO₂ + ClO reaction are studied at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level. CH₂BrO₂ is revealed to react with ClO through two kinds of mechanisms on the triplet potential energy surface (PES), namely, S_N2 displacement and H-abstraction, and the production of P3 (CHBrO₂ + HOCl) via H-abstraction is the dominant channel. Addition/elimination and S_N2 displacement mechanisms exist on the singlet PES and are more complicated. The RRKM calculations of the mechanism and product distribution in the CH₂BrO₂ + ClO reaction show that the stabilization of IM1 (CH₂BrOOOBr) is dominant at T ≤ 600 K, while the pathway of producing P1 (CHBrO + HO₂ + Cl) occupies the entire reaction at T > 600 K. The total rate constants are independent of pressure, while the individual rate constants are sensitive to pressure. The lifetime of CH₂BrO₂ in the presence of ClO is estimated to be 20.27 h. Moreover, time-dependent density functional theory (TDDFT) calculations suggest that IM1 (CH₂BrOOOCl), IM2 (CH₂BrOOClO) and IM3 (CH₂BrOClO₂) will photolyze under the sunlight.

The singlet and triplet potential energy surfaces for the CH₂BrO₂ + ClO reaction are studied at the CCSD(T)/cc-pVTZ//B3LYP/6-311++G(d,p) level.