Overtones are observed in the vibrational spectra of diatomic molecules when:a)Anharmonicity is large.b)Anharmonicity is absent.c)Vibrational and rotational modes are coupled.d)An alternating electric field is applied.Correct answer is option 'C'. Can you explain this answer?

Question

Answer

Explanation:

Introduction:
Overtones are observed in the vibrational spectra of diatomic molecules when vibrational and rotational modes are coupled.

Vibrational and rotational modes:
Vibrational modes refer to the movements of atoms within a molecule, while rotational modes refer to the rotation of the molecule as a whole. In diatomic molecules, the vibrational and rotational modes are coupled, meaning that they interact with each other.

Overtones:
Overtones are higher energy states of a molecule's vibrational mode. They are observed when a molecule absorbs energy that is greater than the energy required to excite the fundamental vibrational mode.

Explanation:
When vibrational and rotational modes are coupled, the energy levels of the molecule become more complex. The result is that the vibrational modes split into sub-levels, and overtones are observed when the molecule absorbs energy that corresponds to these sub-levels.

In contrast, if anharmonicity is absent, the molecule's vibrational modes would be simple and would not split into sub-levels. Similarly, an alternating electric field does not affect the vibrational modes of a molecule.

Therefore, the correct option is C, which states that overtones are observed in the vibrational spectra of diatomic molecules when vibrational and rotational modes are coupled.

Answer

Maybe a case of Fermi Resonance

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