Direct dynamics simulations of photoexcited charge-transfer-to-solvent states of the I−(H2O)n (n = 4, 5 and 6) clusters

The dynamics of photoexcited charge-transfer-to-solvent (CTTS) states of the I−(H2O)n (n = 4, 5 and 6) clusters has been studied using the on-the-fly direct dynamics technique in order to understand recent femtosecond pump-probe experiments from a theoretical viewpoint. The lowest triplet potential energy surface at the hybrid B3LYP density-functional electronic structure level was employed to model the CTTS singlet excited-state potential energy surface due to small singlet-triplet splittings. A total of 13 structures of the I−(H2O)n cluster were vertically excited with the initial kinetic energy being zero and subsequent trajectory simulations were performed up to 1.5-2.0 ps. It was found that features of time-evolution of vertical detachment energy of an excess electron and dipole moment along the trajectory is strongly dependent of the initial cluster structure employed. The simulations revealed that the structural change in the water network configuration due to breaking of hydrogen-bonds plays an important role in the dynamics. I-atom detachment from the cluster was not observed during simulation time but this result is presumably due to the too strong attractive interaction between I and H2O on the B3LYP potential energy surface.