This three-year award supports U.S.-France cooperative research in physical chemistry between Kenneth C. Janda, University of California at Irvine, and Nadine Halberstadt, University of Paris, South (Orsay). The research combines theoretical and experimental studies to determine the potential energy surface for electronically excited rare gas halogen complexes known as van der Waals molecules. The objectives are (1) to obtain a detailed interpretation of vibrational predissociation for ArCl2 molecule using a newly implemented IVR (intramolecular vibrational relaxation) theory, and (2) to extend this theory to the structure and dynamics of four-atomic clusters, such as HeCl2. The U.S. research group produces very detailed spectra of van der Waals molecules for which theory is applicable. This work has yielded fundamental data about the dynamics of chemical reactions and the physical transition from gaseous to liquid state. This is complemented by the French investigator's work on scattering theory as applied to the dissociation dynamics of van der Waals molecules. The proposed effort will advance fundamental understanding of cluster dynamics and transitions from gas to liquid state.