Infrared spectroscopy reflectance measurements

Fourier transform infrared spectroscopy (EUR) measurements in the reflection absorption mode were performed in a small UHV chamber designed to... 

The polymer concentration profile has been measured by small-angle neutron scattering from polymers adsorbed onto colloidal particles [70,71] or porous media [72] and from flat surfaces with neutron reflectivity [73] and optical reflectometry [74]. The fraction of segments bound to the solid surface is nicely revealed in NMR studies [75], infrared spectroscopy [76], and electron spin resonance [77]. An example of the concentration profile obtained by inverting neutron scattering measurements appears in Fig. XI-7, showing a typical surface volume fraction of 0.25 and layer thickness of 10-15 nm. The profile decays rapidly and monotonically but does not exhibit power-law scaling [70]. 

Several properties of the filler are important to the compounder (279). Properties that are frequentiy reported by fumed sihca manufacturers include the acidity of the filler, nitrogen adsorption, oil absorption, and particle size distribution (280,281). The adsorption techniques provide a measure of the surface area of the filler, whereas oil absorption is an indication of the stmcture of the filler (282). Measurement of the sdanol concentration is critical, and some techniques that are commonly used in the industry to estimate this parameter are the methyl red absorption and methanol wettabihty (273,274,277) tests. Other techniques include various spectroscopies, such as diffuse reflectance infrared spectroscopy (drift), inverse gas chromatography (igc), photoacoustic ir, nmr, Raman, and surface forces apparatus (277,283—290). 

In this chapter, we have chosen from the scientific literature accounts of symposia published at intervals during the period 1920 1990. They are personal choices illustrating what we believe reflect significant developments in experimental techniques and concepts during this time. Initially there was a dependence on gas-phase pressure measurements and the construction of adsorption isotherms, followed by the development of mass spectrometry for gas analysis, surface spectroscopies with infrared spectroscopy dominant, but soon to be followed by Auger and photoelectron spectroscopy, field emission, field ionisation and diffraction methods. 

The material balance is consistent with the results obtained by OSA (S2+S4 in g/100 g). For oil A, the coke zone is very narrow and the coke content is very low (Table III). On the contrary, for all the other oils, the coke content reaches higher values such as 4.3 g/ 100 g (oil B), 2.3 g/ioo g (oil C), 2.5 g/ioo g (oil D), 2.4/100 g (oil E). These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands characteristic of C-H bands (3000-2720 cm-1), C=C bands (1820-1500 cm j have been measured. Examples of results are given in Fig. 4 and 5 for oils A and B. An increase of the temperature in the porous medium induces a decrease in the atomic H/C ratio, which is always lower than 1.1, whatever the oil (Table III). Similar values have been obtained in pyrolysis studies (4) Simultaneously to the H/C ratio decrease, the bands characteristics of CH and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C ratio may be comprised between 0.1 and 0.3 ... 

Various optical detection methods have been used to measure pH in vivo. Fluorescence ratio imaging microscopy using an inverted microscope was used to determine intracellular pH in tumor cells [5], NMR spectroscopy was used to continuously monitor temperature-induced pH changes in fish to study the role of intracellular pH in the maintenance of protein function [27], Additionally, NMR spectroscopy was used to map in-vivo extracellular pH in rat brain gliomas [3], Electron spin resonance (ESR), which is operated at a lower resonance, has been adapted for in-vivo pH measurements because it provides a sufficient RF penetration for deep body organs [28], The non-destructive determination of tissue pH using near-infrared diffuse reflectance spectroscopy (NIRS) has been employed for pH measurements in the muscle during... 

Carbon monoxide on metals forms the best-studied adsorption system in vibrational spectroscopy. The strong dipole associated with the C-O bond makes this molecule a particularly easy one to study. Moreover, the C-0 stretch frequency is very informative about the direct environment of the molecule. The metal-carbon bond, however, falling at frequencies between 300 and 500 cm1, is more difficult to measure with infrared spectroscopy. First, its detection requires special optical parts made of Csl, but even with suitable equipment the peak may be invisible because of absorption by the catalyst support. In reflection experiments on single crystal surfaces the metal-carbon peak is difficult to obtain because of the low sensitivity of RAIRS at low frequencies [12,13], EELS, on the other hand, has no difficulty in detecting the metal-carbon bond, as we shall see later on. 

