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 P₁ (CO₂ + CNO) is the major product with absolute yield, while the product P₄ (2CO + NO) is the minor product with less abundance. The other products may be undetectable. The product P₁ (CO₂ + CNO) can be obtained through R →a → b → P₁ (CO ₂ + CNO), whereas the product P₄ (2CO + NO) can be obtained through two channels R → a → b → c→ (d, g) → P₂ (OCNO + CO) → P4 (2CO + NO) and R → a →b → f →P₃ (c-OCC- O + NO) → P₄ (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.