Density functional (B3LYP) calculations, using the cc-pVDZ and cc-pVTZ basis sets, have been employed to study the reaction pathway involving ketyl radical (HCCO: 2A″) and oxygen molecule (O₂: ³∑_g^-).Based on B3LYP/cc-pVDZ geometries, single point CCSD(T)/cc-pVDZ energy calculations have been performed to get more accurate energies.In addition, G3B3 theory with B3LYP/6-31G^* geometries and frequencies has also been used for comparison.The obtained results show that the energy barriers are only 6.31 kJ/mol or 6.23 kJ/mol for the process of oxygen atom in O₂ attacking the terminal carbon of ketyl radical to form two open-ring intermediates, the total energies of which are 88.11 kJ/mol and 84.85 kJ/mol below the reactants, respectively.After that they could easily be converted to other two more stable annular isomers, the total energies of which are 149.81 kJ/mol and 54.97 kJ/mol below the reactants by cyclizing C—C—O—O or C—O—O with a barrier of 8.73 kJ/mol and 86.44 kJ/mol, respectively.Both of the annular isomers can easily be decomposed into the final products H+CO+CO₂.All other possible reaction channels are also reported.

Key words: ketyl radical, O₂, density function theory, radical reaction