Reaction dynamics of the methoxy anion CH 3 O - with methyl iodide CH 3 I.

Studying larger nucleophiles in bimolecular nucleophilic substitution (S N 2) reactions bridges the gap from simple model systems to those relevant to organic chemistry. Therefore, we investigated the reaction dynamics between the methoxy anion (CH 3 O - ) and iodomethane (CH 3 I) in our crossed-beam setup combined with velocity map imaging at the four collision energies 0.4, 0.7, 1.2, and 1.6 eV. We find the two ionic products I - and CH 2 I - , which can be attributed to the S N 2 and proton transfer channels, respectively. The proton transfer channel progresses in a previously observed fashion from indirect to direct scattering with increasing collision energy. Interestingly, the S N 2 channel exhibits direct dynamics already at low collision energies. Both the direct stripping, leading to forward scattering, and the direct rebound mechanism, leading to backward scattering into high angles, are observed.