Kinetics of gas-phase reactions of CH3 OCH2 CF3 , CH3 OCH3 , CH3 OCH2 CH3 , CH3 CH2 OCH2 CH3 , and CHF2 CF2 OCH2 CF3 with NO3 radicals at 298 K

Theoretical investigations on mechanisms and kinetics of CH2XO2 (X=F, Cl) with Cl reaction in the atmosphere

The reactions of the CH₂XO₂ (X=F, Cl) with chlorine radical have been firstly investigated utilizing the BMC-CCSD//B3LYP method. The comprehensive calculations indicate that the association-elimination and S_N2 displacement reaction mechanisms existed on the singlet potential energy surface (PES), and H-abstraction and S_N2 displacement reaction mechanism existed on the triplet PES for the CH₂XO₂ (X=F, Cl) + Cl reactions. On the triplet PES, the dominant reactions are production of P3_X (CHXO₂ (X=F, Cl) + HCl) by direct H-abstraction. On the singlet PES, three energy-rich adducts, IM1_X (CH₂XOOCl (X=F, Cl)), IM2_X (CH₂XOClO (X=F, Cl)), and IM3_X (CH₂(OX)OCl (X=F, Cl)), are produced. RRKM-computed reveals that IM1_X (CH₂XOOCl (X=F, Cl)) produced by collisional stabilization occupied the reaction T ≤ 500 and 400 K, respectively, while P1_X (CHXO (X=F, Cl) + HOCl) are forecasted to be the dominant products at high temperatures. The atmospheric lifetime of CH₂FO₂ and CH₂ClO₂ in Cl is around 1.18 and 2.50 weeks, respectively. Time-dependent density functional theory (TDDFT) computations imply that IM1_X (CH₂XOOCl (X=F, Cl)) will photolyze under the sunlight. The current results could guide us to well understand the mechanism of the CH₂XO₂ (X=F, Cl) + Cl reactions and may be helpful to understand Cl-combustion chemistry. Graphical Abstract Predicted rate constant of the dominant pathways and the total rate constants at 760 Torr, N2 in the temperature region of 200-3000 K for the CH₂XO₂ (X=F, Cl) + Cl reactions.

Quantum calculation on night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) initiated by NO3 radical

A dual-level quantum chemical calculations have been carried out on the initiation of night-time degradation of 2-chloroethyl ethyl ether (CH3CH2OCH2CH2Cl) via H-abstraction by NO3 radical. Within the scope of density functional theory, the electronic structure of all the species involved in the titled reaction has been optimized at M06-2X functional along with 6-31[Formula: see text]G(d,p) basis set. A higher level of couple cluster CCSD(T) method in conjunction with 6-311[Formula: see text]G(d,p) basis set has been used for the refined energy of the species. All minima and saddle states involved in the reaction channel have been characterized on the potential energy surface (PES). From PES, it is confirmed that H-abstraction from methylene (–CH2–) of ethyl (CH3CH2–) part of CH3CH2OCH2CH2Cl follows the minimum energy path. The rate constants (individual and overall) of the titled reaction are obtained using Canonical Transition State Theory (CTST) over the temperature range of 250–350[Formula: see text]K. The atmospheric lifetime and radiative efficiency of the titled molecule have also been estimated, amounting to 0.23 years and 0.024 years, respectively. The Global Warming Potentials of the 2-chloroethyl ethyl ether in 20 years, 100 years and 500 years time horizon were found to be 0.13, 0.04 and 0.01, respectively.

Computational exploration of regioselectivity and atmospheric lifetime in NO3-initiated reactions of CH3OCH3 and CH3OCH2CH3

The NO₃-initiated reactions of CH₃OCH₃ and CH₃OCH₂CH₃ have been investigated by the BHandHLYP method in conjunction with the 6-311G(d,p) basis set. Thermodynamic and kinetic data are further refined using the comparatively accurate CCSD(T) method. According to the values of reaction enthalpies (ΔH_r,298^θ) and reaction Gibbs free energies (ΔG_r,298^θ) from CH₃OCH₂CH₃ with NO₃ system, we find that H-abstraction pathway from the α-CH₂ group is more exothermic. It is further confirmed by the calculated CH bond dissociation energy of CH₃OCH₂CH₃ molecule. All the rate constants, computed through means of canonical variational transition state with small-curvature tunneling correction, are fitted to the three-parameter expressions k₁=1.54×10^-23T^3.34exp(-1035.53/T) and k₂=3.55×10^-26T^4.31exp(-281.24/T)cm³molecule^-1s^-1 and branching ratios are computed over the temperature range 200-600K. The branching ratios are also discussed. The atmospheric lifetimes of CH₃OCH₃ and CH₃OCH₂CH₃ determined by the NO₃ radical are about 270 and 29days, respectively.

Computational study of H-abstraction reactions from CH3OCH2CH2Cl/CH3CH2OCH2CH2Cl by Cl atom and OH radical and fate of alkoxy radicals

Multichannel gas-phase reactions of CH₃OCH₂CH₂Cl/CH₃CH₂OCH₂CH₂Cl with chlorine atom and hydroxyl radical have been investigated using ab initio method and canonical variational transition-state dynamic computations with the small-curvature tunneling correction. Further energetic information is refined by the coupled-cluster calculations with single and double excitations (CCSD)(T) method. Both hydrogen abstraction and displacement processes are carried out at the same level. Our results reveal that H-abstraction from the -OCH₂- group is the dominant channel for CH₃OCH₂CH₂Cl by OH radical or Cl atom, and from α-CH₂ of the group CH₃CH₂- is predominate for the reaction CH₃CH₂OCH₂CH₂Cl with Cl/OH. The contribution of displacement processes may be unimportant due to the high barriers. The values of the calculated rate constants reproduce remarkably well the available experiment data. Standard enthalpies of formation for reactants and product radicals are calculated by isodesmic reactions. The Arrhenius expressions are given within 220-1200 K. The atmospheric lifetime, ozone depleting potential (ODP), ozone formation potential (OFP), and global warming potential (GWP) of CH₃OCH₂CH₂Cl/CH₃CH₂OCH₂CH₂Cl are investigated. Meanwhile, the atmospheric fate of the alkoxy radicals are also researched using the same level of theory. To shed light on the atmospheric degradation, a mechanistic study is obtained, which indicates that reaction with O₂ is the dominant path for the decomposition of CH₃OCH(O•)CH₂Cl, the C-C bond scission reaction is the primary reaction path in the consumption of CH₃CH(O•)OCH₂CH₂Cl in the atmosphere.

HIGHLIGHTS

Ab initio method and canonical variational transition-state theory are employed to study the kinetic nature of hydrogen abstraction reactions of CH₃OCH₂CH₂Cl/CH₃CH₂OCH₂CH₂Cl with Cl atom and OH radical and fate of alkoxy radicals (CH₃OCH(O•)CH₂Cl/CH₃CH(O•)OCH₂CH₂Cl).

Atmospheric oxidation mechanism of OH-initiated reactions of diethyl ether – the fate of the 1-ethoxy ethoxy radical

The 1-ethoxy ethoxy radical resulting from the secondary peroxy chemistry in the oxidation of diethyl ether (DEE) by hydroxyl radical leads to the formation of ethyl formate in major quantities and ethyl acetate in minor quantities.