The properties of entire spectra—specifically, the line positions and transition probabilities of perturbed series and of their adjoining continua as well as autoionization line profiles and related collision cross sections—have been interpreted in terms of a few parameters, such as quantum defects and oscillator-strength densities, which vary slowly with the excitation energy. By use of Seaton’s quantum-defect theory, the concept of separate configurations is replaced by the more comprehensive concept of channels. Alternative sets of channels are considered, related by a frame transformation whose construction is a main goal of the analysis of each spectrum. Concepts and procedures employed for these purposes since 1969 are summarized and restated here. Reference is made to extension of the treatment to negative ions, and to the direct ab initio calculation of the channel parameters to be compared with experimental results. Illustrative results are presented, as well as a guide to relevant literature.
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