An ab initio molecular dynamics study of the SN2 reaction F-+CH3Cl→CH3F+Cl-

The F-+CH3Cl-->CH3F+Cl- reaction has been investigated by ab initio molecular dynamics with the Car-Parrinello method. The Hamprecht, Cohen, Tozer, and Handy exchange-correlation functional produces a stable prereactive complex. Thermal effects at 300 K have been calculated in the Blue Moon ensemble. An appreciable increase in the energy barrier has been obtained at 300 K relative to the 0 K. The averaged potential energy surface at 300 K shows the presence of a stable hydrogen bonded complex. Noncollinear impact trajectories have been examined. The transition state lifetime has been estimated. The energy redistribution among the degrees of freedom following the impact shows that a large part of the energy is localized in the C-F stretch and also in the umbrella bending. (C) 2003 American Institute of Physics.