Wavenumber (Cm⁻¹)
Definition
The number of wavelengths per centimetre, equal to 1/λ when λ is in cm. The working unit of vibrational spectroscopy because it is directly proportional to energy and avoids the inconvenient powers of ten that nanometres and hertz introduce.
- Definition
- Wavelengths per centimetre, equal to 1/wavelength in cm
- Proportional to
- Photon energy
- Field
- Vibrational spectroscopy
Common questions
Why do spectroscopists prefer wavenumber over hertz or nanometres for everyday work?+
Wavenumber values for vibrational transitions fall in a convenient range of roughly hundreds to thousands, avoiding the very large exponents of frequency in hertz and the very small fractional values of wavelength in nanometres, which makes spectra easier to read and compare at a glance.
Is wavenumber the same concept in Raman spectroscopy as in infrared spectroscopy?+
The unit is used the same way in both, but Raman spectra typically report a wavenumber shift relative to the excitation laser line rather than an absolute position, so a Raman shift value is not directly comparable to an absolute IR wavenumber without accounting for that difference.
Related terms
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