Theoretical study of the reaction of CH3C((X)over-tilde (2)A '', (a)over-tilde (4)A(2)) with N-2

The reaction of CH3C((X) over tilde (2)A ", (a) over tilde (4)A(2)) with N- 2 has been studied using four ab initio methods, namely UMP2, CASSCF, QCISD and G3. Both reaction mechanism and kinetics are the subjects of this stud y. The CH3CN + N(S-4) product channel, which is of most importance, occurs on two distinct pathways. One is a direct addition-elimination process on t he quartet surface: CH3C((a) over tilde (4)A(2)) + N-2 --> CH3CNN((4)A ") - -> CH3CN + N(S-4). The net barrier heights for addition and elimination ste ps 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 th e CH3C((X) over tilde (2)A ") + N-2 asymptote. Although both the initial en trance channel and the exit channel involve the low energy barriers, a sign ificant barrier separating CH3CNN((2)A ") from CH3C(N)N((2)A ") makes this mechanism unfavorable. The other product channels, such as CH3 + NCN and CH 3 + CNN, are also examined. The calculated ambient rate coefficient agrees well with the experimental upper limit. It is proposed that the CH3C((a) ov er tilde (4)A(2)) + N-2 reaction, with the production of N(S-4) atoms, migh t be responsible for the formation of prompt NO in flame fronts.