Cubic anharmonic resonance (see
anharmonicity), i.e., any interaction caused by cubic terms in the
vibrational potential energy.
Notes: - Traditionally, Fermi resonance was defined as the anharmonic interaction between a fundamental state and one or more overtone or combination transitions.
- Fermi resonance is usually identified by the presence of more than one band of comparable intensity when only one fundamental is expected. Also seen as an Evans hole.
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 746 (https://doi.org/10.1515/pac-2019-0203)