Trajectory studies of SN2 nucleophilic substitution. 7. F- + CH3Cl → FCH3 + Cl-

Timothy Su, Haobin Wang, William L. Hase

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The PES(F,Cl) analytic potential energy surface, developed previously, is used in a trajectory study of the F- + CH3Cl SN2 reaction. The trajectory SN2 rate constants, as a function of reactant relative translational energy Erel and CH3Cl 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 Erel the reaction is direct. At lower Erel 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 Erel but becomes anisotropic with forward scattering as Erel 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 CH3Cl rotational temperature, the total angular momentum is dominated by the reactant orbital angular momentum, which is strongly correlated with the product orbital angular momentum.

Original languageEnglish
Pages (from-to)9819-9828
Number of pages10
JournalJournal of Physical Chemistry A
Issue number48
StatePublished - Nov 26 1998


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