Rare gas-dihalogen potential energy surfaces

Even though the rare gas-halogen interactions have been among the most intensively studied intermolecular forces, it is only in the last few years that qualitatively correct potential energy surfaces have become available for the ground electronic states. Previously, spherical atom-atom potentials were commonly used, and these potentials could not account for the linear minima of the true surface. The two dimensional potentials for HeClF and for example, are now known rather precisely except for regions far from the potential NeCl2, minima. The third dimension of these potentials, the dependence of the interaction with the rare gas atom as a function of the halogen bond length, still remains to be completely investigated. For even the qualitative 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 states of the halogens have also been intensively studied. For these states, the spherical atom-atom potentials are much more accurate and produce agreement with much of the experimental data. However, the non-spherical terms in the potential and the effects of electronic non-adiabaticity are only now being quantitatively studied. For most other electronic states, very little quantitative work has been performed. This review gives a historical overview of this work, summarizes the current state of our understanding, and proposes avenues for further investigation.