Charge-Transfer-to-Solvent-Driven Dissolution Dynamics of I-(H2O)2-5 upon Excitation: Excited-State ab Initio Molecular Dynamics Simulations
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- 作者：Maciej Koaski ; Han Myoung Lee ; Chaeho Pak ; Kwang S. Kim
- 刊名：Journal of the American Chemical Society
- 出版年：2008
- 出版时间：January 9, 2008
- 年：2008
- 卷：130
- 期：1
- 页码：103 - 112
- 全文大小：440K
- 年卷期：v.130,no.1(January 9, 2008)
- ISSN：1520-5126
文摘
In contrast to the extensive theoretical investigation of the solvation phenomena, the dissolutionphenomena have hardly been investigated theoretically. Upon the excitation of hydrated halides, whichare 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 hydratedhalides into halide radicals and electron-water clusters. Here we demonstrate the charge-transfer-to-solvent(CTTS)-driven femtosecond-scale dissolution dynamics for I-(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 I-(H2O)n=2-5, a simplepopulation decay is observed for small clusters (2 n 4), while rearrangement to stabilize the excesselectron to an entropy-driven structure is seen for n = 5. These results are in excellent agreement with theprevious ultrafast pump-probe experiments. For the first ~30 fs of the simulations, the iodine plays animportant role in rearranging the hydrogen orientations (although the water network hardly changes), whichincreases the kinetic energy of the cluster. However, ~50 fs after the excitation, the role of the iodineradical is no longer significant. After ~100 fs, the iodine radical is released, and the solvent moleculesrearrange themselves to a lower free energy structure. The CTTS-driven dissolution dynamics could beuseful in designing the receptors which are able to bind and release ions in host-guest chemistry.