Structures of NO₂⁺(H₂O)<i>_n</i> and (HNO₃)(H₃O⁺)(H₂O)<i>_n</i>_-₂ (<i>n</i> = 2−4) Clusters

Abstract

The structures of more than thirty H₂<i>_n</i>NO<i>_n</i>₊₂⁺ (<i>n</i> = 2−4) complexes have been optimized in ab initio MP2/6-31+G* calculations. Relative energies of the species identified have been established in G2MP2 theoretical\ncalculations and applied to an examination of the thermochemistry of the NO₂⁺(H₂O)<i>_n</i>_-₁<b> + </b>H₂O → NO₂⁺ +\n(H₂O)<i>_n</i> → HNO₃(H₃O⁺)(H₂O)<i>_n</i>_-₂ → HNO₃ + H₃O⁺(H₂O)<i>_n</i>_-₂ reactions. The nature of the most stable cluster\nvaries with size. An ion-centered NO₂⁺(H₂O)₂ is the global minimum energy structure on the H₄NO₄⁺ surface,\nwhile an HNO₃(H₃O⁺)(H₂O)₂ complex is most stable on H₈NO₆⁺. On the H₆NO₅⁺ surface NO₂⁺(H₂O)₃, HNO₃(H₃O⁺)(H₂O) and H₂NO₃⁺(H₂O)₂ clusters lie within 1 kcal/mol of each other.