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microns. The signal from the detector is transmitted to the y-axis of the recorder,
indicating how much radiation is absorbed by the sample at a particular wavelength.
Thus, any point on the curve of an absorption spectrum can characterized by two factors:
wavelength and the intensity of IR energy absorption.
Absorption Peaks
The wavelength at which maximum energy absorption occurs is called an absorption
peak. It is a narrow band of frequencies of energy strongly absorbed by compounds in a
sample cell. The absorption peak's wavelength value is a qualitative measurement. While
frequency or wavenumber is often used to indicate this information, wavelength in μ m
units is also used to identify absorption peaks.
Note: Viewing absorption peak values on spectral charts gives only a rough
approximation of the specific values of absorption peaks. Much greater accuracy can be
achieved with computer-aided analyzers such as the SapphIRe Analyzer.
If the sample cell were completely clean of any absorbing gases (including air), the
absorption spectrum would look like that shown in Figure 13-9).
0.020
0.015
0.010
0.005
0.000
8
-0.005
Chapter 13 Infrared Spectroscopy Tutorial
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10
Wavelength In Microns
Figure 13-9. Blank Air Reference Scan
13-9
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