* E. U. Condon and G. H. Shortley, "The Theory of Atomic Spectra", (1970) Cambridge at the University Press, ISBN 0-521-09209-4, "See chapter 3".
* E. U. Condon and G. H. Shortley, "The Theory of Atomic Spectra", (1970) Cambridge at the University Press, ISBN 0-521-09209-4, "See chapter 3".