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Width of an infrared absorption band

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  424

2026-11-11

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Width of an infrared absorption band

In ultraviolet (UV) and visible electronic absorption spectroscopy, absorption is limited to the excitation of a single electron in a chromophore, albeit to one of several excited states. An electronic spectrum is rarely composed of more than three prominent spectral features. However, the energy required to excite an electron is enough also to excite associated vibrational and rotational states, and the absorption profile is broad.

The UV–visible spectrum is characterised by only a few broad features. A typical half-height width of a UV–visible absorption is between 2000 and 5000 cm^-1.

The IR spectrometer sees the excitation of bond vibrations and associated rotational motions. In contrast to UV-visible, the IR spec trum comprises many relatively sharp features that provide an excellent fingerprint for identification. A typical half-height width of an IR absorption band is 10–20 cm1. The UV and IR spectra for hydrocortisone are shown in Figure 1, illustrating the broad spectral features of the UV spectrum relative to the information-rich IR spectrum with its far sharper features. Note that the region above 2000 cm1 is not shown in Fig. 1B.

Figure 1 (A) UV spectrum and (B) IR spectrum of hydrocortisone.