Fourier transform infrared measurable spectral region

This method measures total unsaturation in a sample by the multivariate analysis of Fourier transform infrared spectra. It correlates the absorbance in the spectral regions corresponding to two major types of unsaturation with their concentrations. This is an extension of univariate least squares analysis that correlates a single band absorbance height or area with concentration. 

In Chapters 2 to 8 we describe the theory and instrumentation needed for an appreciation of the way that Fourier transform infrared and Raman spectra are measured today. The sampling techniques for and applications of FT-Raman spectrometry are described in Chapter 18. The remaining chapters cover the techniques and applications of absorption, reflection, emission, and photoacoustic spectrometry in the mid- and near-infrared spectral regions. 

A high-resolution fourier-transform interferometer (FTIR) which measures the spectral absorption due to the presence of infrared-active gases across the entire spectral region from 1 to 15 xm. This is interfaced to a multi-pass optical-absorption gas cell, which provides a path length of up to 120 m to enable gas detection with high sensitivity. 

Terahertz (THz) spectroscopy systems utilize far-infrared radiation to extract molecular spectral information in an otherwise inaccessible region of the electromagnetic spectrum where various rotational, vibrational, and translational modes of molecules are located, 0.1-10 THz (Fig. 1). As the wavenumber range is narrowed, THz-radiation can yield more specific information about a particular chemical component within the system. Unlike most spectroscopic techniques, THz instrument measures the wave temporal electric field, which can be Fourier transformed to yield THz pulse amplitude and phase. This added capability allows precise... 

Infrared spectra were recorded in the reflectance mode on a Fourier-transform Bruker IFS 113v spectrometer. The appropriate sources, beam splitters and detectors were utilized to cover effectively the 30-5,000 cm spectral range. Reflectance spectra In the nir-vis-uv region (4,000-40,000 cm" ) were recorded on a Varian 2390 spectrometer. Raman spectra were measured on a Ramanor HG 2S Jobln-Yvon spectrometer. To avoid sample decomposition, care was taken to maintain the Incident laser power as low as possible ( <20 mW), and have the sample In the spinning pellet form. 

The multiplex advantage is important enough so that nearly all infrared spectrometers are now of the Fourier transform type Fourier transform instruments are much less common for the ultraviolet, visible, and near-infrared regions, however, because signal-to-noise limitations for spectral measurements with these types of radiation are seldom a result of detector noise but instead are due to shot noise and flicker noise associated with the source. In contrast to detector noise, the magnitudes of both shot and flicker noise increase as the radiant power of the signal increases. Furthermore, the total noise for all of the resolution elements in a Fourier transform measurement tends to be averaeed... 

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