Reflection infrared spectra measurements

Internal reflection infrared spectra measured in situ during etching of silicon in HF solutions exhibit characteristic Si - H modes, although the Si - H spectrum is broad because of interaction of the surface Si-H groups with the electrolyte. No electrochemical or chemical intermediate species have been detected [112]. Infrared spectra of porous silicon layers after drying reveal characteristic Si-H and Si-H2 peaks similar to the spectra obtained for hydrogen on Si(lOO) 2x1 surfaces [112]. 

To examine the resulting membrane, the reflective infrared spectrum of this membrane was measured. It was found that the absorption band at 1060 cm observed in the sulfonic acid-type membrane disappeared, and a strong absorption band corresponding to the sulfonyl chloride group was observed at 580 and 1420 cm . ... 

The same membranous material as mentioned in 1) having a thickness of 100 jjl was set in a reactor of the design which would allow only one surface of the membrane to contact with reaction reagents. Thereafter, the reactor compartment was filled with vapour of phosphorous pentachloride ( at 170°C for an hour ) to have one surface of the membrane reacted. The reflective infrared spectrum and dyeing test respectively showed that the membrane had sulfonyl chloride groups and that approximately 5 JJL of non-dyed layer was stratified at the membrane surface where phosphorous pentachloride had contacted. The electric resistance of this membrane was about 1500 ft- cm2 in a 1.0 N hydrochloric acid solution at 25°C when measured by 1000 cycle A.C. The electric resistance of the same membrane before the reaction with phosphorous pentachloride was only 0.38ft - cm2 under the same conditions. 

On the other hand, the electric resistance of the membrane before the reaction with phosphorous pentachloride and triethylamine was 1,1 - cm2 and l,0i2- cm2 respectively when measured in the environment of 3,5 N sodium chloride solution to its one side and 6.0 N sodium hydroxide solution to the other side, and in the environment of 3.5 N sodium chloride solution of pH 0,5, According to reflective infrared spectrum, the absorption bands observed were different between the surfaces reacted with phosphorous pentachloride and non-reacted. Namely the absorption band at 1680cm 1 corresponding to carboxyl groups was observed, and the absorption band at 1060cm l observed in the sulfonic acid type membrane disappeared on the surface which had been reacted with phosphorous pentachloride. 

Define Iq to be the intensity of the light incident upon the sample and I to be the intensity of the beam after it has interacted with the sample. The goal of the basic inftared experiment is to determine the intensity ratio I/Iq as a function of the frequency of the light (w). A plot of this ratio versus the frequency is the infrared spectrum. The inftared spectrum is commonly plotted in one of three formats as transmittance, reflectance, or absorbance. If one is measuring the fraction of light transmitted through the sample, this ratio is defined as... 

An attempt to use the infrared spectrum of materials collected at the sea surface for a quantitative measure of composition has been made by Baier et al. [285]. They dipped a germanium crystal through the surface film, then ran an internal reflectance spectrum on the material clinging to the crystal. From the spectrum, they concluded that the bulk of the material present in the surface film was there as glycoproteins and proteoglycans. 

In the diffuse reflectance mode, samples can be measured as loose powders, with the advantages that not only is the tedious preparation of wafers unnecessary but also diffusion limitations associated with tightly pressed samples are avoided. Diffuse reflectance is also the indicated technique for strongly scattering or absorbing particles. The often-used acronyms DRIFT or DRIFTS stand for diffuse reflectance infrared Fourier transform spectroscopy. The diffusely scattered radiation is collected by an ellipsoidal mirror and focussed on the detector. The infrared absorption spectrum is described the Kubelka-Munk function ... 

Specular reflectance infrared involves a mirrorlike reflection producing reflection measurements of a reflective material or a reflection-absorption spectrum of a film on a reflective surface. This technique is used to look at thin (from nanometers to micrometers thick) films. 

For infrared measurements, cells are commonly constructed of NaCI or KBr. For the 400 to 50 cm 1 far-infrared region, polyethylene is a transparent window. Solid samples are commonly ground to a fine powder, which can be added to mineral oil (a viscous hydrocarbon also called Nujol) to give a dispersion that is called a mull and is pressed between two KBr plates. The analyte spectrum is obscured in a few regions in which the mineral oil absorbs infrared radiation. Alternatively, a 1 wt% mixture of solid sample with KBr can be ground to a fine powder and pressed into a translucent pellet at a pressure of —60 MPa (600 bar). Solids and powders can also be examined by diffuse reflectance, in which reflected infrared radiation, instead of transmitted infrared radiation, is observed. Wavelengths absorbed by the sample are not reflected as well as other wavelengths. This technique is sensitive only to the surface of the sample. 