Summarizing, infrared spectroscopy measures, in principle, force constants of chemical bonds. It is a powerful tool in the identification of adsorbed species and their bonding mode. Infrared spectroscopy is an in situ technique, which is applicable in transmission or diffuse reflection mode on real catalysts, and in reflection-absorption mode on single crystal surfaces. Sum frequency generation is a speciality... 

McCarty GW, Reeves JB III, Reeves VB, Follett RF, Kimble JM. Mid-infrared and near-infrared diffuse reflectance spectroscopy for soil carbon measurement. Soil Sci. Soc. Am. J. 2002 66 640-646. 

For n = 15 cereal samples from barley, maize, rye, triticale, and wheat, the nitrogen contents, y, have been determined by the Kjeldahl method values are between 0.92 and 2.15 mass% of dry sample. From the same samples near infrared (NIR) reflectance spectra have been measured in the range 1100 to 2298 nm in 2nm intervals each spectrum consists of 600 data points. NIR spectroscopy can be performed much easier and faster than wet-chemistry analyses therefore, a mathematical model that relates NIR data to the nitrogen content may be useful. Instead of the original absorbance data, the first derivative data have been used to derive a regression equation of the form... 

Fuller, M.P. and Griffiths, P.R. (1978) Diffuse reflectance measurements by Fourier-transform infrared spectroscopy. Anal. Chem., 50 (11), 1905-1910. 

Berardo, N. (1992) Measuring Italian ryegrass quality by near infrared reflectance spectroscopy (NIRS). In Murray, I. and Cowe, LA. (eds) Making Light Work Advances in Near Infrared Spectroscopy. VCH, Weinheim, Germany, pp. 272-276. 

Concentration profiles of H20m and OH after diffusion experiments can be measured by infrared spectroscopy. For the species profiles to reflect the concentrations at the experimental temperature and not altered during quench, the experimental temperature needs to be intermediate (usually 673 to 873 K) so that species reaction during quench is negligible. From such experiments, assuming Don and are independent of H20t, it is possible to fit all concentration... 

Modern infrared (IR) spectroscopy is a versatile tool applied to the qualitative and quantitative determination of molecular species of all types. Its applications fall into three categories based on the spectral regions considered. Mid-IR (MIR) is by far the most widely used, with absorption, reflection, and emission spectra being employed for both qualitative and quantitative analysis. The NIR region is particularly used for routine quantitative determinations in complex samples, which is of interest in agriculture, food and feed, and, more recently, pharmaceutical industries. Determinations are usually based on diffuse reflectance measurements of untreated solid or liquid samples or, in some cases, on transmittance studies. Far-IR (FIR) is used primarily for absorption measurements of inorganic and metal-organic samples. 

Infrared spectroscopy can provide a great deal of information on molecular identity and orientation at the electrode surface [51-53]. Molecular vibrational modes can also be sensitive to the presence of ionic species and variations in electrode potential [51,52]. In situ reflectance measurements in the infrared spectrum engender the same considerations of polarization and incident angles as in UV/visible reflectance. However, since water and other solvents employed in electrochemistry are strong IR absorbers, there is the additional problem of reduced throughput. This problem is alleviated with thin-layer spectroelectro-chemical cells [53]. 

The surface structure and acid sites of alumina-supported molybdenum nitride catalysts have been studied using temperature-programed desorption (TPD), and reduction (TPR), diffuse reflectance infrared spectroscopy, and X-ray diffraction (XRD) analysis. The nitride catalysts were prepared by the temperature-programmed reaction of alumina-supported molybdenum oxide (12.5% and 97.1%) with NH3 at temperatures of 773, 973, and 1173 K. TPR and XRD analyses showed that y-Mo2N was already formed at 973 K. On the basis of NH3-TPD measurements and IR spectroscopy, it was found that Lewis acid sites were predominant over Bronsted acid sites on the surface of Mo2N/A1203. 

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