Singlet (1∆g) O2 initiated gas phase oxidation as a potential tropospheric decay channel for ketene

Abstract

The oxidation of CH2CO by (1Δg) O2 has been investigated by means of high level quantum chemical and chemical kinetic calculations. The reaction was found to proceed through a four membered cyclic transition state resulting from the addition of O2 to the C=C bond of ketene. The reaction energetics has been calculated employing post-CCSD(T) corrections. The energy of the transition state was found to be 33.6 kcal mol−1 below that of the isolated reactants. The rate coefficient, calculated using master equation under tropospheric conditions, was found to be 5.1 × 10−15 cm3 molecule−1s−1 at 298 K and 1 bar. Atmospheric implications of the title reaction has been estimated by comparing the atmospheric lifetime of ketene for the title reaction against reactions with •OH, H2O and NH3. On a global scale, lifetime for the title reaction was found to be almost 70 times to that for the reaction with •OH. However, under special conditions, where the local concentration of singlet O2 is significantly higher and/or the same of •OH is significantly lower, 1O2 initiated oxidation could become the most significant tropospheric loss mechanism of CH2CO.