Molecular insights into thermally induced behavior of hydroxyl radicals at water nanodroplet interfaces.

Water nanodroplets act as microreactors, driving critical processes in atmospheric chemistry, pollutant degradation, and aerosol formation. This study utilizes ab initio molecular dynamics (AIMD) simulations to unravel the thermally induced behavior of hydroxyl (OH) radicals within water nanodroplets across temperatures ranging from 300 K to 400 K. Elevated temperatures significantly weaken the hydrogen-bonding network, enhance OH radical mobility, and promote interfacial reactivity. The energy barriers for hydrogen transfer events decrease from ~ 4 kcal/mol at 300 K to ~ 2.5 kcal/mol at 400 K, facilitating rapid migration of OH radicals from the droplet interior to the air-water interface. Thermal energy also induces droplet deformation, as reflected by an increase in the asphericity parameter, further amplifying interfacial dynamics. Despite these thermal perturbations, OH radicals maintain a consistent orientation at the interface, stabilized by interfacial forces and localized hydrogen bonding. These findings provide molecular-scale insights into temperature-dependent radical dynamics with broad implications for atmospheric oxidation, plasma-liquid interactions, and environmental chemistry.