SN2 Reactions of N2O5 with Ions in Water: Microscopic Mechanisms, Intermediates, and Products

Dinitrogen pentoxide (N2O5) is an extremely important species in the chemistry of the atmosphere. Reactions of N2O5 greatly affect, either directly or indirectly, the concentrations of NO3, ozone, OH radicals, methane, and more. Of great importance are the heterogeneous reactions with Cl– and other anions, but a microscopic understanding of these reactions is not yet at hand. In this work, we employ ab initio molecular dynamics (AIMD) and other tools of computational chemistry to explore reactions of N2O5 with anions hydrated by 12 water molecules, in order to shed light on this important class of reactions. The ions investigated are Cl–, SO42–, ClO4–, and RCOO– (R = H, CH3, C2H5). The following main results are obtained: (i) all the reactions take place with an SN2 type mechanism, with a transition state that involves a contact ion pair (NO2+NO3–) that interacts strongly with water molecules. (ii) Reactions of a solvent separated nitronium ion (NO2+) are not observed in any of the cases. (iii) Recent exp...