A Theoretical Study of Bimolecular Reaction Between SCI and Organic Acid in the Atmosphere

Criegee Intermediate is a pivotal product of the alkene ozonation reaction, which exhibits highly active chemistry. The substance under scrutiny can be decomposed by unimolecular isomerization to generate an OH radical, or alternatively undergo a bimolecular reaction with most species in the atmosphere. It is imperative to note that organic acids, which play a pivotal role in preserving acid-base equilibrium within the atmosphere, are capable of undergoing a reaction with SCI in the absence of any hindering barriers. In certain environments, the bimolecular reaction of SCI with organic acid can be observed to compete with the reaction of SCI with H2O. In this paper, the bimolecular reaction of SCI with organic acid is investigated at CCSD(T)/CBS//M06-2X/def2-TZVP level. The study obtained precise energies at near-complete basis sets and accurate reaction paths using IRC calculations. The process of reactions is characterized by significant exothermicity, and the products of hydroperoxides are notable for their stability, low decomposition rate, and minimal energy requirement. These properties suggest a potential for these compounds to serve as a substantial source of atmospheric SOA. The calculation of reaction rate coefficients was conducted using transition state theory. The rate coefficients of CH2OO with formic acid, syn-CH3CHOO with formic acid, anti-CH3CHOO with formic acid, (CH3)2COO with formic acid, CH2OO with acetic acid, and CH2OO with oxalic acid were 1.87 × 10-10, 1.59 × 10-10, 5.30 × 10-10, 1.26 × 10-10, 2.09 × 10-10 and 7.16 × 10-10 cm3 s-1, respectively. All reactions were found to be rapid in nature. Of the six reactions studied in this paper, CH2OO reacting with oxalic acid was found to be the fastest.