Computational Study on the Photolysis of BrHgONO and the Reactions of BrHgO with CH, CH, NO, and NO: Implications for Formation of Hg(II) Compounds in the Atmosphere.

Global models suggest BrHgONO to be the major Hg(II) species initially formed in atmospheric oxidation of Hg(0) in most of the atmosphere, but its atmospheric fate has not been previously investigated. In the present work, we use quantum chemistry to predict that BrHgONO photolysis produces the thermally stable radical BrHgO. Subsequently, BrHgO may react with NO to form thermally stable BrHgONO, or with NO to re-form BrHgONO. Additionally, BrHgO abstracts hydrogen atoms from CH and CH with higher rate constants than does OH, producing a stable BrHgOH molecule. Because BrHgO can abstract hydrogen atoms from sp-hybridized carbons on many organic compounds, we expect production of BrHgOH to dominate globally, although formation of BrHgONO and BrHgONO may compete in urban regions. In the absence of experimental data on the kinetics and fate of BrHgONO and BrHgO, we aim to guide modelers and other scientists in their search for Hg(II) compounds in the atmosphere.