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In this study, the density functional theory (DFT) and CCSD(T) method have been performed to gain insight into the possible products and detailed reaction mechanism of the Criegee intermediate (CI) of anti-PhCHOO with SO2 for the first time. The potential energy surfaces (PESs) have been depicted at the UCCSD(T)/6-311++G(d,p)//UB3LYP/6-311++G(d,p) levels of theory with ZPE correction. Two different five-membered ring adducts, viz., endo PhCHOOS(O)O (IM1) and exo PhCHOOS(O)O (IM2) have been found in the entrance of reaction channels. Both direct and indirect reaction pathways from IM1 and IM2 have been considered for the title reaction. Our calculations show that the formation of PhCHO+SO3 (P1) via indirect reaction pathways from IM1 is predominant in all the pathways, and the production of P1 via direct dissociation pathway of IM1 and indirect reaction pathways of IM2 cannot be neglected. Moreover, PhCOOH+SO2 (P2) initiated from IM2 is identified as the minor product. According to the kinetic calculation, the total rate constant for the anti-PhCHOO+SO2 reaction is estimated to be 6.98 × 10−10 cm3·molecule−1·s−1 at 298 K.

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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.

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