Theoretical investigations on the nature of interactions in ions (Li+, Na+, Be2+, Mg2+)-water clusters in the gas phase

The nature of interaction that is present in ion-water (M(H2O)nM(H2O)n) (M= Li+M= Li+, Na+Na+, Be2+Be2+, Mg2+Mg2+) (n = 1-10) clusters are highlighted in the present work. We have used theories of atoms in molecules, symmetry-adapted perturbation, and infrared spectroscopy in the gas phase. The inner structure where the M is surrounded by four H2OH2O molecules represent the first shell, followed by the second shell, which is the most stable cluster when n >= 4n >= 4, for M(H2O)nM(H2O)n (M= Li+M= Li+, Na+Na+, Be2+Be2+) clusters, and n >= 6n >= 6 for M(H2O)nM(H2O)n (M=Mg2+M=Mg2+) cluster. The successive binding energies of M(H2O)nM(H2O)n clusters leads to the conclusion that the affinity for water molecules follows the trend: Be2+>Mg2+>Li+>Na+Be2+>Mg2+>Li+>Na+. The SAPT study demonstrates that the total interaction energy of Be2+-waterBe(2+)-waterclusters are higher than the other clusters because of high attractive induction and electrostatic energy. The IR spectrum results conclude that in the presence of cations in (H2O)n(H2O)n clusters blue shifts occur for the hydrogen-bonded O-HO-H stretching mode, and a red shift occurs for the free O-HO-H stretching mode. This investigation contributes significantly to the scientific understanding of these clusters' bonding interactions, total interaction energy, and successive interaction energy.