Cn, Cp, And Of Nco With Ch <sub> 2 </ Sub> Co Reaction Theory

The bimolecular single collision reaction potential energy surface of CN, NCO, CP radical with ketene (CH₂CO) were investigated by means of B3LYP and QCISD(T) methods. The calculated results indicate that there are three possible channels in the reaction. The first is an attack reaction by the carbon atom of CN at the carbon atom of the methylene of CH₂CO to form the intermediate NCCH₂CO followed by a rupture reaction of the C-C bond combined with -CO group to the products CH₂CN + CO. The second is a direct addition reaction between CN and CH₂CO to form the intermediate CH₂C(O)CN followed by its isomerization into NCCH₂CO via a CN-shift reaction, and subsequently, NCCH₂CO dissociates into CH₂CN + CO through a CO-loss reaction. The last is a direct hydrogen abstraction reaction of CH₂CO by CN radical. Because of the existence of a 15.44 kJ/mol reaction barrier and higher energy of reaction products, the path can be ruled out as an important channel in the reaction kinetics. The computed results indicate that two possible reaction channels exist on the surface. One is an addition-elimination reaction process, in which the CH₂CO molecule is attacked by the nitrogen atom at its methylene carbon atom to lead to the formation of the intermediate OCNCH₂CO followed by a C-C rapture channel to the products CH₂NCO + CO. The other is a direct hydrogen abstraction channel from CH₂CO by the NCO radical to the products HCCO + HNCO. Because of a higher barrier 36.69 kJ/mol in the hydrogen abstraction reaction than that in the addition-elimination reaction, the direct hydrogen abstraction pathway can only be considered as a secondary reaction channel in the reaction kinetics of NCO + CH₂CO. The predicted results are in good agreement with previous experimental and theoretical investigations. For the system of the CP radical with CH₂CO, the computation results demonstrated that the reaction, proceeding through a barrierless initial attack by the carbon atom of CP at theβ-carbon atom of CH₂CO leading to the formation of PCCH₂CO followed by a direct dissociation into the major products CH₂CP + CO via a C-C bond rupture reaction, can be considered as the dominant pathway in the reaction kinetics of CP with CH₂CO. By comparison with the CN + CH₂CO system, it can be known that the two reactions possess quite similar reaction mechanism and product distribution. Furthermore, the structural nature of several thermodynamically favorable intermediates was investigated. Also, the ring strain energies of two low-lying cyclic intermediates were calculated for illuminating their slightly high thermodynamic stabilities relative to another two chainlike low-lying intermediates.