Quantum chemical study of the interaction of nitrate anion with water

The interaction between nitrate anion and water has been investigated by Hartree-Fock calculations with the 6-311 + G(d,p) basis set and by B3LYP density functional calculations with the aug-cc-pVTZ basis set, it is found that the global energy minimum is a planar configuration where both hydrogen atoms of water are coordinated to two oxygen atoms of NO3- by distorted hydrogen bonds. in contrast to former studies on NO3- /H2O this configuration is found to be asymmetric at the highest theoretical level employed. The corresponding structure with C-2 nu symmetry is a saddle point at slightly higher energy. A singly hydrogen-bonded configuration is still about 2.4 kcal/mol higher in energy. The shifts in the vibrational frequencies of water and nitrate upon complexation were calculated. A compact analytical potential function of NO3-/H2O for use in statistical thermodynamic simulations was obtained from 390 points of the energy surface and an intramolecular force field for the nitrate anion is presented. (C) 1998 John Wiley & Sons, Inc.