title: A Computational Re-examination of the Criegee Intermediate-Sulfur Dioxide Reaction.
abstract: The atmospheric oxidation of sulfur dioxide by the parent and dimethyl Criegee intermediates (CIs) may be an important source of sulfuric acid aerosol, which has a large impact on radiative forcing and therefore upon climate. A number of computational studies have considered how the CH2OOS(O)O heteroozonide (HOZ) adduct formed in the CI + SO2 reaction converts SO2 to SO3. In this work we use the CBS-QB3 quantum chemical method along with equation-of-motion spin-flip CCSD(dT) and MCG3 theories to reveal new details regarding the formation and decomposition of the endo and exo conformers of the HOZ. Although ∼75% of the parent CI + SO2 reaction is initiated by formation of the exo HOZ, hyperconjugation preferentially stabilizes many of the endo intermediates and transition structures by 1-5 kcal mol(-1). Our quantum chemical calculations, in conjunction with statistical rate theory models, predict a rate coefficient for the parent CI + SO2 reaction of 3.68 × 10(-11) cm(3) molecule(-1) s(-1), in good agreement with recent experimental measurements. RRKM/master equation simulations based on our quantum chemical data predict a prompt carbonyl + SO3 yield of >95% for the reaction of both the parent and dimethyl CI with SO2. The existence of concerted cycloreversion transition structures 10-15 kcal mol(-1) higher in energy than the HOZ accounts for most of the predicted SO3 formation.
authors.affiliation: Department of Chemistry, Macalester College , Saint Paul, Minnesota 55105-1899, United States.
authors.forename: Keith T
authors.initials: KT
authors.lastname: Kuwata
authors.affiliation: Department of Chemistry, Macalester College , Saint Paul, Minnesota 55105-1899, United States.
authors.forename: Emily J
authors.initials: EJ
authors.lastname: Guinn
authors.affiliation: Department of Chemistry, Macalester College , Saint Paul, Minnesota 55105-1899, United States.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Hermes
authors.affiliation: Department of Chemistry, Macalester College , Saint Paul, Minnesota 55105-1899, United States.
authors.forename: Jenna A
authors.initials: JA
authors.lastname: Fernandez
authors.affiliation: Department of Chemistry, Macalester College , Saint Paul, Minnesota 55105-1899, United States.
authors.forename: Jon M
authors.initials: JM
authors.lastname: Mathison
authors.affiliation: Department of Chemistry, Macalester College , Saint Paul, Minnesota 55105-1899, United States.
authors.forename: Ke
authors.initials: K
authors.lastname: Huang