Ab Initio Investigations of Stable Geometries of the Atmospheric Negative Ion NO₃⁻(HNO₃)₂ and Its Monohydrate

Abstract

The possible stable geometries of the atmospheric negative core ion ${\text{NO}}_{3}^{ - }\left({{\text{HNO}}_{3} } \right)_{2}$ and its monohydrate were theoretically investigated with the second order Møller-Plesset perturbation theory (MP2) in consideration of the effect of electron correlation. For both ionic clusters, we obtained the different stable geometries from the previous study by Drenck and coworkers (Int J Mass Spectrom 273:126–131, 2008) [1] with the density functional theory of Becke 3-parameters hybrid functional (B3LYP). The non-planar geometry with two hydrogen-bondings between one oxygen atom on ${\text{NO}}_{3}^{ - }$ and each hydrogen atom of two HNO₃ fragments is found as the most stable structure of the core ion at 0 K. For the monohydrate, the most stable geometry at 0 K is found as the H ₂ O-embedded form in which one water molecule is located at the center of the cluster with hydrogen-bondings to ${\text{NO}}_{3}^{ - }$ and HNO₃ fragments. Our results show that the hydrogen bond network of the core ion can be strongly perturbed by a single water molecule. We also discussed the relative abundance of conformers of these ionic clusters under a finite temperature.