infrared spectroscopy

https://doi.org/10.1351/goldbook.08618
Measurement principle of vibrational spectroscopy using infrared radiation.
Note:
Without qualification, 'infrared spectroscopy' usually refers to use of the mid-infrared (wavelength range 2.5 to 25 μm, wavenumber range (4000 cm−1 to 400 cm−1) region of the electromagnetic spectrum (see table).
Table 1 Regions of the electromagnetic spectrum
Spectral regionApproximate wavelength (wavenumber) rangeEnergy transitions studied in matterAnalytical techniques (spectroscopy)
Gamma1-100 pmNuclear transitions and disintegrationsGamma-ray
X-ray6 pm–100 nmIonization by inner electron removalX-ray; X-ray fluorescence
Vacuum ultraviolet10–200 nmIonization by outer electron removal
Ultraviolet200–400 nmExcitation of valence electronsUV-VIS
Visible400–780 nmExcitation of valence electronsUV-VIS
Near-infrared780 nm–2.5 μm (12 800–4000 cm-1)Excitation of valence electrons; molecular vibrational overtonesNear-IR
Mid-Infrared2.5–25 μm (4000–400 cm-1)Molecular vibrations: stretching and deformationsInfrared (IR) spectroscopy, Raman spectroscopy
Far-infrared25–1000 μm (400–10 cm-1)Molecular rotationsFar-IR, Terahertz spectroscopy
Microwave0.1–30 cmMolecular rotations and electron spinElectron spin resonance, microwave spectroscopy
Radiofrequency10−1–103 mMolecular rotations and nuclear spinNuclear magnetic resonance
Source:
PAC, 2021, 93, 647. (Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)) on page 750 [Terms] [Paper]
Citation: 'infrared spectroscopy' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.08618 RIS BibTex EndNote
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