Abstract
Exchange perturbation theory of the Rayleigh‐Schrödinger type is applied, in first and second orders, to the problem of bonding in rare‐gas halides. The basic model is that of a four‐electron, three‐center system with one effective electron replacing the unpaired electrons of a halogen atom, and two spin‐paired electrons representing the closed shells of the rare‐gas atom. On the basis of exchange perturbation theory, the model verifies a direct parallelism between bonding in rare‐gas compounds and the phenomenon of super‐exchange in ionic solids with paramagnetic cations. It is found that the observed stability and specific geometric configuration of the xenon and krypton fluorides are readily reproduced by the model. In addition, the model explains why other dihalides cannot exist. The two principal components of the interaction energy are found to be indirect exchange between halogen atoms via the rare‐gas atoms (attractive in the stable configurations) and, in compounds with coordination higher than two, simultaneous interactions between three halogen atoms (always repulsive). The observed approximate constancy of the binding energy per bond in xenon fluorides with increasing coordination is accounted for.