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.