Spin-forbidden F+ transfer between (NF+)-N-2 and CO: a computational studyon the detailed mechanistic aspects

The detailed mechanistic aspects of the ion-molecule reaction between (NF+) -N-2 and CO with formation of (FCO+)-F-1 and N-4 have been investigated by using density functional theory and ab initio calculations. We have first l ocated on the ground doubler and quarter B3LYP/6-311+G(d) (N,F,C,O)(+) pote ntial energy surfaces the various energy minima and transition structures i nvolved in this process, and subsequently located the minimum energy points lying on the B3LYP/6-311+G(d) line of intersection between the two surface s by using a recently described steepest descent-based method [Theor. Chem. Acc. 99 (1998) 95], The obtained results indicate that this "spin-forbidde n" reaction is a viable process in the gas phase, and could occur by two al ternative mechanisms. The first one consists of the formation of the ((NF+) -N-2/CO) adduct 1 on the doubler (N,F,C,O)(+) surface, which subsequently u ndergoes the spin-forbidden isomerization into the loosely bound adduct (N- 4/FCO+) adduct 5 on the quartet surface via a 1,2 fluorine shift from nitro gen to carbon. Isomer 5 undergoes in turn the barrier-free dissociation int o the N-4 and FCO+ reaction products. The second conceivable mechanistic ro ute consists of the formation of the adduct 1 and its isomerization into th e (N-2/FCO+) adduct 7 via an adiabatic process. The eventual spin-forbidden formation of isomer 5 from isomer 7 occurs by a nonadiabatic 1,2 fluorine shift from nitrogen to carbon. (C) 2000 Elsevier Science B.V.