Imaging Reaction Dynamics of F-(H2O) and Cl-(H2O) with CH3I.

The dynamics of microhydrated nucleophilic substitution reactions have been studied using crossed beam velocity map imaging experiments and quasiclassical trajectory simulations at different collision energies between 0.3 and 2.6 eV. For F-(H2O) reacting with CH3I, a small fraction of hydrated product ions I-(H2O) is observed at low collision energies. This product, as well as the dominant I-, is formed predominantly through indirect reaction mechanisms. In contrast, a much smaller indirect fraction is determined for the unsolvated reaction. At the largest studied collision energies, the solvated reaction is found to also occur via a direct rebound mechanism. The measured product angular distributions exhibit an overall good agreement with the simulated angular distributions. Besides nucleophilic substitution, also ligand exchange reactions forming F-(CH3I) and, at high collision energies, proton transfer reactions are detected. The differential scattering images reveal that the Cl-(H2O) + CH3I reaction also proceeds predominantly via indirect reaction mechanisms.