Infrared transmission characteristics

Table 7.29 Infrared Transmission Characteristics of Selected Solvents...

TABLE 7.29 Infrared Transmission Characteristics of Selected Solvents Transmission below 80%, obtained with a 0.10-mm cell path, is shown as shaded area. 

Table A-5. Infrared transmission characteristics of spectroquality solvents commonly used in infrared spectroscopy in the 2... 16 pm region (5000... 625 cm ) for 0.1 mm solvent thickness . ...

TabIe-2.7 Infrared Transmission characteristics of selected solvents and Mulling Oils... 

Table-2.7 Infrared Transmission characteristics of selected solvents and Mulling Oils (Transmission below 80% obtained with a 0-10 mm cell path is given in cm ) ...

Monocrystals of cesium bromide or cesium iodide are used as lenses in infrared spectroscopes according to their infrared transmission characteristics. Occasionally, cesium halogenide-monocrystals are used in scintillation techniques for a- or 3-spec-troscopy. 

The following table lists the more common materials used for optical components (windows, prisms, etc.) in the infrared region of the electromagnetic spectrum. The properties listed are needed to choose the materials with optimal transmission characteristics.1 2 The thermal properties are useful when designing experiments for operation at elevated temperatures.3-5 This listing is far from exhaustive, but these are the most common materials used in instrumentation laboratories. 

Crystalline Phosphate Studies. On the basis of the results with triethyl phosphate, a series of calcium phosphates was examined by infrared spectrophotometry. Pertinent properties of these materials are summarized in Table II, and their spectral characteristics are shown in Table III. None of the synthetic hydroxyapatites [Caio(P04)e(OH)2] had the stoichiometric Ca/P ratio of 1.667, although they showed the apatite lattice structure. A typical infrared transmission spectrum (between 1500 and 700 cm.-1) of a dry powder synthetic hydroxyapatite is shown in Figure 1. 

This paper reviews the optical properties of undoped and activated fluoride glasses for the period 1985-1998. First, the infrared transmission, Rayleigh scattering, and refractive indices of several fluoride glasses are given and discussed. For the sake of completeness, fundamental physical characteristics such as thermo-mechanical properties are also given, although they may have been published before this period. 

Using matched cuvettes for solvent and analyte is seldom practical for infrared measurements because it is difficult to obtain cells with identical transmission characteristics. Part of this difficulty results from degradation of the transparency of infrared cell windows (typically polished sodium chloride) with use due to attack by traces of moisture in the atmosphere and in samples. In addition, pathlengths are hard to reproduce because infrared cells are often less than 1 mm thick. Such narrow cells are required to permit the transmission of measurable intensities of infrared radiation through pure samples or through very concentrated solutions of the analyte. Measurements on dilute analyte solutions, as is done in ultraviolet or visible spectroscopy, are usually difficult because there are few good solvents that transmit over appreciable regions of the infrared spectrum. 

Raman and other vibrational spectroscopies such as transmission, reflectance, or emission infirared can also provide valuable insight into the solid structure, particularly in the far infrared. The characteristic vibrational spectra of metal oxides and sulfides are often found in the 1200 to 100-cm l region of the infrared/Raman spectra. Changes in the oxide phases present and the formation of bulk sulfides may be detected in the far IR. 

The radiation absorption and transmission characteristics of polymers can be used to identify polymer types. The basic principle of spectrophotometric methods of analysis is to provide an energy source (such as infrared radiation, IR) to which a sample is exposed, and to convert to some measure a response that is characteristic of the moiecuies. This response is, most often, absorption of a fraction of the incident tight. 

Figure 1.18 A Infrared difference spectrum obtained by computer subtraction of the ATR-IR spectra of Compound 2 from Compound 6, B Infrared transmission spectrum of a thin film of the antiozonant on a NaCl plate. Checkmarks highlight those peaks characteristic of the pitra-phenylenediamine antiozonant Reproduced with permission from Waddell and co-workers. Rubber Chemistry and Technology [64]...

Single crystals of MgO have received attention due to their use in ductile ceramic studies. Extreme purity is required in this area. Periclase windows are also of potential interest in infrared applications due to their transmission characteristics. 

Infrared (IR) - The infirared spectrum is loosely defined as that portion of the electromagnetic continuum extending from the red visible (0.75 pm) to about 1000 pm. Because of instrument design considerations and the infirared transmission characteristics of the atmosphere, however, most infirared measurements are made between 0.75 and 20 pm. 

The chalcogenides are all insoluble in water and other common solvents. ZnSe and CdTe have excellent transmission characteristics. The only problem with these materials is their high refractive index, which leads to high front-surface reflectance (see Section 13.2.2), so that transmission spectra of liquids held in cells fabricated from these materials often give rise to interference fringes (see Section 11.1.3). These materials aU make excellent internal reflection elements. AMTIR (amorphous material that transmits infrared radiation) is a mixture of several chalcogenides. Many optical fibers used for mid-infrared spectrometry are made from this material (see Section 15.4). 

Infrared emission from a material contains information characteristic of the material, and the information is obtainable in a form that is basically equivalent to an infrared absorption spectrum. Depending on the purpose of analysis and the shape of the target of analysis, infrared emission spectroscopy measurements can be more informative or convenient than an infrared transmission or reflection spectroscopy measurement, which is described elsewhere in this book. Infrared emission spectroscopy provides a means for the remote detection and analysis of gases, for example, volcanic gas and flue gases [1]. 

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