Theoretical study on reaction mechanism of the HCCCO radical with oxygen

The potential energy surface of complex doublet for the HCCCOOO system is investigated in this paper at the hybrid density functional B3LYP and CCSD(T) (single-point) levels with 6-311 G(d,p) basis set in order to find out the reaction mechanism of the radical HCCCO with oxygen. Nineteen minimum isomers and 22 transition states are located and a variety of possible reaction pathways are probed. In this article, we discussed five products P-1 HCCO + CO2, P-2) HCO + 2CO, P-3 HCO2 + C2O, P-4 H + 3CO and P-5 H + CO2 + C2O. The reaction pathway leading to the major HCCO + CO, product is as following: HCCCO + O-2 --> a(3) --> TSa(3)/b(3) --> b(3) --> TSb3/b(4) --> b(4) --> TSb4/p(1), in which the rate-determining step is isomer a(3) overcomes the barrier (27 kcal/mol) to form the isomer b(3). It is an interesting process for it keeps the Cs symmetry in the reaction. Another important pathway leading to HCO+2CO product is the formation of d(1) isomer. Once the structure of d(1) is formed, it will directly dissociate to g+CO. Calculation on these would be useful for our understanding about the reactions of CCCO+O-2. (C) 2004 Elsevier B.V. All rights reserved.