Ab initio study of the stepwise hydration of NO⁺

The structure of NO⁺-H₂O is determined by ab initio calculations, in an extended polarized basis set supplemented by the dispersion energy, to be an angular adduct. The hydration energy of 21.92 kcal/mole compares well with the experimental value corrected for zero-point energy. The structure of the successive hydrates up to n = 4 are studied in an appropriate smaller basis and provide an explanation for the ease of formation of HNO₂ and H₃O⁺ in the atmosphere at the tetrahydrate level.