Hoo ~, (sub) Sulfuric Acid Molecule Coupling Mechanism And Its Radicals Complex Capture Of The Electron Theory

Hydroperoxyl radical (HOO·) is an important active species in atmospheric chemical reactions, which participates in various physical and chemical reaction processes. Especially, HOO·participates in the ozone depletion in the atmosphere. Recently, much attention has been paid to the elimination or uptake of the HOO·radical experimentally and theoretically.In the present study, we have systematically investigated the mechanism of the uptake of the HOO·radical by the atmospheric molecules and the dynamically process of the formation of HOOH from HOO·radical using density functional theory, atoms in molecules (AIM) theory, the natural bond orbital (NBO) method, and energy decomposition analyses (EDA). In details, the H2SO3…HOO·and H2SO4…HOO·…(H2O)n(n=0-2) systems have been employed to better understand the process of the uptake of hydroperoxyl radical by the sulfurous acid and sulfuric acid aerosol. Moreover, the dynamically process of the electron capture behaviors of H2SO4…HOO·complex have also been studied to better understand the chemical conversion process after the uptake of HOO·radical by sulfuric acid aerosol.Three aspects are investigated systematically in the present study:Firstly, the nature of the coupling interactions between sulfurous acid and HOO·radical has been systematically investigated. As a result, eight stable stationary points possessing double H-bonding features have been located on the H2SO3…HOO·potential energy surface. The larger interaction energies of -12.27 and -11.72 kcal/mol are observed for the two most stable complexes, where both of them possess strong double intermolecular H-bonds of partial covalence. Furthermore, the energy decomposition analyses suggest that the interaction between H2SO3 and HOO·are predominated by both the electrostatic and orbital interactions. Additionally, the characteristics of the IR spectra for the two most stable complexes are discussed to provide some help for their possible experimental identification.Second, the coupling interactions among sulfuric acid (H2SO4), the hydroperoxyl radical (HOO·), and water molecules (H2O) have been studied detailedly, which is crucial for the better understanding of the role of the water molecules in the uptake of HOO·radicals by sulfuric acid aerosols at different atmospheric humidities. The equilibrium structures, binding energies, equilibrium distributions, and the nature of the coupling interactions in H2SO4…HOO·…(H2O)n(n=0-2) clusters have been systematically investigated. Two binary, five ternary, and twelve tetramer clusters possessing multiple intermolecular H-bonds have been located on their potential energy surfaces. Two different modes for water molecules have been observed to influence the coupling interactions between H2SO4 and HOO·through the formations of intermolecular H-bonds with or without breaking the original intermolecular H-bonds in the binary H2SO4…HOO·cluster. It has been found that the introduction of one or two water molecules can efficiently enhance the interactions between H2SO4 and HOO*, implying the positive role of water molecules in the uptake of the HOO·radical by sulfuric acid aerosols. Furthermore, the coupling interaction modes of the most stable clusters under study have been verified by the ab initio molecular dynamics.Finally, the electron capture behaviors of H2SO4…HOO·complex have been systematically investigated employing the MP2 and B3LYP methods in combination with ab initio molecular dynamics. It has been found that the electron capture process is a favorable reaction thermodynamically and kinetically. The excess electron can be captured by the HOO·fragment initially, and then the proton of H2SO4 fragment associated with the intermolecular H-bonds is transferred to HOO·fragment without any activation barriers, resulting in the formation of the HOOH species directly. Therefore, the electron capture process of the H2SO4…HOO·complex provides an alternative source of HOOH in the atmosphere. Moreover, the nature of the coupling interactions in the electron capture products has been clarified. At the same time, the most stable anionic complex has also been determined among the three anion complexes. Additionally, the influences of the adjacent water molecules on the electron capture properties have been investigated. The IR spectrum of the most stable electron capture product has been simulated to provide the direct proof of the formation of the HOOH experimentally.