Computational investigation into the gas-phase ozonolysis of the conjugated monoterpene α-phellandrene

Compilation of reaction kinetics parameters determined in the Key Development Project for Air Pollution Formation Mechanism and Control Technologies in China

A compilation of new advances made in the research field of laboratory reaction kinetics in China's Key Development Project for Air Pollution Formation Mechanism and Control Technologies was presented. These advances are grouped into six broad, interrelated categories, including volatile organic compound (VOC) oxidation, secondary organic aerosol (SOA) formation, new particle formation (NPF) and gas-particle partitioning, ozone chemistry, model parameters, and secondary inorganic aerosol (SIA) formation, highlighting the laboratory work done by Chinese researchers. For smog chamber applications, the current knowledge gained from laboratory studies is reviewed, with emphasis on summarizing the oxidation mechanisms of long-chain alkanes, aromatics, alkenes, aldehydes/ketones in the atmosphere, SOA formation from anthropogenic emission sources, and oxidation of aromatics, isoprene, and limonene, as well as SIA formation. For flow tube applications, atmospheric oxidation mechanisms of toluene and methacrolein, SOA formation from limonene oxidation by ozone, gas-particle partitioning of peroxides, and sulfuric acid-water (H₂SO₄-H₂O) binary nucleation, methanesulfonic acid-water (MSA-H₂O) binary nucleation, and sulfuric acid-ammonia-water (H₂SO₄-NH₃-H₂O) ternary nucleation are discussed.

Kinetics and Thermodynamics of Reactions Involving Criegee Intermediates: An Assessment of Density Functional Theory and Ab Initio Methods Through Comparison with CCSDT(Q)/CBS Data

Reactions involving Criegee intermediates (CIs, R₁ R₂ COO) are important in atmospheric ozonolysis models. In recent years, density functional theory (DFT) and CCSD(T)-based ab initio methods are increasingly being used for modeling reaction profiles involving CIs. We obtain highly accurate CCSDT(Q)/CBS reaction energies and barrier heights for ring-closing reactions involving atmospherically important CIs (R₁ /R₂ = H, Me, OH, OMe, F, CN, cyclopropene, ethylene, acetaldehyde, and acrolein). We use this benchmark data to evaluate the performance of DFT, double-hybrid DFT (DHDFT), and ab initio methods for the kinetics and thermodynamics of these reactions. We find that reaction energies are more challenging for approximate theoretical procedures than barrier heights. Overall, taking both reaction energies and barrier heights into account, only one of the 58 considered DFT methods (the meta-GGA MN12-L) attains near chemical accuracy, with root-mean-square deviations (RMSDs) of 3.5 (barrier heights) and 4.7 (reaction energies) kJ mol^-1 . Therefore, MN12-L is recommended for investigations where CCSD(T)-based methods are not computationally feasible. For reaction barrier heights performance does not strictly follow Jacob's Ladder, for example, DHDFT methods do not perform better than conventional DFT methods. Of the ab initio methods, the cost-effective CCSD(T)/CBS(MP2) approach gives the best performance for both reaction energies and barrier heights, with RMSDs of 1.7 and 1.4 kJ mol^-1 , respectively. All the considered Gaussian-n methods show good performance with RMSDs below the threshold of chemical accuracy for both reaction energies and barrier heights, where G4(MP2) shows the best overall performance with RMSDs of 2.9 and 1.5 kJ mol^-1 , respectively. © 2019 Wiley Periodicals, Inc.

Ozonolysis of 3-carene in the atmosphere. Formation mechanism of hydroxyl radical and secondary ozonides

The gas-phase ozonolysis mechanism of 3-carene is investigated using high level quantum chemistry and kinetic calculations. The reaction follows the Criegee mechanism with an initial addition of O₃ to the [double bond splayed left]C[double bond, length as m-dash]C[double bond splayed right] bond, followed by a chain of unimolecular isomerizations, as 3-carene + O₃→ POZs (primary ozonides) → CIs (Criegee intermediates, 4 conformers) → Ps (products). In the course of the reaction, a large excess of energy retained in the POZs* lead to the prompt unimolecular processes in POZs*, CIs*, and Ps*, and only ∼4% of CIs* could be stabilized by collision at 298 K and 760 Torr. From RRKM-ME calculations, the VHPs* could further dissociate to vinoxy-type radical and OH radical, the SOZs* could isomerize to 3-caronic acid, and DIOs* could be stabilized via collision. The fractional yield of OH radical, in the range of 0.56 to 0.59, agrees reasonably well with the previously measured value of 1.06 (with an uncertainty factor of 1.5).

Detailed kinetics of tetrafluoroethene ozonolysis

The C2F4 + O3 reaction plays an important role in the oxidation process of perfluoroalkenes in the atmosphere. The detailed reaction mechanism was explored using the accurate electronic structure method, CCSD(T)/CBS//B3LYP/aug-cc-pVTZ. The 1,3-cycloaddition of O3 with C2F4 to form the primary ozonide was found to be the rate-determining step of the oxidation process with a small barrier (i.e., 7.3 kcal mol-1 at 0 K). The temperature- and pressure-dependent behaviors of the title reaction were characterized in the range of 200-1000 K & 0.1-760 Torr using the integrated deterministic and stochastic master equation/Rice-Ramsperger-Kassel-Marcus (ME/RRKM) rate model with the inclusion of the corrections for anharmonicity and tunneling treatments. It is found that the anharmonic effect plays a role in the kinetic behaviors (e.g., lower the rate by a factor of ∼ two at 298 K) while the tunneling correction is insignificant. The total rate constants were found to be pressure-independent under the considered conditions, shown as ktot(T) = 4.80 × 10-23 × T2.69 × exp(-2983.4 K/T) (cm3 per molecule per s), which confirms the latest experimental data by Acerboni et al. (G. Acerboni, N. R. Jensen, B. Rindone and J. Hjorth, Chem. Phys. Lett., 1999, 309, 364-368); thus this study helps to resolve a long-term controversy among the previous measurements. The sensitivity analyses on the derived rate coefficients and time-resolved species mole fraction with respect to the ab initio input parameters were also performed to further understand as well as quantify the kinetic behaviors for the title reaction.

Hyperconjugation enhances electrophilic addition to monocyclic monoterpenes: a Fukui function perspective

The local and condensed Fukui functions as well as the principle of hard and soft acids and bases were used to study the addition of free radicals to the exocyclic and endocyclic double bonds of seven monocyclic monoterpenes of formula C₁₀H₁₆. The results obtained showed that, in general, the most reactive double bond was the one with the most substituents on the double-bonded carbon atoms, and that the reaction of a double bond with an electrophile is a soft-soft interaction. The effects of substituents on the double-bonded carbon atoms and the stabilization of the monoterpenes were interpreted by invoking hyperconjugated structures, which led us to propose a simple rule: the larger the value of the Fukui function for the double bond, the greater the hyperconjugative stabilization and the susceptibility of the double bond to electrophilic attack. In general, our results are in good accordance with relevant experimental and theoretical results published in the literature. Graphical abstract The specific electrophilic addition to monocyclic monoterpenes.