Charge-transfer-to-solvent-driven dissolution dynamics of I-(H2O)2-5 upon excitation:: Excited-state ab initio molecular dynamics Simulations

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 femitosecond-scale dissolution dynamics for I-(H2O)(n=2-5) clusters using excited state (ES) ab initio molecular dynamics (AlMD) 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 simple population decay is observed for small clusters (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 similar to 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, similar to 50 fs after the excitation, the role of the iodine radical is no longer significant. After similar to 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.