Infrared transmission mode

FIGURE 6.7 The infrared spectrum of a cocaine hydrochloride crystal obtained by flattening it with a roller, mounting it on an infrared transparent window, and measuring its spectrum using infrared transmission mode. 

The PLM can be used in a reflection or a transmission mode. With either mode, light of various wavelengths from ultraviolet to infrared, polarized or unpolarized, is used to yield a wide variety of physical measurements. With just ordinary white light, a particle or any object detail down to about 0.5 p.m (500 nm) in diameter can be observed to detect shape, size, color, refractive index, melting point, and solubiUty in a group of solvents, all nondestmetively. Somewhat larger particles yield UV, visible, or IR absorption spectra. 

In transmission mode a spatial resolution of about 15-20 pm can be achieved with infrared microscopes [32]. This is generally sufficient to properly identify such as small impurities, inclusions, gels or single components of multilaminate foils. Similar to Raman spectroscopy, line profiles or maps over larger sample areas can be performed. 

Measurements of supported catalysts in diffuse reflection and transmission mode are in practice limited to frequencies above those where the support absorbs (below about 1250 cm-1). Infrared Emission Spectroscopy (IRES) offers an alternative in this case. When a material is heated to about 100 °C or higher, it emits a spectrum of infrared radiation in which all the characteristic vibrations appear as clearly recognizable peaks. Although measuring in this mode offers the attractive advantage that low frequencies such as those of metal-oxygen or sulfur-sulfur bonds are easily accessible, the technique has hardly been explored for the purpose of catalyst characterization. An in situ cell for IRES measurements and some experiments on Mo-O-S clusters of interest for hydrodesulfurization catalysts have been described by Weber etal. [11],... 

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 ... 

Profile of the deposition of silicon alkoxlde was followed by an Infrared spectroscopy, Jasco FTIR-3 in a transmission mode. 

Conventionally, infrared spectroscopy is carried out in the transmission mode, where the light passes through a sample cell with a defined thickness. There are two main disadvantages of this technique for the purpose of reaction analysis. 

The sample thickness in the DIT cells (25 pm) is very large in comparison with the usual thickness of samples for infrared transmission studies, and the cell itself is also thick (2.8 mm). Studies in the attenuated total reflectance (ATR) mode do not fit the experiment. For all these reasons, it was by no means certain that infrared studies could in fact be performed using the existing DIT cells. 

Fourier-transformed infrared spectroscopy (FT1R), either in the transmission mode(70), the grazing incidence reflection (GI) mode(7,5) or the attenuated total reflection (ATR) mode(7,2), has been the most widely used experimental tool for the characterization and structure determination of SA monolayers. GI-IR is especially useful in determining the molecular orientation in the film structures because it senses only the vibrational component perpendicular to the substrate surface(7,5). Polarized ATR-IR can also be used to study molecular orientation(7,77). McKeigue and Gula-ri(72) have used ATR-IR to quantitatively study the adsorption of the surfactant Aerosol-OT. 

Reaction between LB films of Cd arachidate and ground state atomic oxygen, 0(3P), was investigated at various temperatures using FTIR spectroscopy [55,56]. Intensity of the CH2 stretching infrared band was monitored in a transmission mode and was found to decrease in the course of the reaction due to disappearance of the CH2 groups. 

On the other hand, far infrared transmission measurements [14] have found doublet splitting of the Flw(l) and Flu(2) modes and activation of silent odd modes already at room temperature. Because of the rapid timescale of the IR measurements, this suggests that there is a dynamic JTD at room temperature which becomes static below 140 K. Interestingly, a detailed x-ray diffraction study of this material [15] has evidenced an orientational transition at about the... 

Currently, several forms of infrared spectroscopy are in general use, as illustrated in Figure 8.4. The most common form of the technique is transmission infrared spectroscopy, in which the sample consists typically of 10 to 100 mg of catalyst, pressed into a self-supporting disk of approximately 1 cm2 and a few tenths of a millimeter thickness. Transmission infrared spectroscopy can be applied if the bulk of the catalyst absorbs weakly. This is usually the case with typical oxide supports for wavenumbers above about 1000 cm-1, whereas carbon-supported catalysts cannot be measured in transmission mode. Another condition is that the support particles are smaller than the wavelength of the infrared radiation, otherwise scattering losses become important. 

Indium nitride has twelve phonon modes at the zone centre (symmetry group Cev), three acoustic and nine optical with the acoustic branches essentially zero at k = 0. The infrared active modes are Ei(LO), Ei(TO), Ai(LO) and Ai(TO). A transverse optical mode has been identified at 478 cm 1 (59.3 meV) by reflectance [6] and 460 cm 1 (57.1 meV) by transmission [24], In both reports the location of a longitudinal optical mode is inferred from the Brout sum rule, giving respective values of 694 cm 1 (86.1 meV) and 719 cm 1 (89.2 meV). Raman scattering of single crystalline wurtzite InN reveals Ai(LO) and E22 peaks at 596 cm 1 and at 495 cm 1 respectively [25],... 

FTIR Spectroscopy. Infrared spectra were recorded on a Perkin Elmer Spectrum One FTIR spectrometer equipped with a Deuterated Triglycine Sulfate (DTGS) detector and KBr optics. Data collection was performed at 4 cm-1 spectral resolution in the region of 4000-450 cm-1 and averaged over 5 scans. All samples were measured in transmission mode. 

Infrared spectra were recorded on a Perkin-Elmer Model 983G double-beam spectrophotometer in the transmission mode using 3500 A thick PBTMSS films spin-coated and processed on polished NaCl plates. Spectral subtraction and absorbance correction to account for the decreased film thickness were used to isolate the silicon oxide absorption band at about... 

The infrared spectra were obtained using a commercial FTIR spectrometer (Mattson Centauri). The studies were performed in transmission mode, with the catalyst in the form of a pressed disc, using an environmental cell where the temperature, pressure, and gas composition could all be controlled [7]. All spectra were recorded at 4 cm resolution with the co-addition of 300 scans using an MCT detector. 

IR Spectra. The IR spectra of the SOG film were obtained with a Perkin Elmer Model 683 Infrared Spectrophotometer in transmission mode by passing radiation through the film coated on a single crystal silicon wafer. In order to enhance the spectral signal, three layers... 

The spectrum can usually be examined In-sltu (because the Raman can be in the reflective mode, whereas with Infrared, in the transmission mode, the specimen must be transferred to an Infrared transparent substrate - fortunately for silicon device work, silicon is transparent and usually particles can be analyzed in situ). 

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