Suppression of low product kinetic energies in reactions of FHO− and Cl−(H2O) with CH3I

Abstract

Substantially different reaction dynamics, product branching ratios and time scales have been reported in crossed beam imaging experiments on the nucleophilic substitution reactions of Cl−(H2O) and F−(H2O) with CH3I at 0.3 eV collision energy [Bastian et al., J. Phys. Chem. A 124, 1929 (2020)]. In particular, it was speculated that Cl−(H2O) only undergoes nucleophilic substitution via a ligand exchange intermediate. Here, we present crossed-beam scattering results for the two title reactions that both show a suppression of low product kinetic energies. We discuss this mechanism in comparison with recent results on the ligand exchange in F−(H2O) + CH3I collisions. This also allows for a more detailed picture of the dynamics of hydrated nucleophilic substitution reactions at low collision energy.