The radical-radical reaction between CN ((2)Sigma) and O-2 ((3)Sigma(g)) has been theoretically investigated at the UCCSD(T)/6-311+G(d)//UB3LYP/6-31+G(d) level. This reaction proceeds most likely through the doublet CNO= potential energy surface (PES) initiated by the carbon-to-oxygen attack leading to the linear NCOO ((2)A") radical, followed by the direct oxygen-oxygen single-bond cleavage leading to (A) OCN ((2)Sigma) + O (P-3), or by the sequential three-centered isomerizations and final dissociations leading to (B) CO ((1)Sigma) + NO ((2)Pi) and (C) CO2 ((1)Sigma(g)) + N (D-2). This study may be helpful for understanding the combustion chemistry of nitrogen-containing compounds. (C) 2002 Published by Elsevier Science B.V.