Theoretical study of the reaction of CH3C(2A″, ã4A2) with N2

Abstract

The reaction of CH₃C( ²A″, ã⁴A₂) with N₂ has been studied using four ab initio methods, namely UMP2, CASSCF, QCISD and G3. Both reaction mechanism and kinetics are the subjects of this study. The CH₃CN + N(⁴S) product channel, which is of most importance, occurs on two distinct pathways. One is a direct addition–elimination process on the quartet surface: CH₃C(ã⁴A₂) + N₂ → CH₃CNN(⁴A″) → CH₃CN + N(⁴S). The net barrier heights for addition and elimination steps are 13.7–15.0 kcal mol⁻¹ and 8.7–12.6 kcal mol⁻¹, respectively. The other is a doublet–quartet hypersurface crossing mechanism starting from the CH₃C(²A″) + N₂ asymptote. Although both the initial entrance channel and the exit channel involve the low energy barriers, a significant barrier separating CH₃CNN(²A″) from CH₃C(N)N(²A″) makes this mechanism unfavorable. The other product channels, such as CH₃ + NCN and CH₃ + CNN, are also examined. The calculated ambient rate coefficient agrees well with the experimental upper limit. It is proposed that the CH₃C(ã⁴A₂) + N₂ reaction, with the production of N(⁴S) atoms, might be responsible for the formation of prompt NO in flame fronts.