Proposed modification of the criterion for the region of validity of the inverse-power expansion in diatomic long-range potentials

A modified internuclear distance criterion, RLR-m, as the lower bound for the region of validity of the inverse-power expansion of the diatomic long-range potential is proposed. This new criterion takes into account the spatial orientation of the atomic orbitals while retaining the simplicity of the traditional Le Roy radius, RLR for the interaction of S state atoms. Recent experimental and theoretical results for various excited states in Na2 suggest that this proposed RLR-m is an appropriate generalization of RLR.