Cl- + CH3I --> ClCH3 + I- SN2 Reaction Dynamics
This study is part of a research collaboration with The Roland Wester research group, University of Innsbruck, Austria. Both direct and indirect reaction mechanisms are observed in the trajectories. The direct reaction occurs by either the traditional SN2 rebound mechanism with Cl- colliding backside with direct displacement of I- and backward scattering, or by a stripping mechanism with forward scattering for which Cl- strips CH3 from the I-atom.  The indirect reaction may occur via a CH3 rotation, roundabout mechanism in which Cl- strikes the CH3-moiety causing it to rotate around the I-atom and Cl- displacing I- after one CH3 revolution with the backside of the CH3-moiety positioned next to Cl-. A small fraction of this indirect reaction occurs via multiple CH3 revolutions. At low collision energies indirect reaction with Cl----CH3I pre-reaction complex formation becomes important. The following are animations of representative trajectories for the above mechanisms, for collisions with a relative translational energy of 1.9, 0.39, or 0.20 eV, a CH3I rotational and vibrational temperature of 300K and an impact parameter of 0.5 Å.
Indirect reaction with one CH3 rotation:
Indirect reaction with two CH3 rotations:
Indirect reaction with pre-reaction complex flormation:
Non-reactive with formation of both pre-reaction and post-reaction complexes, and barrier recrossing: