Scientist at IQFR report in JACS UV-Vis absorption spectra and cross sections of gas-phase Hg(I) radicals. The results show for the first time that atmospheric photoreduction of Hg(I) radicals can occur.

Anthropogenic mercury emissions are primarily in the gaseous elemental form. In the atmosphere, mercury emissions oxidize to gaseous Hg(I) and Hg(II) compounds that are more soluble and deposited to eh surface by rain. Atmospheric reduction of mercury competes with deposition, thereby modifying the magnitude and pattern of Hg deposition. Previously, the photoreduction of Hg(II) has been shown to significantly influence the atmospheric mercury cycle. However, the photolysis of key Hg(I) species within that cycle is currently not considered. In this study, we use quantum-chemical methods to study potential energy curves, geometrical and thermochemical properties, and for the first time, absorption spectra and cross sections of gas-phase Hg(I) radicals. The new photochemistry of Hg(I) radicals has broad implications for the atmospheric mercury cycle such as increasing atmospheric mercury lifetime, contributing to its global distribution in a significant way.

Alfonso Saiz-Lopez, A. Ulises Acuña, Tarek Trabelsi, Javier Carmona-García, Juan Z. Dávalos, Daniel Rivero, Carlos A. Cuevas, Douglas E. Kinnison, Sebastian P. Sitkiewicz, Daniel Roca-Sanjuán and Joseph S. Francisco. Gas-phase photolysis of Hg(I) radical species: A new atmospheric mercury reduction process. Journal of the American Chemical Society. DOI: 10.1021/jacs.9b02890, 2019.