Trajectory Studies of SN2 Nucleophilic Substitution. 7. F- + CH3Cl → FCH3 + Cl-

The PES(F,Cl) analytic potential energy surface, developed previously, is used in a trajectory study of the F - + CH 3 Cl S N 2 reaction. The trajectory S N 2 rate constants, as a function of reactant relative translational energy E rel and CH 3 Cl temperature, are in good overall agreement with the experimental rate constants and those calculated using an ion−molecule capture/RRKM statistical model applied to PES(F,Cl). The latter agreement exists even though the reaction dynamics is decidedly nonstatistical. For high E rel the reaction is direct. At lower E rel there is evidence for formation of an ion−molecule complex; however, its lifetime is too short for complete energy randomization to occur. The velocity scattering angle is isotropic at low E rel but becomes anisotropic with forward scattering as E rel is increased. The reaction exothermicity is primarily partitioned to product vibration, in disagreement with a previous experimental study. Energy transfer from the reactants to products is very selective. Excess reactant relative translational energy almost exclusively goes to product relative translation. Similarly, C−Cl stretch excitation goes to product vibration. For a 300 K CH 3 Cl rotational temperature, the total angular momentum is dominated by the reactant orbital angular momentum, which is strongly correlated with the product orbital angular momentum.