On the gas-phase reaction between SO₂ and O₂⁻(H₂O)_0–3 clusters – an ab initio study

Abstract

We present an ab initio investigation of the gas-phase reaction between SO2 and a O2(-)(H2O)n molecular cluster, n = 0-3. The associative product cluster, O2SO2(-)(H2O)n, is formed with high energy gain although the binding energies decrease with increasing hydration. About 54 kcal mol(-1) may be gained by isomerization of O2SO2(-)(H2O)n to the sulfate radical, SO4(-)(H2O)n, but a high energy barrier separates the two states. Although the isomerization is catalysed by the presence of a second SO2 molecule, the formation of SO4(-)(H2O)nvia O2(-)(H2O)n and SO2 is found to be negligible under atmospheric conditions. At thermal equilibration at 298.15 K and 50% relative humidity the end products are mainly O2SO2(-) and O2SO2(-)(H2O)1.

Exploring the chemical fate of the sulfate radical anion by reaction with sulfur dioxide in the gas phase

“…The evaporation rate constant, k evap,(R4b) , is determined from the detailed balance condition (Vehkamäki, 2006;Ortega et al, 2012) as…”

A potential source of atmospheric sulfate from O<sub>2</sub><sup>−</sup>-induced SO<sub>2</sub> oxidation by ozone

“…This study highlights the role of the superoxide ions (O2 -) in SO2 oxidation. Our previous study demonstrated that SO2 interacts with O2and forms O2SOOwhose atmospheric fate remains unelucidated (Tsona et al, 2014). In this study, we used ab initio calculations to assess the chemical fate of O2SOOby collisions with O3.…”

A potential source of atmospheric sulfate from O<sub>2</sub><sup>−</sup>-induced SO<sub>2</sub> oxidation by ozone

“…The immediate products of SO 2 oxidation by ions are mostly sulfur oxide ion intermediates (Fehsenfeld and Ferguson, 1974;Möhler et al, 1992;Bork et al, 2012;Tsona et al, 2014) that are susceptible to the triggering of new reactions or recombination with oppositely charged counterparts to form neutral species. Some of these ions, namely SO − 3 , SO − 4 , and SO − 5 , were detected at relatively high concentrations in the ambient atmosphere (Ehn et al, 2010) and in chamber experiments of SO 2 ionic oxidation studies (Nagato et al, 2005;Hvelplund et al, 2013;Kirkby et al, 2011Kirkby et al, , 2016.…”

“…Reliable predictions of the outcomes of these ions require an exact knowledge of their chemical structures since interactions between molecules or ions depend both on their physical and chemical properties. A previous study demonstrated that two forms of SO − 4 separated by a high energy barrier may exist in the atmosphere (Tsona et al, 2014): the sulfate radical ion henceforth indicated as SO − 4 , and the peroxy form, O 2 SOO − , in which the O 2 S-OO − bond nature is more dative than covalent. Formerly, the two isomers were often misleadingly attributed exclusively to the sulfate radical ion, the most stable form of SO − 4 .…”

“…The formation mechanisms of SO − 4 in the gas phase have been largely unknown but, recent studies showed that this ion can be formed by SO − 5 reaction with O 3 (Bork et al, 2013) and in a O 2 SOO − isomerization process catalyzed by NO (Tsona et al, 2018). SO − 4 can also be produced during the chemical transformation of organic compounds, triggered by sulfate salts (Noziere et al, 2010), whereas O 2 SOO − is formed at collision rates upon SO 2 reaction with O − 2 (Fahey et al, 1982;Tsona et al, 2014).…”