Mimicking solvent shells in the gas phase.: II.: Solvation of K+ -: art. no. 024319

The observed gas-phase coordination number of K+ in K+(H2O)(m) clusters is smaller than that observed in bulk solution, where the coordination number has been reported to be between 6 and 8. Both theoretical and gas-phase studies of K+(H2O)(m) cluster ions point to a coordination number closer to 4. In the gas phase, the coordination number is determined by a variety of factors-the most critical being the magnitude of the K+center dot ligand pairwise interaction. Decreasing the magnitude of the ion center dot ligand interaction allows more ligands to directly interact with the cation. One method for decreasing the ion center dot ligand interaction in K+(H2O)(m) clusters is to systematically substitute weakly bound ligands for the more strongly bound water molecules. The systematic introduction of para-difluorobenzene (DFB) to K+(H2O)(m) clusters was monitored using infrared photodissociation spectroscopy in the OH stretching region. By varying the ratio of DFB molecules to water molecules present in K+(H2O)(m)(DFB)(n) clusters, the observed coordination number of gas-phase K+ was increased to 8, similar to that reported for bulk solution. (c) 2006 American Institute of Physics.