Wavenumber (Cm^-1)
Definition
Reciprocal of wavelength in centimetres, the standard unit for mid-infrared spectra; 1 cm^-1 = 10^7 / λ(nm).
- Unit
- cm^-1
- Conversion
- 1 cm^-1 = 10^7 / wavelength in nm
- Application
- Standard unit for mid-infrared spectra
Common questions
Why is the nanometre-to-wavenumber conversion useful to a forensic analyst reading spectra?+
Instrument software and reference libraries sometimes report peak positions in different units, so being able to convert between nanometres and cm^-1 lets an analyst cross-check a spectral feature against a reference database that uses a different convention without misreading the peak location.
Does a higher wavenumber always mean a stronger absorption?+
No. Wavenumber only indicates where on the energy scale a vibration occurs, not how strongly the sample absorbs at that position; peak height or area, which depends on concentration and the bond's dipole change, is what indicates absorption strength.
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