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2. J. R. Streitweiser, Molecular Orbital Theory for Organic Chemists, John Wiley and Sons, London (1962).
3. G. M. Barrow, Introduction to Molecular Spectroscopy, Mc Graw-Hill, New York (1962).
4. C. J. Ballhausen, Introduction to Ligand Field Theory, Mc Graw-Hill, New York (1962).
5. H. H. Jaffe and M. Orchin, Theory and Applications of Ultraviolet Spectroscopy, John Wiley and Sons, New York (1964).