1. C.E. Moore, ‘Atomic Energy Levels’, National Bureau of Standards Circular 467 (1952).
2. J. Ferguson, ‘Progress in Inorganic Chemistry’, edited by S.J. Lippard, 12, 159 (1970).
3. For a simple description of the propagation of light in biaxial crystals, see C. Bunn, ‘Crystals: Their Role in Nature and Science’, Academic Press, N.Y. (1964).
4. J.S. Griffith, ‘The Theory of Transition-Metal Ions’, Cambridge University Press (1961).
5. C.J. Ballhausen, ‘Introduction to Ligand Field Theory’, McGraw-Hill, New York (1961).