Measurement principle of spectroscopy to analyse molecular properties based on vibrations (bond stretching or deformation modes) in chemical species.
Note: Typically, vibrational spectroscopy uses electromagnetic radiation lower in energy than the visible spectrum i.e.,
infrared or
near infrared (see table).
Table 1 Regions of the electromagnetic spectrum| Spectral region | Approximate wavelength (wavenumber) range | Energy transitions studied in matter | Analytical techniques (spectroscopy) |
|---|
| Gamma | 1-100 pm | Nuclear transitions and disintegrations | Gamma-ray |
| X-ray | 6 pm–100 nm | Ionization by inner electron removal | X-ray; X-ray fluorescence |
| Vacuum ultraviolet | 10–200 nm | Ionization by outer electron removal | |
| Ultraviolet | 200–400 nm | Excitation of valence electrons | UV-VIS |
| Visible | 400–780 nm | Excitation of valence electrons | UV-VIS |
| Near-infrared | 780 nm–2.5 μm (12 800–4000 cm-1) | Excitation of valence electrons; molecular vibrational overtones | Near-IR |
| Mid-Infrared | 2.5–25 μm (4000–400 cm-1) | Molecular vibrations: stretching and deformations | Infrared (IR) spectroscopy, Raman spectroscopy |
| Far-infrared | 25–1000 μm (400–10 cm-1) | Molecular rotations | Far-IR, Terahertz spectroscopy |
| Microwave | 0.1–30 cm | Molecular rotations and electron spin | Electron spin resonance, microwave spectroscopy |
| Radiofrequency | 10−1–103 m | Molecular rotations and nuclear spin | Nuclear magnetic resonance |
Source:
PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 769 (https://doi.org/10.1515/pac-2019-0203)