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3. R. S. Mulliken and W. B. Person, (Eds., H. Eyring, D. Henderson and W. Jost), Physical Chemistry, Vol. 3. (Academic Press, New York, 1969), chapter 10
4. J. A. Pople, W. G. Schneider and H. J. Bernstein, High Resolution Nuclear Magnetic Resonance, (McGraw-Hill, New York and London,1959), chapter 10
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