Molecular clusters: Structure and dynamics of weakly bound systems

Weakly bound atomic and molecular clusters can be viewed as finite-size ''pieces'' of the condensed phases of matter. From both the experimental and theoretical points of view, the finite size of these clusters is of great advantage in simplifying the system, permitting molecular level characterization of solvent effects on the solute spectroscopy and chemical reaction dynamics. In addition, the ability to vary the number of atoms or molecules in the cluster enables us to observe how its various structural and dynamical properties evolve with size, from those typical of isolated gas phase molecules toward the bulk limit. By far the most detailed information has been obtained for binary complexes, where the issues of interest are the determination of intermolecular potential energy surfaces and understanding the vibrational dynamics of these complexes. Considerable progress has also been made in the characterization of higher-order complexes, which provide information on many-body interactions and more realistically approximate solvated systems. Since the breadth of this field precludes a complete review, we attempt here only to give some examples that illustrate the important issues and convey some of the excitement.