Characterization of the bond between hydrogen and the non-nuclear attractor in anionic water clusters.

The bonding interaction between non-hydrogen-bonded (NHB) hydrogen atoms and the non-nuclear attractor (NNA) observed in cavity-bound anionic water clusters has been investigated using ab initio methods. The clusters range in size from four to ten water molecules and generally consist of several water molecules hydrogen-bonded in a ring, with two of these rings stacked such that the NHB hydrogen atoms are directed towards a central cavity. Analysis of the electron density using the theory of atoms in molecules yields information about the bonding interaction that cannot be obtained with conventional computational techniques. The results indicate that this novel interaction, Ha...NNA, is a weak, closed-shell interaction. Further analysis of the atomic properties of the NHB hydrogen atoms indicate that this novel bond cannot be classified as a hydrogen bond. On the basis of the results from the current investigation, this interaction is best described as a weak dipole-ion interaction between the positively charged NHB hydrogen atoms and the negatively charged NNA.