1. Ballhausen, C.J.: Introduction to Ligand Field Theory, New York: McGraw-Hill 1962
2. J�rgensen, C.K.: Absorption Spectra and Chemical Bonding in Complexes, London: Pergamon 1962
3. J�rgensen, C.K.: Modern Aspects of Ligand Field Theory, Amsterdam: North-Holland 1971
4. van Vleck, J.H.: J. Chem. Phys.3, 807 (1935)
5. Ros�n, A., Ellis, D.E.: Chem. Phys. Lett.27, 595 (1974); J. Chem. Phys.62, 3039 (1975)