ABSTRACT
Infrared (IR) radiation was rst discovered in 1800 by Sir William Herschel, who used a glass prism with blackened thermometers as detectors to measure the heating effect of sunlight within and beyond the boundaries of the visible spectrum. Coblentz laid the groundwork for IR spectroscopy with a systematic study of organic and inorganic absorption spectra. Experimental difculties were immense. Since each point in the spectrum had to be measured separately, it could take 4 hours to record the full spectrum. But from this work came the realization that each compound had its own unique IR absorption pattern and that certain functional groups absorbed at about the same wavelength even in different molecules. The IR absorption spectrum provides a “ngerprint” of a molecule with covalent bonds. This can be used to identify the molecule. Qualitative identication of organic and inorganic compounds is a primary use of IR spectroscopy. In addition, the spectrum provides a quick way to check for the presence of a given functional group such as a carbonyl group in a molecule. IR spectroscopy and spectrometry as used by analytical and organic chemists is primarily absorption spectroscopy. IR absorption can also be used to provide quantitative measurements of compounds.
