The Quantum-Mechanical Treatment of Rotational and Vibrational Spectra
Taking the diatomic molecule as an example, we introduce the Born-Oppenheimer approximation, which then permits the approximate separation of the molecular wavefunctions into electronic and nuclear parts. The rotational and vibrational motions are described by the nuclear wavefunction. We then consider the rotation of tri- and polyatomic molecules, giving a detailed discussion of both the symmetric and the asymmetric tops. In the treatment of molecular vibrations, the concept of normal coordinates plays an important role; here, again, symmetry considerations prove to be very useful, and we discuss them in the final sections of this chapter.
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