Reaction mechanism of the CCN radical with nitric oxide

To investigate the possibility of the carbyne radical CCN in removal of nitric oxide, a detailed computational study is performed at the Gaussian‐3//B3LYP/6‐31G(d) level on the CCN + NO reaction by constructing the singlet and triplet electronic state [C 2 N 2 O] potential energy surfaces (PESs). The barrierless formation of the chain‐like isomers NCCNO (singlet at −106.5, triplet cis at −48.2 and triplet trans at −47.6 kcal/mol) is the most favorable entrance attack on both singlet and triplet PESs. Subsequently, the singlet NCCNO takes an O‐transfer to form the branched intermediate singlet NCC(O)N (−85.6), which can lead to the fragments CN + NCO (−51.2) via the intermediate singlet NCOCN (−120.3). The simpler evolution of the triplet NCCNO is the direct N–O rupture to form the weakly bound complex triplet NCCN…O (−56.2) before the final fragmentation to NCCN + 3 O (−53.5). However, the lower lying products 3 NCN + CO (−105.6) and 3 CNN + CO (−74.6) are kinetically much less competitive. All the involved transition states for generation of CN + NCO and NCCN + 3 O lie much lower than the reactants. Thus, the novel reaction CCN + NO can proceed effectively even at low temperatures and is expected to play a role in both combustion and interstellar processes. Significant differences are found on the singlet PES between the CCN + NO and CH + NO reaction mechanisms. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 883–893, 2006