Classical trajectory studies of the reaction F + CH3I → IF + CH3

Abstract

The reaction F + CH₃I → IF + CH₃ has been studied using classical trajectory methods on an extended L.E.P.S. surface with a well corresponding to the reaction intermediate CH₃IF, which is known to be a stable species. In the calculations the methyl group is treated as a structureless particle. The reaction is studied at two initial collisional energies, 11 and 46 kJ mol^–1, and values are obtained for the total reaction cross-section, differential cross-section and product energy disposal. In addition, the thermal rate coefficient at 298 K is calculated. The calculated results are compared with those from molecular-beam experiments. Good agreement is found between the experimental and calculated product translational energy distributions. The calculated reaction cross-sections decrease with increasing collisional energy, whilst the experimental values increase. This is attributed to the potential-energy surface being too attractive at long range. It is concluded from the angular scattering distributions that the surface incorrectly makes the most stable form of CH₃IF linear and that it must be bent. The neglect of the internal motion of the CH₃ does not allow calculation of the partitioning of the product internal energy between CH₃ and IF, and this may also affect the form of the angular scattering distributions.