Translational energy dependence of product energy and angular distribution for the K + CH3I reaction

Molecular beam scattering (velocity-analysis) experiments have been carried out for the now-classic “rebound” reaction K + CH3I → KI + CH3 over a range of relative translational energies text-decoration:overlineET from 0.077 to 0.16 eV. Detailed centre-of-mass differential reaction cross sections have thereby been obtained (at three energies), showing the expected predominant “back-scattering” of the fast-recoiling KI product. There is very little coupling between the angular and recoil energy distributions. The differential solid-angle cross section peaks at 180°(with a half-angle close to 90°) with shape essentially independent of text-decoration:overlineET over the range of the experiments. The distribution of final translational energy ET′ is rather sharp, showing a peak at about 60 % of the total available energy. The average recoil energy text-decoration:overlineET′ increases with text-decoration:overlineET.These results are combined with previous experimental findings from this laboratory on the CH3I–K, —Rb reactions (the “alignment effect” and the ET-dependence of the total reaction cross section), and compared with observations of other groups. A current, overall, experimental summary is presented, to serve as a target for theory.