Rare gas-dihalogen potential energy surfaces

Even though the rare gas-halogen interactions have been among the most inte nsively studied intermolecular forces, it is only in the last few years tha t qualitatively correct potential energy surfaces have become available for the ground electronic states. Previously, spherical atom-atom potentials w ere commonly used, and these potentials could not account for the linear mi nima of the true surface. The two dimensional potentials for HeClF and for example, are now known rather precisely except for regions far from the pot ential NeCl2, minima. The third dimension of these potentials, the dependen ce of the interaction with the rare gas atom as a function of the halogen b ond length, still remains to be completely investigated. For even the quali tative ArI2, aspects of the surface are still in considerable dispute. The interactions of the rare gas atoms with the B (3)Pi(0) excited electronic s tates of the halogens have also been intensively studied. For these states, the spherical atom-atom potentials are much more accurate and produce agre ement with much of the experimental data. However, the non-spherical terms in the potential and the effects of electronic non-adiabaticity are only no w being quantitatively studied. For most other electronic states, very litt le quantitative work has been performed. This review gives a historical ove rview of this work, summarizes the current state of our understanding, and proposes avenues for further investigation.