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2. E. Heilbronner J. D. Dunitz ‘Reflections on Symmetry in Chemistry… and Elsewhere’ Verlag Helvetica Chimica Acta and VCH Basel and Weinheim 1993.
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4. F. Merkt M. Quack ‘Molecular Quantum Mechanics and Molecular Spectra Molecular Symmetry and Interaction of Matter with Radiation’ Vol. 1 Chap. 1;
5. S. Albert K. Keppler Albert H. Hollenstein C. Manca Tanner ‘Fundamentals of Rotation–Vibration Spectra’ M. Quack Vol. 1 Chap. 3;