Classical trajectory study of the orientation dependence of the reaction CH3I+K→KI+CH3

Using the three-body approximation for the subject reaction (taking CH3 to be a structureless particle), a potential energy surface has been constructed to encompass the key features of the observed reaction dynamics. To accommodate the inference from the existing experimental data on the dependence of the reaction probability upon the ‘‘angle of attack’’ γ the potential energy surface has an orientation-dependent barrier which increases essentially linearly with cos γ from threshold up to a cut-off angle γ∼130° corresponding to a 50° steric cone of nonreaction. Classical trajectory calculations of the reaction cross section σR at collision energies from threshold to 0.14 eV show a strong orientation dependence, with dσR/d cos γ decreasing nearly linearly with cos γ to the energy-dependent cut-off angle predicted from the standard angle-dependent barrier models. The relation between such a calculated orientational opacity function and experimental data on the dependence of the cross section upon the initial angle of attack is evaluated and implications for future experiments employing oriented molecule beams discussed.