INFRARED SPECTRA OF INORGANIC COMPOUNDS

This chapter discusses the experimental, theoretical, and empirical correlations between functional organic groups and the infrared spectrum. The application of infrared spectroscopy to the identification of inorganic compounds is less successful. In obtaining infrared spectra of inorganic solids, an experimental complication arises from possible chemical reaction between the inorganic compound and the infrared window material or support medium. The chapter presents many examples of spectra of inorganic compounds in the solid phase. The majority of these compounds are crystalline solids in which the crystallographic unit cell contains several polyatomic ions or molecules. Optical modes called lattice modes of vibration result from the motion of one polyatomic group relative to another within the unit cell. Lattice modes occur in the region 400–10 cm−1 and are characteristic of specific crystal geometry. They are used as fingerprints for an inorganic compound in much the same way as the internal modes of vibration of organic compounds are used in the region 4000–400 cm−1.