Effects of iodine on the relaxation dynamics of a photoexcited I(-)(H(2)O)(4) cluster.

ABSTRACT

The Born-Oppenheimer molecular dynamics are used to examine the relaxation dynamics of the charge-transfer-to-solvent (CTTS) photoexcited electron in I(-)(H2O)4. The dynamics are initiated from the C1' cluster configuration, which contains a dangling water molecule. The iodine atom is found to exert a repulsive force on the photoexcited electron at the beginning but an attractive force at later times of the simulation. This dual repulsion-and-attraction role of the iodine atom is found to be dependent on the ratio of the iodine-electron distance to the radius of gyration of the excited electron, d/r. In the region of d/r < ∼0.8, the iodine exerts an exclusion-repulsion force on the excited electron. Conversely, for values of d/r > ∼1.0, the iodine can exert an attractive force on the excited electron due to the induced dipole moment of iodine. However, at large iodine-electron distances, the iodine-electron interaction becomes very weak, and as a result, this attractive force is expected to fade away. Due to the heavy mass of the iodine atom, the evolution of the iodine-electron distance is driven by the motion of solvent molecules and not iodine itself. The dangling water molecules and the dipolar field of water molecules are also important in the solvent dynamics. The influence of temperature on the iodine effects and the experimental implications of the findings are also discussed.