Singlet (1Δg) O2 as an efficient tropospheric oxidizing agent: the gas phase reaction with the simplest Criegee intermediate

Abstract

The reaction between CH₂OO and ¹Δ_g O₂ has been investigated by means of high level quantum chemical and chemical kinetic calculations. Post-CCSD(T) corrections in terms of full triplets and partial quadratic excitations, along with core corrections have been employed to estimate the reaction energetics. The title reaction was found to be effectively barrierless with the transition state lying −22.85 kcal mol⁻¹ below the isolated reactants. Rate coefficients under tropospheric conditions have been calculated using the master equation. The calculated rate coefficient was found to be marginally over the gas kinetic limit, implying that the reaction rate would be limited by the upper limit of bimolecular collision frequency. When compared against ˙OH and O₃, ¹O₂ was found to compete efficiently with the two well known tropospheric oxidants.