A new insight into the interaction of hydroxyl radical with supercooled nanodroplet in the atmosphere

Abstract

• The interaction between OH* and supercooled nanodroplet led to delocalized states caused by surface effects. • The OH* shows a high tendency for accepting H-bond from neighboring water molecules around (1.77 Å, 122°). • RDF and ring analysis results confirmed the LDA ice for OH*-supercooled nanodroplet. • The preference of six-membered rings in supercooled nanodroplet based on ring analysis. • The 3-fold and 4-fold coordination were revealed as dominant structures. Fallstreak clouds are types of clouds with supercooled water droplets, meaning that they are still liquid at sub-freezing temperatures. In the atmosphere, hydroxyl radicals serve as an important source of oxidants. The reactivity of the hydroxyl radicals in ice environments is significant, affecting other atmospheric reactions. However, the interaction between OH radical with supercooled water nanodroplet remains unknown. This work presents a comprehensive computational study of OH radicals at the air-ice interface. Ab initio molecular dynamics simulation showed that despite previous assumptions, the hemibond could also exist in large OH*-nanodroplet systems under supercooling process. Two hydrogen-bonded water molecules along with the hemibond have been found to be the reason for OH* stability. There is a significant correlation between our RDF and ring analysis results and the structural information from X-ray crystallography, confirming LDA ice for supercooled nanodroplets. The hydrogen bond analysis revealed that there is no radical effect on the hydrogen bond formation of water nanodroplets at 250 K. Moreover, the time evolution of critical bonds based on distances revealed that the OH* could be a movable and reactive radical during the supercooling process. Results from this research contribute to a better understanding of natural phenomena and rational design of anti-icing systems for aviation, wind energy, and infrastructures along with cryopreservation.