Department of Chemistry, University of Toronto, 80 Saint George Street, Toronto, Ontario, Canada M5S 3H6.
J Phys Chem A. 2010 Feb 11;114(5):2164-70. doi: 10.1021/jp9085156.
The ozonation of dissolved sulfur dioxide is an important route for sulfate formation, especially in fog and cloud droplets of high pH. However, little is known about the detailed chemical mechanism of this process. We have mapped out the fate of aqueous SO(2) in the presence of ozone by use of density functional theory (DFT) calculations in solution (via the polarized continuum model, PCM), including up to two explicit water molecules. The calculations predict that the hydrolysis of SO(2).H(2)O, although possessing a barrier, is still more energetically favorable than its ozonation. The ozonation of HOSO(2)(-) and SO(3)(2)(-) proceeds without barriers and gives S(VI) products that are more stable than the reagents by 77.1 and 88.6 kcal/mol, respectively. By comparing our calculated pH dependence of the ozonation kinetics to those determined experimentally, we conclude that, despite a high calculated energy barrier to the ozonation of sulfonate (HSO(3)(-)), it is the dominant form of S(IV) in solutions of neutral pH and is the species through which ozonation occurs.
溶解的二氧化硫的臭氧化是硫酸盐形成的重要途径，特别是在高 pH 值的雾和云滴中。然而，人们对这一过程的详细化学机制知之甚少。我们通过在溶液中使用密度泛函理论 (DFT) 计算（通过极化连续模型，PCM），包括多达两个显式水分子，描绘了臭氧存在下水溶液中 SO(2)的命运。计算预测，尽管 SO(2).H(2)O 的水解具有障碍，但它仍然比臭氧化更具能量优势。HOSO(2)(-) 和 SO(3)(2)(-) 的臭氧化没有障碍，并且生成的 S(VI)产物比试剂分别稳定 77.1 和 88.6 kcal/mol。通过将我们计算的臭氧动力学的 pH 依赖性与实验确定的进行比较，我们得出结论，尽管硫酸盐（HSO(3)(-))的臭氧化具有很高的计算能垒，但它是中性 pH 溶液中 S(IV)的主要形式，是臭氧发生的物种。
