Mechanistic Insights into the Reactive Uptake of Bromine Nitrate at the Air–Water Interface: Interplay between Halogen Bonding and Solvation

Abstract

The reactive uptake of bromine nitrate (BrONO₂) into aqueous aerosols is a pivotal process in atmospheric bromine chemistry. BrONO₂ forms halogen bonds with adjacent water molecules, disrupting hydrogen-bond networks and potentially triggering unique chemical behaviors. However, the role of halogen bonds in interfacial reactions remains an open question. Herein, we employ a comprehensive approach combining quantum chemistry calculations, classical molecular dynamics, ab initio molecular dynamics (AIMD) simulations, and advanced enhanced sampling methods to investigate the solvation and hydrolysis of bromine nitrate (BrONO₂) at the air–water interface. Our simulations reveal that BrONO₂ can stably exist at the interface, providing favorable conditions for its hydrolysis. The interplay between halogen bonding and solvation facilitates the spontaneous formation of H₂OBrONO₂ at the interface, which subsequently reacts to produce HOBr and HNO₃. Free energy calculations indicate that this reaction is both kinetically and thermodynamically favorable at the air–water interface with an energy barrier of approximately 3.0 kcal/mol at 300 K. The insights from this simulation study will help guide future experiments to explore how water clouds affect halogen chemistry.