1. Handb;Salpeter E. E.;Pliys.,1957
2. Dirac P . A. M. 1958 The principles oj quantum mechanics 4th ed. p. 257. Oxford U niversity Press.
3. Griffith J . S. 1961 The theory of transition metal ions p. 122. Cambridge U niversity Press.
4. M ol;Longuet H .;Phys.,1962
5. A Modified Perturbation Procedure for a Problem in Paramagnetism