Using the density function theory(DFT)and ab initio calculation, the reaction of ethynyl radical with oxygen was studied. At 6-311G (d,p) level with DFT method, the geometries of all species (reactants, transition states and products) were optimized and the vibration frequencies and zero point vibration energies (ZPVE) were also calculated. All the energies of the species were obtained with the correction of ZPVE at the same base set level with CCSD method. The calculated results suggest that the ethynyl radical attacks the site of O-atom of oxygen to form the I₁, isomer 1 (HCCOO). The I₁ undergoes different channels and can form five products, i.e. P₁ (HCO+CO), P₂ (HCCO+O), P₃ (CO₂+CH), P₄ (C₂O+OH) and P₅ (2CO+H). A notable finding is that the P₁ and P₂ are the main products, and the P₅ is much less competitive, while the P₃ and P₄ are unfeasible due to the potential energy surface (PES). This investigation could excellently explain the experiment of the title reaction.

Key words: ab initio calculation, density functional theory, reaction channel, ethynyl radical