Theoretical study on reaction mechanism of the ketenylidene radical with nitrogen dioxide

The complex doublet potential-energy surface for the reaction of CCO with NO2, including 8 minimum isomers and 17 transition states, is explored theoretically using the coupled cluster and density functional theory. The association of CCO with NO2 was found to be a barrierless process forming an energy-rich adduct a (OCCNO2) followed by oxygen shift to give b (O2CCNO). Our results show that the product P-1 (CO2 + CNO) is the major product with absolute yield, while the product P-4 (2CO + NO) is the minor product with less abundance. The other products may be undetectable. The product P-1 (CO2 + CNO) can be obtained through R -> a b b -> P-1 (CO2 + CNO), whereas the product P-4 (2CO + NO) can be obtained through two channels R -> a -> b -> c ->(d, 9)-> P-2 (OCNO + CO) -> P-4(2CO + NO) and R -> a -> b -> f -> P-3 (c-OCC-O + NO) -> P-4 (2CO + NO). Because the intermediates and transition states involved in the above three channels are all lower than the reactants in energy, the CCO + NO2 reaction is expected to be rapid, which is consistent with the experimental measurement in quality. The present study may be helpful for further experimental investigation of the title reaction.