vibrational spectrum

A vibrational spectrum is a part of a molecular spectrum where bands originate from quantized changes in the energy of atomic vibrations within a molecule. This phenomenon is studied using techniques like infrared spectroscopy, which analyzes the absorption of infrared radiation due to molecular vibrations.12

In infrared spectroscopy, molecules absorb specific frequencies of light that correspond to their natural vibrational modes. For a diatomic molecule, there's one primary vibration: bond stretching. Polyatomic molecules have more complex vibrations, with the number of possible modes depending on the number of atoms. The energy of these vibrations is quantized, meaning molecules can only exist in specific vibrational energy states, described by a vibrational quantum number.23

Raman spectroscopy offers complementary information by observing how molecules scatter light. When photons interact with a molecule, they can gain or lose energy, resulting in scattered light at different frequencies that correspond to the molecule's vibrational and rotational transitions. This allows for the observation of vibrational transitions that might not be apparent in infrared spectra, especially for highly symmetrical molecules.4