REACTION MECHANISM OF THE CCN RADICAL WITH NITROGEN DIOXIDE

Abstract

The complex singlet and triplet potential energy surfaces (PESs) of the [ C 2 N 2 O 2] system are performed at the B3LYP and Gaussian-3//B3LYP levels in order to investigate the possibility of the carbyne radical CCN in removal of nitrogen dioxide. Thirty minimum isomers and 36 transition states are located. Starting from the very energy-rich reactant R CCN + NO 2, the terminal C -attack adduct NCCN ( O ) O (singlet at -48.6 and triplet at -48.1 kcal/mol) is first formed on both singlet and triplet PESs. Subsequently, the singlet NCCN ( O ) O takes an O -transfer to form the intermediate singlet cis- NCC ( O ) NO (-120.1), which can lead to the fragments NCCO + NO (-94.4) without barrier. The simpler evolution of the triplet NCCN ( O ) O is the direct N – O rupture to form the final fragmentation NCCNO + 3 O (-31.0). However, the lower lying products 3 NCNO + CO (-103.3) and NCNCO + 3 O (-86.5) are kinetically much less competitive. All the involved transition states for the generation of NCCO + NO and NCCNO + 3 O lie much lower than the reactants, and it indicates that this reaction can proceed effectively even at low temperatures. We expect that the reaction CCN + NO 2 can play a role in both combustion and interstellar processes. Comparison is made between the CCN + NO 2 and CH + NO 2 reaction mechanisms.