The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher energy near-IR, approximately 14000–4000 cm−1 (0.8–2.5 μm wavelength) can excite overtone or harmonic vibrations. The mid-infrared, approximately 4000–400 cm−1 (2.5–25 μm) may be used to study the fundamental vibrations and associated rotational-vibrational structure. The far-infrared, approximately 400–10 cm−1 (25–1000 μm), lying adjacent to the microwave region, has low energy and may be used for rotational spectroscopy. The names and classifications of these subregions are conventions, and are only loosely based on the relative molecular or electromagnetic properties.
Fourier-Transform Infrared Spectroscopy
Fourier-Transform Infrared spectroscopy (FT-IR) is a well-established and proven analytical technique for the identification of unknown chemicals. The method relies on the microscopic interaction of infrared light with chemical matter via a process of absorption and results in a pattern of bands called a spectrum. This spectrum is unique to the chemical and acts like a “molecular fingerprint” in the same way a human’s fingerprint is distinct.
FT-IR exploits the intrinsic properties of a chemical, in addition to being broadly-applicable. These features make FT-IR very amenable to spectral library-matching. With the help of an extensive database, the library-matching approach makes it possible to identify rapidly thousands of chemicals based on their distinct “molecular fingerprint”.
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