• SN2 reaction;
  • F;
  • NH2F;
  • ab initio direct classical trajectory;
  • central barrier recrossing


The bimolecular nucleophilic substitution (SN2) reaction of Fa with NH2Fb has been investigated with the ab initio direct classical trajectory method. According to our trajectory calculations, a dynamic behavior of nonstatistical central barrier recrossing is revealed. Among the 64 trajectories calculated in this work, 45 trajectories follow the dynamic reaction pathways as assumed by statistical theory and other 19 trajectories with central barrier recrossings are nonstatistical. For the nonstatistical trajectories, the central barrier recrossings may originate from the inefficient kinetic energy transfer from the intramolecular modes of the NH2Fa moiety in the dynamic FbH[BOND]NH[BOND]Fa complex to the intermolecular modes of the dynamic FbH[BOND]NH[BOND]Fa complex on the exit-channel potential energy surface. With respect to the dynamic behavior of the nonstatistical central barrier recrossing, the statistical theories such as the Rice-Ramsperger-Kassel-Marcus and transition state theories without further corrections cannot be used to model the reaction kinetics for this SN2 reaction. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2012