Near-Infrared, and Raman Spectroscopy

IR spectroscopy became widely used after the development of commercial spectrometers in the 1940s. Double-beam monochromator instruments were developed, better detectors were designed, and better dispersion elements, including gratings, were incorporated. These conventional spectrometer systems have been replaced by Fourier transform IR (FTIR) instrumentation. This chapter will focus on FTIR instrumentation and applications of IR spectroscopy. In addition, the related techniques of near-infrared (NIR) spectroscopy and Raman spectroscopy will be covered, as well as the use of IR and Raman microscopy. 

We also know that AZi = hv. When the frequency is high, A, is short and the energy of the radiation is high. 

It is common to use wavenumber, symbolized by either v or v, with units of cm-, in describing IR spectra. The first symbol is called nu tilde the second symbol is called nu bar both symbols are used in the literature. The unit cm is called a reciprocal centimeter. The wavenumber is the reciprocal of the wavelength. Wavenumber is the number of waves of radiation per centimeter, 1/X frequency is the number of waves per second, c/X. Wavelength and wavenumber are related by 

Both wavenumbers and wavelengths will be used throughout the chapter, so it is important to be able to convert between these units. The older IR literature used the term micron and the symbol p for wavelength in micrometers (pm). 

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Infrared, near-infrared, and Raman spectroscopy Vibrational spectroscopy (discussed in this chapter) X X Reaction monitoring Polymorphism Content determination Process monitoring (drying, granulation, blending)... 

IR spectrometry as described above is a really powerful tool to determine the structure of the H-bond network established by H2O molecules that are embedded in macromolecules. It is most certainly due to become a basic tool, as it gives unique information on this network. It is nevertheless not the only method that will be used in the future. Two other kinds of spectroscopic methods will certainly also be of interest. They are simpler methods NIR (near infrared) and Raman spectroscopies. These are routine methods that are complementary to IR spectrometry. 

Infrared, near-infrared, and Raman spectroscopy were used to study high density, linear low density (LLDPE), and low density polyethylene. Overlapping spectral bands were separated using the second derivative, principal component analysis, and two-dimensional correlation analysis. A model was developed, using partial least squares regression, to calculate the density of LLDPE. 1 ref. 

Applied Spectroscopy 53, No.5, May 1999, p.557-64 COMPARISON OF NEAR-INFRARED AND RAMAN SPECTROSCOPY FOR THE DETERMINATION OF CHEMICAL AND PHYSICAL PROPERTIES OF NAPHTHA Min-Sik Ku Hoeil Chung SK Corp. 

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