Rydberg-like properties of rotational–vibrational levels and dissociation continuum associated with alkali–halide charge–transfer states

Fully quantal calculations for the vibrational bound levels and adjoining continuum of alkali–halide charge–transfer states have been made using new algorithms derived from the Milne quantum number function for the radial motion of the diatom. Because of the asymptotic Coulombic interaction, the molecular potential actually supports an infinite number of bound vibrational states which conform to a Rydberg-like spectrum and can be characterized by a vibrational quantum defect. As predicted by conventional quantum defect theory for perturbed Rydberg series, we also observe that the vibrational quantum defect extrapolates across the dissociation limit to yield the threshold elastic scattering phase shift for the dissociative continuum state. The implicit dependence of the defect on the rotational state of the molecule yields a complete description of the rotational–vibrational spectrum. Because the system is heavy, the mass and rotational dependence of the computed quantum defects generally conform to appropriate WKB-like predictions. The usefulness of our numerical results in forthcoming investigations of two body collisional charge–transfer processes is also indicated.