Diatomic radical-molecule reactions HCCN ( 3A′′)+ O 2 ( $^{\sf 3}{\sf \sum}_{\sf g}^{\sf -}$ ): mechanistic study

Abstract

The possible reaction of cyanomethylene HCCN (3A′′) radical with molecular oxygen O\(_{2 }(^{3}\sum_{g}^{-})\) was studied theoretically using ab initio quantum chemistry methods and transition state theory. The potential energy surfaces were calculated at the CCSD(T)/aug-cc-pVTZ//CCSD/6-311G(d,p), and CCSD(T)/aug-cc-pVTZ//B3LYP/6-311G(d,p) levels. Various possible paths were considered. Among them, the products P1 HCN + CO2, P2 HNCO + CO, and P3 HNC + CO2 should attract our attention. In the most feasible pathways to generate these products, the relative energies of transition states are declined gradually more like a stairway. Since all of the complex, isomers, transition states, and products lie below the reactants, the rate of this pathway should be very fast even in low-temperature ranges. Furthermore, on the basis of the analysis about the kinetics of all channels in the title reaction we can interpret the remarkable difference of the title reaction with the same system reaction HCCO + NO, i.e. why HNC is the main product in the HCCN + O2 reaction while it can not be observed in the HCCO + NO reaction. The present study may be helpful for probing the mechanisms of the title reaction.