Structure and dynamics of molecular ions in clusters: I-2(-) in flexible CO2

The structures and dynamics of I-2(-) molecular ions embedded in clusters of flexible solvent molecules are studied using molecular dynamics simulation. The potential model extends the work of Papanikolas et al. [J. Chem. Phys. 102, 2452 (1995)] by taking into account the low-frequency bending vibrations of the solvent molecules. Results are presented for flexible CO2 and for a hypothetical solvent in which the bending force constant of CO2 has been decreased by a factor of 5. The structure and the vibrational relaxation dynamics of I-2(-) in flexible CO2 differ only slightly from what was seen in rigid CO2. In ''hyperflexible'' CO2, however, the solute becomes strongly polarized even at its equilibrium geometry, and the cluster structures are highly asymmetric, demonstrating that the localizing solvation forces are able to overcome the delocalizing chemical bonding interactions. The pathways for vibrational relaxation are also found to be distinctly different in the flexible and hyperflexible solvent. (C) 1997 American Institute of Physics.