Matter, interaction with infrared

Not all matter is capable of producing an infrared spectrum (e.g., metals do not). To interact with infrared radiation the molecule must have a permanent dipole moment and must vibrate about a bond (changing the bond length or angle), or rotate about an axis perpendicular to the bond. It is the interaction of radiation with these vibrations and rotations that gives rise to the absorption bands appearing on the spectrogram. 

The vibrational motions of the chemically bound constituents of matter have fre-quencies in the infrared regime. The oscillations induced by certain vibrational modes provide a means for matter to couple with an impinging beam of infrared electromagnetic radiation and to exchange energy with it when the frequencies are in resonance. In the infrared experiment, the intensity of a beam of infrared radiation is measured before (Iq) and after (7) it interacts with the sample as a function of light frequency, w[. A plot of I/Iq versus frequency is the infrared spectrum. The identities, surrounding environments, and concentrations of the chemical bonds that are present can be determined. 

When dealing with low-energy infrared radiation, the interaction with matter is limited to the absorption of light by the outer shell electrons, i.e. those used in forming compounds. Hence, particular bonds will absorb particular wavelengths. This is the principle used for infrared spectroscopy. There are equivalent techniques for ultraviolet radiation and visible radiation, but they are mostly used to provide information about concentration of a given compound, rather than for identification purposes such as XRF or IR techniques. 

We can understand the interactions of infrared radiation with matter in terms of changes in the molecular dipoles associated with vibrations and. rotations. We will not go into great depth about the classical and quantum theories of infrared spectroscopy— such detail is really beyond The scope of this present book. Those interested in gaining more in-depth knowledge of the background theory will find that most standard, Physical Chemistry texts provide a detailed coverage of this topic. 

Light, which is a form of electromagnetic radiation, can interact with matter in a number of different ways. The interaction of light of a given wavelength with a particular object depends on the molecular structure of the objeet. Ineident light may be transmitted, refleeted, absorbed, or scattered by the molecules. Infrared (IR) speetroseopy is a particular type of absorption spectroscopy whereas Raman speetroseopy arises via the inelastie scattering of photons by molecules of the object. Both the strueture and the eleetronie distribution of the molecule determine the intensity of a vibrational transition for eaeh teehnique. In this sense, the methods may be considered to be complementary, and in some eases a eombination of both may prove to be especially useful [14,15]. 

Thus, infrared spectroscopy is the study of the interaction of matter with hght radiation when waves travel through the medium (matter). The waves are electromagnetic in nature and interact with the polarity of the chemical bonds of the molecules [3]. If there is no... 

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