Element sulfur has proven to be active material for hazardous elemental mercury (Hg⁰) removal. However, the underlying mechanism of elemental sulfur reacting with Hg⁰ was still unclear. Generally, solid elemental sulfur exists mainly composed of crown-shaped S₈ molecules and traces of S₆, S₇, and S₉ molecules. This research employed quantum chemical calculations and electronic wavefunction analysis to investigate the reaction between branched and cyclic S_n isomers (n=6-9) with Hg⁰ at the molecular level. Thermodynamic data and kinetics were also computed. It was found that Hg⁰ react with branched S_n isomers would proceed spontaneously with heat release by analyzing reaction Gibbs free energies and enthalpies. Reaction rate constants of branched S_n molecules are several orders of magnitude higher than those of cyclic S_n molecules. Moreover, the electronic wavefunction analysis was conducted. The Mayer bond order along the reaction pathway could characterize Hg-S and S-S bonds breaking and formation quantitively. Localized molecular orbitals isosurface maps reflect Hg-S bonds show typical $\sigma$ bond characteristics in the products. Localized orbital locator color-filled maps reveal electrons begin to concentrate in the region between Hg and S atoms as reactions proceeding forward. In summary, this research would help develop sulfur contained adsorbents with superior Hg⁰ removal performance in the future.

元素硫已被证明是用于除去有害元素汞（Hg ⁰）的活性材料。但是，元素硫与Hg ⁰反应的潜在机理仍不清楚。通常，固态元素硫主要由冠状的S ₈分子和痕量的S ₆，S ₇和S ₉分子组成。这项研究利用量子化学计算和电子波函数分析研究了Hg ⁰在分子水平上的支链和环状S _n异构体（n = 6-9）的反应。还计算了热力学数据和动力学。发现Hg ⁰与支链S反应通过分析反应吉布斯自由能和焓，_n个异构体会自发释放热量。支链S _n分子的反应速率常数比环状S _n分子的反应速率常数高几个数量级。此外，进行了电子波函数分析。沿着反应路径的Mayer键顺序可以定量表征Hg-S和SS键的断裂和形成。局部分子轨道等值面图反映Hg-S键显示典型$\sigma$产品的粘结特性。局部轨道定位器的彩色填充图显示，随着反应的进行，电子开始集中在Hg和S原子之间的区域中。总而言之，这项研究将有助于将来开发出具有优异的Hg ⁰去除性能的含硫吸附剂。