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.