Spectral and electron-collision properties of atomic ions: Threshold phase shifts

Threshold phase shifts (or equivalently, quantum defects at the series limit) are calculated within the framework of the Hartree-Slater (central-field) approximation for positive atomic ions with nuclear charge number Z{≤}37. The results are displayed in isoelectronic (the number of electrons, N, constant), isonuclear (Z constant), and isoionic (Z-N constant) pictures. The systematics of the threshold phase shifts are delineated, and the utility of each of the pictures is discussed. The possibilities and pitfalls of interpolation to generate new data are also discussed. This paper represents the initial report of a systematic investigation of ionic properties.