NH4~+ Resides Inside the Water 20-mer Cage As Opposed to H3O~+, Which Resides on the Surface: A First Principles Molecular Dynamics Simulation Study

摘要

Experimental vibrational predissociation spectra of the magic NH4~+(H2O)_(20) clusters are close to those of the magic H3O~+(H2O)_(20) clusters. It has been assumed that the geometric features of NH4+(H2O)_(20) clusters might be close to those of H3O~+(H2O)_(20) clusters, in which H3O+ resides on the surface. Car-Parrinello molecular dynamics simulations in conjunction with density functional theory calculations are performed to generate the infrared spectra of the magic NH4~+(H2O)_(20) clusters. In comparison with the experimental vibrational predissociation spectra of NH4~+(H2O)_(20), we find that NH4~+ is inside the cage structure of NH4~+(H2O)_(20) as opposed to on the surface structure. This shows a clear distinction between the structures of NH4~+(H2O)_(20) and H3O~+(H2O)_(20) as well as between the hydration phenomena of NH4~+ and H3O~+.