Abstract：
The chemistry of sulfur cycle contributes significantly to the atmospheric nucleation process, which is the first step of new particle formation (NPF). In the present study, cycloaddition reaction mechanism of sulfur trioxide (SO3) to hydrogen sulfide (H2S) which is a typical air pollutant and toxic gas detrimental to the environment were comprehensively investigate through theoretical calculations and Atmospheric Cluster Dynamic Code simulations. Gas-phase stability and nucleation potential of the product thiosulfuric acid (H2S2O3, TSA) were further analyzed to evaluate its atmospheric impact. Without any catalysts, the H2S + SO3 reaction is infeasible with a barrier of 24.2 kcal/mol. Atmospheric nucleation precursors formic acid (FA), sulfuric acid (SA), and water (H2O) could effectively lower the reaction barriers as catalysts, even to a barrierless reaction with the efficiency of cis-SA > trans-FA > trans-SA > H2O. Subsequently, the gas-phase stability of TSA was investigated. A hydrolysis reaction barrier of up to 61.4 kcal/mol alone with an endothermic isomerization reaction barrier of 5.1 kcal/mol under the catalytic effect of SA demonstrates the sufficient stability of TSA. Furthermore, topological and kinetic analysis were conducted to determine the nucleation potential of TSA. Atmospheric clusters formed by TSA and atmospheric nucleation precursors (SA, ammonia NH3, and dimethylamine DMA) were thermodynamically stable. Moreover, the gradually decreasing evaporation coefficients for TSA-base clusters, particularly for TSA-DMA, suggests that TSA may participate in NPF where the concentration of base molecules are relatively higher. The present new reaction mechanism may contributes to a better understanding of atmospheric sulfur cycle and NPF.
摘要：
硫循环的化学性质大大有助于大气成核过程，这是新粒子形成(NPF)的第一步。在本研究中,通过理论计算和大气集群动态代码模拟，全面研究了三氧化硫（SO3）与硫化氢（H2S）的环加成反应机理，硫化氢是一种典型的空气污染物和对环境有害的有毒气体。进一步分析了产物硫代硫酸（H2S2O3，TSA）的气相稳定性和成核潜力，以评估其对大气的影响。没有任何催化剂,H2S+SO3反应在24.2kcal/mol的势垒下是不可行的。大气成核前体甲酸(FA)，硫酸（SA），和水（H2O）可以有效地降低反应壁垒作为催化剂，甚至可以进行无阻碍的反应，其效率为顺式SA>反式FA>反式SA>H2O。随后，研究了TSA的气相稳定性。在SA的催化作用下，单独的水解反应屏障高达61.4kcal/mol，吸热异构化反应屏障为5.1kcal/mol，证明了TSA的足够稳定性。此外，进行拓扑和动力学分析以确定TSA的成核潜力。由TSA和大气成核前体形成的大气团簇(SA，氨NH3和二甲胺DMA）是热力学稳定的。此外，TSA基簇的蒸发系数逐渐减小，特别是对于TSA-DMA，表明TSA可能参与基础分子浓度相对较高的NPF。目前的新反应机理可能有助于更好地理解大气硫循环和NPF。
