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Infrared transmission spectra

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. [Pg.134]

For some sample types, for example a coated substrate, it is not possible to collect an infrared transmission spectrum, whereas in some cases (e.g. when there are concerns over the effects of sample preparation) it may be more desirable to collect a reflected spectrum. The most popular reflection techniques nowadays are internal reflection spectroscopy (IRS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)... [Pg.292]

Figure 7 shows a portion of the infrared transmission spectrum for ... [Pg.83]

Liquids may be sampled as neat liquids or in solution. A mid-infrared transmission spectrum sufficient for chemical identification may often be recorded from a capillary layer of a nonvolatile, pure liquid. This may be prepared simply from a drop of the liquid that has been sandwiched between a pair of mid-infrared transparent windows clamped together, which is also resistant to attack by the liquid. A more reproducible (and safer) practice, however, is to use an appropriate pathlength cell. Whichever method is selected, the specimen examined must be free from bubbles. For strongly absorbing liquids and some quantitative applications, a more efficient approach may be to use an appropriate infrared internal reflection technique accessory. [Pg.2232]

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]... 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]...
Fig. 17. Infrared transmission spectrum for two thicknesses of polystyrene (33). 1 mil 25.4 jxm. Used with permission of Hanser Publications. Fig. 17. Infrared transmission spectrum for two thicknesses of polystyrene (33). 1 mil 25.4 jxm. Used with permission of Hanser Publications.
Figure 4.4 Quantitative (compositional) analysis of ethylene-vinyl acetate (EVA) copolymers A, infrared transmission spectrum of a 0.1 mm-thickness EVA copolymer film B, infrared absorbance spectra (offset for clarity) of a series of EVA copolymer films of 0.1 mm thickness C, infrared transmission spectrum of an EVA (32.3%) copolymer sample, 0.25 mm thickness D, infrared absorbance spectrum of an EVA (17.2%) copolymer sample, 4 mm thickness moulding ... [Pg.78]

Solid samples for infrared spectroscopic measurements are frequently in the form of a powder. It is impossible to measure directly an infrared transmission spectrum from a powder sample, because powder strongly scatters the infrared light. To measure an infrared tfans-mission spectrum from a powder sample, it is a usual practice to disperse the powder sample in a medium (KBr, liquid paraffin, etc.) to reduce the scattering. [Pg.21]

If a material could be made extremely thin, for example, to the level of a single layer of molecules, this thin layer would transmit almost all of the infrared radiation, so that its infrared transmission spectrum could be measured. In fact, it is possible to measure a mid-infrared transmission spectrum from a thin soap film. It is usually practically difficult, however, to maintain such a thin film without it being supported by a substrate. For a thin film supported on a substrate, its infrared spectmm is often obtained by utilizing a reflection geometry. Two reflection methods are available for measuring infrared spectra from substrate-supported thin films, depending on the dielectric properties of the substrates used. External-reflection (ER) spectrometry, which is the subject of this chapter, is a technique for extracting useful information from thin films on dielectric (or nonmetallic) substrates, while reflection-absorption (RA) spectrometry, described in Chapter 10, is effective for thin films on metallic substrates [1]. In addition to these two reflection methods, attenuated total-reflection (ATR) spectrometry, described in Chapter 13 and emission spectroscopy, described in Chapter 15 may also be useful in some specific cases. [Pg.127]

Figure 3 (A) Far-infrared transmission spectrum of chlorocy-clopropane (B) Raman spectrum of gaseous chlorocyclobutane. Figure 3 (A) Far-infrared transmission spectrum of chlorocy-clopropane (B) Raman spectrum of gaseous chlorocyclobutane.
Figure 17 Infrared transmission spectrum of a pyrolytic boron film deposited on a silicon substrate. The solid line and broken line correspond to the results of the author and Blum (48), respectively. Figure 17 Infrared transmission spectrum of a pyrolytic boron film deposited on a silicon substrate. The solid line and broken line correspond to the results of the author and Blum (48), respectively.
Infrared radiation from the light source is divided into two beams by the beam splitter. One beam is reflected onto a moving mirror and the other onto a stationary mirror. Both beams are then recombined and pass through the sample to the detector. Fourier transformation of the resulting interferogram yields an infrared transmission spectrum. [Pg.115]

From this equation it can be seen that the depth of penetration depends on the angle of incidence of the infrared radiation, the refractive indices of the ATR element and the sample, and the wavelength of the radiation. As a consequence of lower penetration at higher wavenumber (shorter wavelength), bands are relatively weaker compared to a transmission spectrum, but surface specificity is higher. It has to be kept in mind that the refractive index of a medium may change in the vicinity of an absorption band. This is especially the case for strong bands for which this variation (anomalous dispersion) can distort the band shape and shift the peak maxima, but mathematical models can be applied that correct for this effect, and these are made available as software commands by some instrument manufacturers. [Pg.536]

The ATR technique is a commonly used infrared internal reflection sampling technique. It samples only the surface layer in contact with the ATR element the sampling depth probed is typically of the order of 0.3-3 pm [1]. Unless software corrected, compared with a transmission spectrum, the relative intensity of bands within an ATR spectrum increase in intensity with decreasing wavenumber. Several FTIR instrument companies now supply "ATR-correction" software developed to correct for the different relative intensities of bands observed between ATR and transmission spectra, so that ATR spectra can be more easily compared to and searched against transmission spectra. [Pg.612]

