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3. The Nature of the Chemical Bond. Ithaca: Cornell Univ. Press 1960.
4. Eyring, H., J. WALTER and G. E. Kimball: Quantum Chemistry. New York: Wiley 1944.
5. Herzberg, G.: Molecular Spectra and Molecular Structure. I. Spectra of Diatomic Molecules. New York: D. Van Nostrand Co. 1950.