Nonempirical Description of the Atmospherically Important Anionic Species. III. Hydrated Nitrogen Dioxide Anions

Neutral and negatively charged NO₂(H₂O)_n clusters are simulated at the second order of the Møller–Plesset perturbation theory with 6-31G basis set extended with diffuse and polarization functions on all nuclei. For better reliability, configuration interaction and multiconfiguration self-consistent field calculations with the active spaces, formed by all single and double excitations to the basic determinant, are carried out. The weak binding of a neutral NO₂ molecule to water clusters is provided by its coordination to two water molecules, either directly H bonded to each other or joined in an H-bond network via the third molecule. The presence of an excess electron strongly decreases the summary energy of the NO₂(H₂O)_n system, so that its adiabatic affinity exceeds the summary affinity of NO₂ and water system, although the excess electron is localized predominantly by NO₂ fragment.