local mode

of vibration
synonym: local mode
https://doi.org/10.1351/goldbook.08633
Mode of vibration localized in one type of bond.
Note:
For highly excited \(\ce{CH}\) stretching vibrations anharmonic interactions mix the normal modes of vibration to the point that each observed mode of vibration behaves as a local mode.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 753 (https://doi.org/10.1515/pac-2019-0203)