Reactions of Carbonyl Oxide with Aldehydes: Accurate Electronic Structure Methods, Kinetic Insights, and Atmospheric Implications

Abstract. Carbonyl oxide (CH₂OO) is paramount in atmospheric oxidation chemistry, yet quantitative kinetics data for its bimolecular reactions are very limited and even unknown. Here we establish a computational framework to obtain quantitative kinetics from small to large reaction systems. For CH₂OO + HCHO, we develop electronic structure methods to reach CCSDTQ/CBS accuracy for its activation enthalpies at 0 K. For CH₂OO + aldehydes (RCHO; R = CH₃-C₅H₁₁, CH₂F, CHF₂, CF₃), we introduce two strategies that recover CCSDTQ/CBS-quality activation enthalpies at 0 K. A dual-level strategy has been used to calculate their kinetics. The calculated rate constants show excellent agreement with available experimental data for CH₂OO + RCHO (R = CH₃–C₃H₇), which validates the designed computational framework. We find that fluorination leads to exceptional rate enhancement, with reactions of CHF₂CHO and CF₃CHO exceeding 10^⁻10 cm³ molecule^⁻1 s^⁻1 over 200–320 K, approaching the collision limit. We also find that fluorination-driven reactivity enhancement originates predominantly from lower-level electronic effects than that of post-CCSD(T). Incorporation of the kinetics into a global chemical transport model uncovers previously unrecognized atmospheric impacts, with CH₂OO + HCHO reducing nighttime CH₂OO and gas-phase sulfate concentrations by 25.3 % in Antarctica and 12.2 % over Canada, respectively. The present findings address a long-term challenge in how to obtain quantitative kinetics for large molecular systems, where post-CCSD(T) calculations are prohibitive and provide new insights into the chemical transformation of CH₂OO and fluorinated aldehydes in the atmosphere.