Mechanism and kinetics of the reaction of acetylene and nitric oxide

The potential energy surface (PES) of a [C-2,H-2,N,O] system in its electro nic doublet ground state has been investigated using density functional the ory method, at B3LYP/6-311++G(3df,2p)// B3LYP/6-311++G(d,p) level. Twelve s table intermediate radicals including trans-nitrosoethenyl 1, cis-nitrosoet henyl 2, iminoketenyl 11, and aminoketenyl 12 radicals have been located. O ther stationary points on the PES formed from hydrogen migration and dissoc iation channels of these intermediates have been identified. Barrier height s, vibrational wavenumbers and moments of inertia were then utilized in the calculations of rate constants using quantum Rice-Ramsperger-Kassel (QRRK) theory. The total rate constant is found to increase with increase of temp erature. At temperatures below 1000 K, only a rapid equilibrium is establis hed between the reactants and the trans-nitrosoethenyl 1 radical which, in turn, suggests an absence of a reaction at low temperatures. HCO + HCN is f ound to be the predominant product at high temperatures and it involves fiv e isomers of [C-2,H-2,N,O] system as intermediates with the formation of th e four-membered ring 3 as the rate determining step. The rate constant for the formation of HCO + HNC is found to be 2 orders of magnitude lower than that for HCO + HCN. The total rate constant is pressure independent at low pressures up to atmospheric pressure. The calculated total rate constant at 2000 K and 1 atm pressure is 7.9 x 10(4) cm(3) mol(-1) s(-1).