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]. 

As a result, the depth of penetration, or effective pathlength, will be higher the greater X or the smaller the frequency. Therefore, an interferogram (raw infrared spectrum) is a measure of the attenuation of a trans fat test sample of the totally internally reflected infrared light. The interferogram of a reference background material (trans-free fat) is similarly measured. These are subsequently used to obtain an absorption spectrum. 

ATR is a technique based on total internal reflections at the crystal surface. The infrared spectrum is measured from a very thin volume surrounding the infrared transparent ATR crystal. This technique is one of the best IR sampling techniques suitable for analyses of chemicals in water. Detection limit is less than 1 mg/ml for nerve agents (10). 

An infrared spectrum can be analysed quantitatively by studying the variations in absorption wave-numbers, which reflect a change in environment, or the variations in the line intensities. To measure the latter it is necessary to use, depending on the transparency of the sample to the radiation, respectively, the Beer-Lambert law for transmission measurements and the Kubelka-Munk law for measurements using diffuse reflectance. 

Energies in the infrared spectrum are conventionally expressed in wave numbers, which are defined as the number of waves per centimeter, i.e., the reciprocal of the wavelength measured in centimeters. The infrared spectrum extends from 12,500 to 50 cm (i.e., a wavelength of 0.8-200 fjLia.) and the far infrared from 40-10 cm (260 p.m-1 mm), but the upper limit of most commercial instruments is about 200 cm (50 ixm). Spectra are most frequently obtained by absorption and reflection techniques, but polarization, emission, and luminescence are also used (C26). Similar components are used in all types of instrument. Reflection measurements of samples with low transmission are made in the near infrared with a conventional spectrophotometer fitted with a reflec-... 

Fig. 2 Comparison of near-infrared spectra of crystalline anhydrous glucose. Spectrum measured in transmittance using the KBr pellet technique [spectral resolution 64cm intensity data in absorbance (top trace) and diffuse reflectance spectrum using a spectral resolution of 32 cm and intensity data transformed to —log R) (bottom trace)].

The only piece of experimental evidence for the orientation of apoA-I helices on DMPC discoidal complexes has come from the use of polarized attenuated total reflection infrared (ATR-IR) spectroscopy (Brasseur et al. (1990 Wald et al., 1990). Although internal reflection spectroscopy is not new (Harrick, 1967), its combination with polarized IR measurements of oriented biological membranes is a more recent application, which allows the spectrum to be taken in the presence of water. The technique has been used most frequently to study the orientation of lipid functional groups relative to the membrane plane in pure lipid bilayers (Fringeli and Gunthard, 1981 Holmgre et al., 1987 Okamura et al., 1990 Hubner and Mantsch, 1991), but has also been applied to studies of... 

Hi) Most of the bands in the infrared spectrum of gallane vapor carry unmistakable signs of rotational structure no better example is provided than that of the two absorptions near 1980 cm" the appearance of which, as measured at moderately high resolution with the aid of a multiple reflection cell, is illustrated in Fig. 5. There are, it appears, two types of band. One type, exemplified by the band at 1976 cm S displays all the features characteristic of a parallel band of a highly prolate symmetric top molecule (see Section III.B.l). The other type has the attributes of a perpendicular band of such a molecule (as witness the band at 1993 cm in Fig. 5). 

Characterization of catalysts The zeolite structure was checked by X-ray diffraction patterns recorded on a CGR Theta 60 instrument using Cu Ka, filtered radiation. The chemical composition of the catalysts was determined by atomic absorption analysis after dissolution of the sample (SCA-CNRS, Solaize, France). Micropore volumes were measured by N2 adsorption at 77 K using a Micromeritics ASAP 2000 apparatus and by adsorption of cyclohexane (at P/Po=0.15) using a microbalance apparatus SET ARAM SF 85. Incorporation of tetrahedral cobalt (II) in the framework of Co-Al-BEA and Co-B-BEA was confirmed by electronic spectroscopy [18] using a Perkin Elmer Lambda 14 UV-visible diffuse reflectance spectrophotometer. Acidity measurements were performed by Fourier transform infrared spectroscopy (FT-IR, Nicolet FTIR 320) after pyridine adsorption. Self-supported wafer of pure zeolite (20 mg/cm ) was outgassed at 673 K for 6 hours at a pressure of lO Pa. After cooling at 423 K, the zeolite was saturated with pyridine vapour (30 kPa) for 5 min, evacuated at this temperature for 30 min and the IR spectrum was recorded. 

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