Abstract: The doublet potential energy surface for the reaction of HCCO radical with molecular O₂ is worked out by the ab initio MO calculations at the G2(B3LYP/MP2/CC) level of theory. Three kinds of possible reaction mechanisms are proposed for the reaction. The first one is the four membered ring reaction mechanism to give products P1 (HCO+CO₂); the second is the three membered ring reaction mechanism to give products P2 (CO+HCO₂); the third is the O—O bond broken mechanism to give products P3[O+OCC(O)H] and products P4(O+CO+HCO). Products P1 (HCO+CO₂) are the major products on the potential energy surface,and products P2 (CO+HCO₂),P3 [O+OCC(O)H] and P4 (O+CO+HCO) are the minor ones.

Key words: Ketenyl radical, Oxygen, Potential energy surface