Ar•••I2:: A model system for complex dynamics

We review spectroscopic and photodissociation dynamical studies in the region of the B <-- X transition of the Ar (...) I-2 van der Waals complex, both below and above the dissociation limit of the B ((3)Pi 0(u)(+)) state. This very simple system constitutes a prototype for a wide range of molecular processes: vibrational predissociation involving intramolecular vibrational relaxation, electronic predissociation, cage effect..... Each of these processes has been or still is the subject of differing interpretations: intramolecular vibrational relaxation involved in the vibrational predissociation of this system can be in the sparse or statistical regime, vibrational and electronic predissociation are in competition and a direct, ballistic interpretation of the cage effect as well as a non-adiabatic one have been proposed. The study of the dependence of these dynamical processes on the relative orientation of the two partners of the complex (stereodynamics) is made possible by the coexistence of two stable Ar I-...(2)(X) isomers. Experimental as well as theoretical results are reviewed. Experiments range from frequency-resolved to time-dependent studies, including the determination of final state distributions. Theoretical studies involve potential energy surface calculations for several electronic states of the complex and their couplings and adiabatic as well as non-adiabatic dynamical simulations.