The dynamics of noble gas--halogen molecules and clusters

The vibrational relaxation of noble gas-halogen van der Waals clusters has been fertile territory for the development of experimental and theoretical tools for state-to-state dynamics studies. Proceeding through the various combinations of noble gas atoms and halogen molecules, one goes from "simple" direct vibrational predissociation, through sequential relaxation pathways, to the statistical intramolecular vibrational relaxation limit. In some cases the vibrational processes dominate, in others electronically nonadiabatic processes, including chemical reactions, interfere. Thus the noble gas-halogen species provide test cases for most of the dynamical processes available to more "normal" molecules. This review discusses the current state-of-the-art for such studies and points to important problems that remain to be solved.