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Chapter 13 Infrared Spectroscopy Tutorial
In this figure, note the following:
Source of IR radiation - Heated wire in the SapphIRe Analyzer
Sample Cell – 0.5 or 12.5 m pathlength cell in the SapphIRe Analyzer
Optical Filter - permits selection of a single, specific wavelength of IR radiation
to reach the detector
Detector - The pyroelectric, heat-sensitive element used to measure IR energy
emerging from the sample cell
In a typical infrared spectrophotometer, a source simultaneously emits all the infrared
wavelengths. These wavelengths cover nearly all the natural vibrational frequencies of
organic compounds. One of the natural vibrational frequencies of the Tetrahydrofuran
(THF) molecule, for example, occurs at about 1064 cm
infrared frequencies are beamed through a sample of THF in the sample cell, some of the
radiation at the wavenumber 1064 are absorbed by the THF molecules, whereas most of
the other frequencies are transmitted. This absorption can be plotted using a common
strip chart recorder to produce an air-referenced spectrum similar to that in (Figure 13-8).
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Infrared spectra are specific for the compound analyzed. Like fingerprints, no two are the
same. This provides a means for identifying an organic substance.
A typical spectrum is a plot of absorption (or transmission) of infrared energy (radiation)
against its wavelength (λ) or wavenumber (ν). As indicated in Figure 13-7, the drive of
the optical filter is synchronized with the x-axis of the chart recorder so that the latter
indicates the wavelength of radiation reaching the detector via the slit. It is important to
note that the SapphIRe Analyzer operates continuous wavelengths from 7.7 to 14.1
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Wavelength In Microns
Figure 13-8. Scan of Tetrahydrofuran (THF)
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(9.40 microns). If all the
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