First results from the interaction between hydroxyl radicals and condensed water droplets: A spin-polarized DFT-MD study

Abstract

The formation of clouds results from condensation of water vapor into liquid water droplets. These water droplets form on the surface of tiny particles that are suspended in the air, like dust. Atmospheric chemistry relies heavily on the hydroxyl radical (OH*), which is highly reactive and prone to combining with hydrogen atoms in other compounds. Despite previous studies concerning liquid, solid, and gas phase interactions, how hydroxyl radicals interact with condensed water droplets is still unknown. OH*-condensed droplet interactions show unique behavior, according to our studies. Several hydrogen transfers were detected during the interaction process. It takes approximately 3.5 kcal/mol of energy to initiate hydrogen transfer. Moreover, we revealed the dominant structures of hydrated radicals during the mobility of OH* into condensed droplets using Born–Oppenheimer molecular dynamics simulations. In contrast to our previous studies, the hemibond doesn't significantly affect the stability of OH*(H2O)n structures in condensed droplets. Our results showed that condensed droplets hinder the mobility of OH*, causing its diffusion coefficient to decrease. Moreover, several analyses were carried out to investigate condensed droplet surfaces, bonding patterns, and the position of OH* in conjunction with water molecules, including mobility analyses, radial distribution functions, coordination analyses, and population analyses.