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The charge-transfer-to-solvent (CTTS)-driven femtosecond-scale dissolution dynamics for [I.sup.-][([H.sub.2]O).sub.n=2-5] clusters is analyzed by using excited state (ES) ab initio molecular dynamics (AIMD) simulations. The CTTS-driven dissolution dynamics is used for designing the receptors that are able to bind and release ions in host-guest chemistry.

Density functional and ab intio calculations are employed in order to understand the base dissociation of rubidium hydroxide by water molecules. The hydrated structures, stabilities, thermodynamic quantities, dissociation energies, infrared spectra, and electronic properties of RbOH(H2O)n=0–5 are investigated. With the successive addition of water molecules to RbOH, the Rb-OH bond lengthens significantly from 2.45 Å for n=0 to 3.06 Å for n=5. It is interesting to note that four water molecules are needed for the stable dissociation of RbOH (as an almost dissociate conformation) and five water molecules are needed for the complete dissociation without any Rb-OH stretch mode, in contrast to the same group base of CsOH which requires only three water molecules for an almost dissociate conformation and four water molecules for the complete dissociation. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Water photoexcitation and ionization process are used for studying the water photolysis. Both photoexcited and photoionized mechanisms are elucidated by using excited-state ab initio molecular dynamics simulations based on complete active space self-consistent field approach and unresistricted Moller-Plesset second-order perturbation theory based Born-Oppenheimer molecular dynamics simulations.

The theoretical studies yield several insights into the interactions prevailing in aqueous clusters of monovalent alkali metal, ammonium, and hydronium cations. The second order Moller-Plesset (MPs) and density functional levels of theory are used for the calculations of the structures, thermodynamic energies and IR spectra of several plausible conformers.

In contrast to the extensive theoretical investigation of the solvation phenomena, the dissolution phenomena have hardly been investigated theoretically. Upon the excitation of hydrated halides, which are important substances in atmospheric chemistry, an excess electron transfers from the anionic precursor (halide anion) to the solvent and is stabilized by the water cluster. This results in the dissociation of hydrated halides into halide radicals and electron-water clusters. Here we demonstrate the charge-transfer-to-solvent (CTTS)-driven femtosecond-scale dissolution dynamics for l(H2O)n=2–5 clusters using excited state (ES) ab initio molecular dynamics (AIMD) simulations employing the complete-active-space self-consistent-field (CASSCF) method. This study shows that after the iodine radical is released from 1(H2O)n=2–5, a simple population decay is observed for smallclusters (2 ≤ n ≤ 4), while rearrangement to stabilize the excess electron to an entropy-driven structure is seen for n = 5. These results are in excellent agreement with the previous ultrafast pump-probe experiments. For the first ∼30 fs of the simulations, the iodine plays an important role in rearranging the hydrogen orientations (although the water network hardly changes), which increases the kinetic energy of the cluster. However, ∼50 fs after the excitation, the role of the iodine radical is no longer significant. After ∼100 fs, the iodine radical is released, and the solvent molecules rearrange themselves to a lower free energy structure. The CTTS-driven dissolution dynamics could be useful in designing the receptors which are able to bind and release ions in host-guest chemistry. [ABSTRACT FROM AUTHOR]