Model analysis of bonding in the alkali halide molecules

Bonding in the complete series of the alkali halide molecules is analyzed in the framework of a semiempirical covalent model, based on exchange-perturbation theory of the Rayleigh-Schrodinger type and on a minimal basis set of ''optimized'' gaussian orbitals. Results are compared with those of an ionic model which is a simple extension of Unsold's original treatment of the hydrogen molecular ion. The two methods yield equivalent results, with an accuracy in the spectroscopic constants comparable to that of the best existing ab initio calculations; the accuracy improves with increasing size of the atoms.