Fig. 14. Infrared absorption spectrum of anode films prepared at Ts = 25°C with boron fractions xg = 0 (top), 0.25, 0.5 0.75, and 1 (bottom), respectively, in the gas. The film thickness and the transmission measured at v = 4000 cm-1 are given for each curve. From C.C. Tsai (1979). Fig. 14. Infrared absorption spectrum of anode films prepared at Ts = 25°C with boron fractions xg = 0 (top), 0.25, 0.5 0.75, and 1 (bottom), respectively, in the gas. The film thickness and the transmission measured at v = 4000 cm-1 are given for each curve. From C.C. Tsai (1979).
The infrared absorption spectrum of a compound expressed as transmission intensities at a number of different wavelengths. [Pg.368]

Infrared spectra of zeolitic samples can be measured in several different modes. These include transmission, diffuse reflectance, attenuated total internal reflection (ATR) and emission. Transmission and diffuse reflectance are by far the most widely used of these techniques. In the transmission mode, the sample is placed directly in the infrared beam of the instrument and the light passing through or transmitted is measured by the detector. This transmitted signal (T) is ratioed to the open beam (no sample) signal (To) to get the transmission spectrum of the sample. The transmission spectrum is converted to an absorbance spectrum ... [Pg.112]

At infrared wavelengths extinction by the MgO particles of Fig. 11.2, including those with radius 1 jam, which can be made by grinding, is dominated by absorption. This is why the KBr pellet technique is commonly used for infrared absorption spectroscopy of powders. A small amount of the sample dispersed in KBr powder is pressed into a pellet, the transmission spectrum of which is readily obtained. Because extinction is dominated by absorption, this transmission spectrum should follow the undulations of the intrinsic absorption spectrum—but not always. Comparison of Figs. 10.1 and 11.2 reveals an interesting discrepancy calculated peak extinction occurs at 0.075 eV, whereas absorption in bulk MgO peaks at the transverse optic mode frequency, which is about 0.05 eV. This is a large discrepancy in light of the precision of modern infrared spectroscopy and could cause serious error if the extinction peak were assumed to lie at the position of a bulk absorption band. This is the first instance we have encountered where the properties of small particles deviate appreciably from those of the bulk solid. It is the result of surface mode excitation, which is such a dominant effect in small particles of some solids that we have devoted Chapter 12 to its fuller discussion. [Pg.292]

Many polymers are too tough to be ground even at liquid nitrogen temperatures. Consequently, surface techniques are often used. Internal reflectance or attenuated total reflectance (ATR) is the second most commonly used infrared technique [38-40]. For soft or pliable polymers or solutions, ATR is an extremely versatile technique and the spectrum is similar to a transmission spectrum. Unlike transmission, the spectrum obtained is independent of sample thickness. [Pg.104]

Figure 20-29 Fourier transform infrared spectrum of polystyrene film. The Fourier transform of the background interferogram gives a spectrum determined by the source intensity, beamsplitter efficiency, detector response, and absorption by traces of H20 and C02 in the atmosphere. The sample compartment is purged with dry N2 to reduce the levels of H20 and C02. The transform of the sample interferogram is a measure of all the instrumental factors, plus absorption by the sample. The transmission spectrum is obtained by dividing the sample transform by the background transform. Figure 20-29 Fourier transform infrared spectrum of polystyrene film. The Fourier transform of the background interferogram gives a spectrum determined by the source intensity, beamsplitter efficiency, detector response, and absorption by traces of H20 and C02 in the atmosphere. The sample compartment is purged with dry N2 to reduce the levels of H20 and C02. The transform of the sample interferogram is a measure of all the instrumental factors, plus absorption by the sample. The transmission spectrum is obtained by dividing the sample transform by the background transform.
The pathlength of a cell for infrared spectroscopy can be measured by counting interference fringes (ripples in the transmission spectrum). The spectrum below shows 30 interference maxima between 1 906 and 698 cm-1 obtained by placing an empty KBr cell in a spectrophotometer. [Pg.450]

In emission spectrometry, the sample is the infrared source. Materials emit infrared radiation by virtue of their temperature. KirchhofF s law states that the amounts of infrared radiation emitted and absorbed by a body in thermal equilibrium must be equal at each wavelength. A blackbody, which is a body having infinite absorptivity, must therefore produce a smooth emission spectrum that has the maximum possible emission intensity of any body at the same temperature. The emissivity, 8, of a sample is the ratio of its emission to that of a blackbody at the same temperature. Infrared-opaque bodies have the same emissivity at all wavelengths so they emit smooth, blackbody-like spectra. On the other hand, any sample dilute or thin enough for transmission spectrometry produces a structured emission spectrum that is analogous to its transmission spectrum because the emissivity is proportional to the absorptivity at each wavelength. The emissivity is calculated from the sample emission spectrum, E, by the relation... [Pg.199]

Huvenne and Lacroix described a mathematical procedure for the correlation of band intensities of the Fourier-transform infrared absorption spectra with those of the corresponding infrared transmission spectra of compounds in KBr discs [22]. The procedure was applied to spectra of flunitrazepam, dipyridamole, and lactose that were obtained through the use of a Nicolet 7199 B FTIR spectrometer with photoacoustic detection. When the photoacoustic spectrum of a plant charcoal was used to correct the spectra for inequalities in the incident light flux before applying the procedure, the correlated band intensities were generally consistent with those obtained using infrared transmission spectra. The procedure may be useful for the direct identification of the drugs. [Pg.253]


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