Theoretical studies on hydrogen bonding in hydroxylamine clusters and liquid

Structures and interaction energies of dimers and trimers of hydroxylamine (NH2OH) were investigated using an intermolecular potential derived from the test-particle model (T-model). The T-model results were examined using ab initio calculations at various levels of accuracy, ranging from MP2/6-311G(d,p) to MP2/6-311+ +G(2d,2p) for the dimers, as well as from MP2/6-31G(d,p) to MP2/6-311++G(2d,2p) for the trimers. Both T-model and MP2 calculations confirmed that a cyclic arrangement of O-H ... N hydrogen bonds (H-bonds) represents the absolute minimum energy geometry of the dimers. Several local minimum energy geometries were suggested based on the T-model and MP2 results. For the trimers, the T-model and MP2 predicted a slightly different absolute minimum energy geometry. The T-model preferred a compact H-bonded structure, whereas MP2 with the largest basis set preferred a stacked H-bond arrangement. Ab initio calculations at the SCF/6-311+ +G(2d,2p) level showed that the effects of electron correlation play an important role in the association of compact H-bonded clusters. Some properties of liquid NH2OH were investigated based on the T-model potential. Molecular Dynamics (MD) simulations were performed for the liquid at 318 and 329 K. MD results suggested a slightly higher possibility of finding the O-H ... O H-bond, compared to the O-H ... N H-bond in the liquid. There was no direct evidence showing the existence of cyclic dimers in the liquid. (C) 1999 Elsevier Science B.V. All rights reserved.