Solvation of the Cl-•H2O complex in CCl4 clusters:: The effect of solvent-mediated charge redistribution on the ionic H-bond

The OH stretching bands associated with the ionic H-bond in the Cl-.H2O complex are found to dramatically shift toward higher energy upon complexation with carbon tetrachloride molecules in a size selected photofragmentation study of the Cl-.H2O-(CCl4)(n), 1 less than or equal to n less than or equal to 5, clusters. The large sequential shifts (80-100 cm(-1)/CCl4) associated with addition of the first few molecules effectively tune the OH stretch v = 1 level through a Fermi resonance with the v = 2 level of the intramolecular bending vibration. By the addition of the fifth molecule, the large red-shift displayed by the bare complex (577 cm(-1) relative to isolated water) is reduced by a factor of 2. We discuss the origin of these effects in the context of charge redistrubition from chloride to the surrounding solvent molecules.