Photofragmentation of mass-selected ICI-(CO2)(n) cluster ions: Solvation effects on the structure and dynamics of the ionic chromophore

Photofragmentation studies at 644 nm and 740 nm of ICI-(CO2)(n) cluster ions (n=0-8) have been carried out in a tandem time-of-flight mass spectrometer. Photodissociation of these cluster ions at a wavelength at which bare ICl- produces only I- results in the formation of three classes of fragment ions: I-, Cl-, and ICl- based clusters. The I- based clusters correspond to the direct photoproduct in which a Cl atom has escaped the cluster ion. The ICl- and Cl- based clusters are a result of a nonadiabatic electronic transition to the ground state mediated by the solvent. The relative importance of these photofragment channels strongly depends on the cluster ion size. An ICl- caged product is first observed for ICl-(CO2)(2), increasing rapidly to a maximum at n approximate to 6 and then decreasing. This caging efficiency is dramatically different from the I-2(-)(CO2)(n) cluster ions where complete caging was observed for 16 solvent molecules. The Cl- photofragment channel increases smoothly for the cluster size range studied and becomes the dominant channel for n=8. The relative yields of the ICl- and Cl- based products reflect the extent to which solvation influences the photodissociation pathways of ICl-. (C) 1996 American Institute of Physics.