Ab Initio Molecular Dynamics Study Of OH Radical At Air-Water Interface

The hydroxyl radical plays a crucial role in chemical processes,especially in the earth's atmosphere.It can form some complexes with other atmospheric constituents,like water molecules through forming hydrogen bonds or hemibond.Previous ab-initio molecular dynamics studies on liquid phase systems have shown the existence of hemibond in OH*.However,the details of the OH radical(OH*)interaction in the atmospheric environment have not yet been fully determined.The possibility of diffusion hydroxyl radical in the atmosphere and prediction of its mobility mechanism is largely unknown.In this work,we considered various nanodroplets in atmospheric condition.Our findings indicate how an OH radical tends to move towards exterior layers of nanodroplet.Our research on OH*in atmospheric condition led to new structures and new mobility mechanism of OH*compared with previous discovered structures in aqueous solution.The high nucleation rate of supercooled water to ice makes some difficulties in the experimental investigation of OH radical in the atmosphere.In addition to regular cluster structures,ice also can exist in amorphous forms so that this issue creates some difficulties in the simulation of OH*(H2O)n specially in nanodroplets due to their special shapes.For this purpose,we considered some nanodroplets including one OH*placed on the nanodroplet in two different ice phases to investigate the spatial structure of hydrated OH*in the first solvation shell of iced-nanodroplet.Moreover,to understand the underlying freezing process of hydrated hydroxyl radical in amorphous forms of nanodroplet,three different systems were investigated under adjusting temperature in two consecutive cycles.The first chapter of this dissertation focuses on the aerosol particles in atmosphere and role of some radical-water complexes in atmosphere processes.The 2nd chapter provides an overview of molecular electronic structure computations specially the BORN-OPPENHEIMER approximation as ab-initio molecular dynamics methods.Chapter 3 focuses on cloud droplets and affection of droplet size on the processes in accommodation area.In chapter 4 we have shown the previous results of OH radical during interaction with water molecules namely in liquid phase.In chapter 5 we reported the results of OH radical in nanodroplet under atmospheric condition,where we showed how OH radical tends to outer layers.Chapter 6 and 7 focused on freezing process of water droplet to ice with considering different systems along with investigation of spatial structures of hydrated OH radical in the first solvation shell.