Title: wavenumber in vacuum
Long Title: IUPAC Gold Book - wavenumber in vacuum
DOI: 10.1351/goldbook.08302
Status: current

Definition
Reciprocal of the vacuum wavelength of electromagnetic radiation. \(\tilde{\nu} = 1/\lambda_{0}\).

Notes
1) Wavenumber is related to the energy change, \(\Delta E\), induced when the radiation is absorbed by \(\Delta E = hc_{0}\tilde{\nu}\), where \(h\) is the Planck constant and \(c_{0}\) the speed of the radiation.
2) Wavenumber should only be used when no confusion with frequency is possible.
3) The symbol \(\nu\) is often used instead of \(\tilde{\nu}\); this usage should be discouraged.
4) SI unit: \(\pu{m-1}\). Common unit: \(\pu{cm-1}\).

Related Terms
- electromagnetic radiation: https://goldbook.iupac.org//terms/view/08242
- vacuum wavelength: https://goldbook.iupac.org//terms/view/08300

Source
- PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 678 (https://doi.org/10.1515/pac-2019-0203)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/08302/html
- json: https://goldbook.iupac.org/terms/view/08302/json
- xml: https://goldbook.iupac.org/terms/view/08302/xml

Citation: Citation: 'wavenumber in vacuum' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08302
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Accessed: 2026-04-17T18:05:31+00:00