Ab initio and analytical intermolecular potential for ClO–H2O

Communication: Interaction of BrO radical with the surface of water

Solvation of a BrO radical in a slab of water is investigated using adaptive buffered force quantum mechanics/molecular mechanics (QM/MM) dynamics simulations. The simulation results show that the BrO radical exhibits preference towards the water surface with respect to the interior region of the water slab, despite BrO's high affinity to water. Another important finding is the weakening of (BrO)Br⋯O(water) interaction at the water surface due to competitive interactions between (BrO)Br⋯O(water) and (water)H⋯O(water). As such, the BrO-water slab interaction is dominated by (BrO)O⋯H(water) interaction, contrary to that in the gas phase, suggesting that the reactive site for the BrO radical at the air/water surface is more likely the Br site. The conclusion from this study can offer deeper insight into the reactivity of the BrO radical at the air/water interface, with regard to atmospheric implications.

Analytic ab initio-based molecular interaction potential for the BrO⋅H2O complex

Radical halogen oxide species play important roles within atmospheric processes, specifically those responsible for the removal of O3. To facilitate future investigations on this family of compounds, RCCSD(T)/aug-cc-pVQZ-level electronic structure calculations were employed to generate individual-molecule optimized geometries, as well as to determine the global minimum energy structure for the BrO⋅H2O complex. This information facilitated the generation of several one-dimensional potential energy surface (PES) scans for the BrO⋅H2O complex. Scans were performed for both the ground state and the first excited state; this inclusion is due to a low-lying first electronic excited-state energy. These rigid-geometry PES scans were used both to generate a novel analytic interaction potential by modifying the existing Thole-type model used for water and to the fitted potential function. This interaction potential features anisotropic atomic polarizabilities facilitating appropriate modeling of the physics regarding the unpaired electron residing within the p-orbitals of the oxygen atom of the bromine oxide radical. The intention of this work is to facilitate future molecular dynamics simulations involving the interaction between the BrO radical and water clusters as a first step in devising possible novel chemistries taking place at the water interface of clouds within the atmosphere.