Donaldson D James, Kroll Jay A, Vaida Veronica
Department of Chemistry, University of Toronto, Toronto, ON Canada.
Department of Physical and Environmental Sciences, University of Toronto, ON Canada.
Sci Rep. 2016 Jul 15;6:30000. doi: 10.1038/srep30000.
Sulfur chemistry is of great interest to the atmospheric chemistry of several planets. In the presence of water, oxidized sulfur can lead to new particle formation, influencing climate in significant ways. Observations of sulfur compounds in planetary atmospheres when compared with model results suggest that there are missing chemical mechanisms. Here we propose a novel mechanism for the formation of sulfurous acid, which may act as a seed for new particle formation. In this proposed mechanism, the lowest triplet state of SO2 ((3)B1), which may be accessed by near-UV solar excitation of SO2 to its excited (1)B1 state followed by rapid intersystem crossing, reacts directly with water to form H2SO3 in the gas phase. For ground state SO2, this reaction is endothermic and has a very high activation barrier; our quantum chemical calculations point to a facile reaction being possible in the triplet state of SO2. This hygroscopic H2SO3 molecule may act as a condensation nucleus for water, giving rise to facile new particle formation (NPF).
硫化学对于多个行星的大气化学具有重大意义。在有水存在的情况下，氧化态的硫会导致新粒子的形成，对气候产生重大影响。将行星大气中硫化合物的观测结果与模型结果相比较，结果表明存在缺失的化学机制。在此，我们提出一种形成亚硫酸的新机制，亚硫酸可能充当新粒子形成的种子。在这个提出的机制中，二氧化硫的最低三重态（(3)B1），它可以通过近紫外太阳辐射将二氧化硫激发到其激发态(1)B1，随后快速系间窜越而获得，在气相中直接与水反应形成亚硫酸。对于基态二氧化硫，该反应吸热且具有非常高的活化能垒；我们的量子化学计算表明，在二氧化硫的三重态下可能发生容易进行的反应。这种具有吸湿性的亚硫酸分子可能充当水的凝结核，从而导致新粒子的轻易形成（NPF）。
