IONIZATION OF BASES IN WATER - STRUCTURE AND STABILITY OF THE NH4-DOT-CENTER-DOT-CENTER-DOT-OH- IONIC FORMS IN AMMONIA-WATER CLUSTERS(CENTER)

The structure and stability of the NH4+... OH- ionic forms resultant f rom the equilibrium NH3 + H2O reversible arrow NH4+ + OH- is analyzed by Hartree-Fock, second-order Moller-Plesset, and the Becke-Lee-Yang-P arr density functional. Our results show that a double ionic cluster N H4+...(H2O)(3) ... OH-, in which three molecules are located between t he NH4+ and OH- ions, is stable and lies 5-10 kcal/mol higher than var ious neutral clusters containing one ammonia and four water molecules. The process of formation of the double ionic cluster from a geometric ally similar neutral cluster is shown to be synchronic, with the two p rotons being simultaneously transferred. The MP2 and BLYP methods give a similar description of the structure and stability of these cluster s.