normal mode

of vibration
synonyms: normal mode, normal vibration, normal vibration mode
https://doi.org/10.1351/goldbook.08648
One of the 3N6 (3N5 for a linear molecule) modes of vibration that would add to give the total vibrational motion in a molecule if the interatomic potential were strictly quadratic in the displacements from equilibrium.
Note:
Normal modes of vibration is an idealized concept that has proved extremely useful in analysing spectra in vibrational spectroscopy.
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 757 [Terms] [Paper]