Ab initio molecular orbital treatment of hydroxylamine-X +-water and hydroxylamine-X +-ammonia (X = H, Li) clusters

Abstract

The structure and energetics of hydroxylamine-X +-H 2O and hydroxylamine-X +-NH 3 (X = H, Li) clusters have been examined by ab initio molecular orbital methods including the effects of electron correlation by Møller-Plesset perturbation theory. Solvation by one molecule of water leads to a considerable change in the structure of protonated hydroxylamine, which is clearly shown by the topological characteristics of the Laplacian of the electronic charge distribution. Solvation by one molecule of ammonia is generally accompanied by a proton transfer from the base to the solvent molecule. A detailed analysis of this proton transfer process is offered. For protonated species there is not a clearly privileged site for solvation, but solvation energies of oxygen protonated species are systematically higher than those of nitrogen protonated ones. Consequently, the gap between gas-phase nitrogen and oxygen proton affinities decreases considerably upon solvation by one molecule of water and practically disappears upon solvation by one molecule of ammonia. Solvation of hydroxylamine-Li + complexes takes place preferentially on the Li + ion, but in this case there are no significant differences between hydration or ammoniation energies of oxygen-Li + versus nitrogen-Li + complexes. BSSE and ZPE contributions to the clustering energies are not negligible. MP2 correlation energy contributions are always positive, i.e., lead to a stabilization of all clusters and they account for 10 to 25% of the total stabilization energy.