Wavenumber
Definition
The reciprocal of wavelength expressed in cm-1, the universal IR axis. Higher wavenumber means higher photon energy. The mid-IR window is 4000 to 400 cm-1.
- Definition
- Reciprocal of wavelength, in cm-1
- Relation to energy
- Higher wavenumber means higher photon energy
- Mid-IR range
- 4000 to 400 cm-1
Common questions
Why does infrared spectroscopy use wavenumber instead of wavelength or frequency?+
Wavenumber is directly proportional to photon energy and produces evenly spaced, easy-to-read peak positions across a spectrum, avoiding the very small decimal values of wavelength in micrometres or the unwieldy large numbers of frequency in hertz that would otherwise clutter an FTIR plot.
How does a wavenumber value help identify a functional group in FTIR analysis?+
Specific molecular bonds vibrate at characteristic wavenumbers, such as carbonyl stretches appearing near 1700 cm-1, so matching an unknown sample's absorption peaks against known functional-group ranges lets an examiner infer the chemical structure of the material being tested.
Related terms
- ATR-FTIR
- Attenuated Total Reflectance Fourier-Transform Infrared Spectroscopy: a non-destructive mid-infrared method that analyses a single drop of milk pressed against an ATR crystal....
- Fingerprint Region
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- FTIR
- Fourier-transform infrared spectroscopy. A Michelson interferometer modulates all wavelengths simultaneously, the interferogram is Fourier-transformed into the conventional absorbance versus wavenumber spectrum.
- Group Frequency
- A characteristic absorption band associated with a specific functional group (carbonyl about 1700 cm-1, hydroxyl 3200 to 3600 cm-1) used to read...
- KBr Pellet
- A classical solid sample mode: 1 to 2 mg analyte ground with about 200 mg dry KBr and pressed in a 13...