On the ion-pair dissociation mechanisms in the small NaCl·(H O) cluster: A perspective from reaction path search calculations.

We performed reaction path search calculations for the NaCl·(H O) cluster using the global reaction route mapping (GRRM) code to understand the atomic-level mechanisms of the NaCl → Na  + Cl ionic dissociation induced by water solvents. Low-lying minima, transition states connecting two local minima and corresponding intrinsic reaction coordinates on the potential energy surface are explored. We found that the NaCl distances at the transitions states for the dissociation pathways were distributed in a relatively wide range of 2.7-3.7 Å and that the NaCl distance at the transition state did not correlate with the commonly used solvation coordinates. This suggests that the definition of the transition states with specific structures as well as good reaction coordinate is very difficult for the ionic dissociation process even in a small water cluster. © 2018 Wiley Periodicals, Inc.