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.