Translational energy dependence and potential energy surfaces of gas phase SN2 and addition-elimination reactions

The translational energy dependence of several gas-phase S(N)2 and carbonyl addition-elimination reaction rate constants has been measured in an FT-ICR. The relative energy dependences of the reactions are qualitatively consistent with variations in the reaction potential surfaces that are inferred from their thermal rate constants, which comprise a wide range of reaction efficiencies. Furthermore, the observed energy dependence of each reaction agrees quantitatively with RRKM calculations of the reaction rate constants. We conclude that, although nonstatistical dynamics are observed in some SN2 reactions, statistical reaction rate theory is, in general, an accurate means of interpreting the translational energy dependence of bimolecular ion-molecule reaction rate constants.