This research, part of the Experimental Physical Chemistry Program, is designed to develop and use new techniques for the study of size-selected ionic clusters. Insight will be obtained on the structure and dynamics of various clusters, the relationship to properties of the condensed phase, and the nature of ion-solvent interactions. Professor Okumura's research is supported by a Presidential Young Investigator (PYI) Award. The experiments will be accomplished on a sophisticated ion beam apparatus designed for infrared and optical spectroscopy of mass-selected ions. High efficiency ion counting techniques will be used to detect indirectly the absorption of laser radiation through tandem mass spectrometry. Time-resolved pump-probe experiments will be used to explore the dynamics of reactive processes within simple and complex (including solvated) clusters and in the condensed phase. Mass-selected clusters will also be deposited on appropriate substrates for structural probing at atomic resolution using scanning tunneling microscopy.