OH^• + HCl Reaction at the Surface of a Water Droplet: An Ab Initio Molecular Dynamical Study

The Born-Oppenheimer molecular dynamics (BOMD) simulation has been performed to investigate the dynamics of the OH^• + HCl reaction at the surface of a water droplet. The investigation suggests that the reaction occurred at the surface of the water droplet becomes almost 10 times faster than the corresponding gas-phase reaction. Besides, we have also performed the quantum mechanics/molecular mechanics calculation to calculate the unimolecular energy barrier of the reaction. The results indicate that the barrier height gets decreased by ∼0.3 kcal mol^-1 at the surface of the water droplet, which also justifies the rate enhancement suggested by the BOMD simulation. The BOMD simulation also indicates that, at equilibrium, the product Cl^• forms four hydrogen bonds with four interfacial water molecules, which stabilize the Cl^• and resist it to escape from the surface.