Gas-Phase Photolysis of Hg(I) Radical Species: A New Atmospheric Mercury Reduction Process

The efficient gas-phase photoreduction
of Hg­(II) has recently been
shown to change mercury cycling significantly in the atmosphere and
its deposition to the Earth’s surface. However, the photolysis
of key Hg­(I) species within that cycle is currently not considered.
Here we present ultraviolet–visible absorption spectra and
cross-sections of HgCl, HgBr, HgI, and HgOH radicals, computed by
high-level quantum-chemical methods, and show for the first time that
gas-phase Hg­(I) photoreduction can occur at time scales that eventually
would influence the mercury chemistry in the atmosphere. These results
provide new fundamental understanding of the photobehavior of Hg­(I)
radicals and show that the photolysis of HgBr increases atmospheric
mercury lifetime, contributing to its global distribution in a significant
way.

近期研究表明，高效气相汞（II）的光化学还原作用显著改变了大气中汞的循环及其对地球表面的沉积。然而，在该循环中关键汞（I）物种的光解作用尚未得到考虑。本研究通过高级量子化学方法计算了HgCl、HgBr、HgI和HgOH自由基的紫外-可见吸收光谱和截面，并首次揭示了气相汞（I）的光化学还原作用能够在最终影响大气中汞化学的时间尺度上发生。这些结果为汞（I）自由基的光学行为提供了新的基本理解，并显示HgBr的光解作用能够延长大气中汞的寿命，从而以显著的方式影响着其全球分布。