Bimolecular kinetics of Criegee intermediate (CH₂OO) with 2-pentanone: experimental and theoretical analysis in...

Temperature-dependent kinetics of Criegee intermediate (CH₂OO) with 2-pentanone were performed at 258-318 K and 50 Torr using pulsed laser photolysis-cavity ring-down spectroscopy (PLP-CRDS) technique. The measured room temperature rate coefficient was (3.84 ± 0.24) × 10^-13 cm³ molecule^-1 s^-1. The reaction follows a negative temperature dependency, and the corresponding Arrhenius equation is k₄ = (1.76 ± 0.36) × 10^-15exp{(3.18 ± 0.11) kcal mol^-1/RT}. The high-P limit rate coefficients obtained using CVT/SCT at CCSD(T)/aug-cc-pVTZ//B3LYP/6-311 + G(2df,2p) level of theory deviate from the experimental results, especially in the low-temperature region. At 258 K, the computed high-P limit rate coefficient exceeded the experimental value by more than a factor of four. Comparing all the reaction pathways, HCOOH was the major product formed in the title reaction. The atmospheric lifetime of 2-pentanone due to its reaction with CH₂OO was calculated to be ~ 3000 days, rendering the reaction insignificant for inclusion in models of atmospheric 2-pentanone.