Large nucleating ions (H2SO4)n(HSO4-)(NH3)m : Formation mechanism and appearance in the earth’s atmosphere.

Ammonium bisulfate (HSO₄^-)(NH₃) ion is extremely unstable thermodynamically. However, larger stable (H₂SO₄)n(HSO₄)(NH₃)m clusters have been observed in laboratory experiments under atmospherically relevant conditions. In the present paper, we investigate stabilization of (H₂SO₄)n(HSO₄^-)(NH₃)m clusters by NH₃ using the Density Functional Theory (DFT), discuss structural trends, elucidate the stabilization mechanism, report new thermochemical data and explore their implications. In particular, we show that stable (H₂SO₄)n(HSO₄^-)(NH₃)m clusters in the atmosphere are formed via addition of NH₃ to (H₂SO₄)n(HSO₄^-) at n >2 and that the most abundant (H₂SO₄)n(HSO₄^-)(NH₃)m ions contain one and two NH₃ molecules, respectively. [ABSTRACT FROM AUTHOR]