A Theoretical Study on the Potential Energy Surface of the C2 + NO Reaction

The reaction of C2 radical with NO molecule is studied at the B3LYP/6-311G(d) level of theory. Both doublet and quartet potential energy surfaces (PES) are considered. On the doublet potential energy surface, we obtain four major pathways in which the pathways C2 + NO h 1 CCNO f 2 (NC)CO f 3 CNCO f P1 CN + CO and C2 + NO h 1 f 4 CC(NO) f 2 f 3 f P1 CN + CO have lower energetics than the other two pathways that form the 3O atom, namely C2 + NO h 1 CCNO f P2 3O + 2CCN and C2 + NO h 1 CCNO f 5 ON(CC) f P3 3O + CCNring. However, the latter two pathways may compete with the former two pathways. The calculated energetics of the four pathways may account for the experimental results that CN is the primary product at low temperatures and 3O is the main product at higher temperatures. The barrierless entrance to the first adduct isomer 1 and the tight transition states to the products P1, can provide a reasonable explanation for the experimentally observed negative temperature dependence of rate constants at low temperatures. The pathways on the quartet potential energy surface are less competitive than those on the doublet potential energy surface. Thus, they are negligible.