Imaging the Atomistic Dynamics of Single Proton Transfer and Combined Hydrogen/Proton Transfer in the O– + CH3I Reaction

We report on reactive scattering studies of the proton transfer and combined hydrogen/proton transfer in the O– + CH3I reaction. We combine state-of-the-art crossed-beam velocity map imaging and quantum chemistry calculations to understand the dynamics for the formations of the CH2I– + OH and CHI– + H2O products. The experimental velocity- and angle-differential cross section show for both products and at all collision energies (between 0.3 and 2.0 eV) that the product ions are predominantly forward scattered. For the CHI– + H2O channel, the data show lower product velocities, indicative of higher internal excitation, than in the case of single proton transfer. Furthermore, our results suggest that the combined hydrogen/proton transfer proceeds via a two-step process: In the first step, O– abstracts one H atom to form OH–, and then the transient OH– removes an additional proton from CH2I to form the energetically stable H2O coproduct.