Abstract
New particle formation is an important source of atmospheric aerosols, but the nucleation phenomena is still poorly understood. Here the formation of bimolecular complexes of HOOO• radical with H2O, CH3NH2, HCOOH and H2SO4 has been investigated by quantum chemical methods. The stabilising effect of methylamine is found to be close to that of sulphuric acid, both complexes are formed spontaneously at studied atmospheric conditions. In addition, the hydration of the four most stable 1:1 complexes forming the 1:1:1 complexes have been considered. Water stabilises a HOOO•…H2SO4 complex, the most effectively. Complexation process is spontaneous as well. Complex formations induced significant red-shift and enhancement of the IR intensity for the OH stretching vibration relative to that of the free radical. Equilibrium constants have been examined and the relative abundance of complexes in the troposphere is discussed.
Highlights
Hydrotrioxy (HOOO) radical, or hydridotrioxygen according to IUPAC nomenclature,[1] belongs to the group of polyoxides with general molecular formula, ROnR, where R stands for hydrogen, any other atom or chemical group and n ≥ 3.2,3 It is believed that such polyoxides, especially the HOOO radical, play an important role in atmospheric processes in Earth’s troposphere and environmental reactions as well as in biological oxidation reactions.[4]
Nucleation is enhanced by organic compounds, formic acid is an important trace constituent of the troposphere.[18]. The abundance of these species varies, but experimental data proposes that the concentration of sulphuric acid and methylamine is hovering around 1 × 107 molecule cm–3 18,20, while a concentration of formic acid is higher, around 2 × 1011 molecule cm–3 18
Let us first consider the HOOO radical, the optimised structures of cis and trans conformations denoted as c-HTO and t-HTO, respectively, are presented in Figure 1 with the atom enumeration
Summary
Hydrotrioxy (HOOO) radical, or hydridotrioxygen according to IUPAC nomenclature,[1] belongs to the group of polyoxides with general molecular formula, ROnR, where R stands for hydrogen, any other atom or chemical group and n ≥ 3.2,3 It is believed that such polyoxides, especially the HOOO radical, play an important role in atmospheric processes in Earth’s troposphere and environmental reactions as well as in biological oxidation reactions.[4]. Water is the most abundant species in the atmosphere, its concentration varies between 1–4 %17, and can form strong hydrogen bonds with other molecules and radical species Such interactions can lead to the formation of new atmospheric particles that serve as a predecessors of secondary aerosols.[18,19] In addition to the water, sulphuric acid is the main molecular species in new particle formation.[19] Many recent studies reported the importance of gaseous amines (especially methyl-, dimethyl- and trimethylamine) in nucleation processes.[16] Nucleation is enhanced by organic compounds, formic acid is an important trace constituent of the troposphere.[18] The abundance of these species varies, but experimental data proposes that the concentration of sulphuric acid and methylamine is hovering around 1 × 107 molecule cm–3 18,20, while a concentration of formic acid is higher, around 2 × 1011 molecule cm–3 18. In this equation σ is the symmetry number, R is the universal gas constant, T is the temperature, NA is the Avogadro’s number and ΔGT is the complex formation Gibbs free energy change
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