Coupling of vibrational displacements through terms in the
vibrational potential energy. The second-order (quadratic) terms cause harmonic potential coupling while the cubic and higher terms cause anharmonic potential coupling.
See also: anharmonicity, harmonicity
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 760 (https://doi.org/10.1515/pac-2019-0203)