Reflection, attenuated total

The experimental apparatus consists of a gas flow system with a four-port valve, a multi-reflection Attenuated Total Reflection (ATR) accessory (Pike Technologies), and a custom reactor manifold mounted to the ATR top plate, shown in Fig. 45.1. The ATR reactor manifold consists of (i) a Cap2 window for UV irradiation, (ii) an inlet and outlet port, and (iii) an injection port for the liquid phase reactant. 

Internal reflectance (attenuated total reflectance ATR ). The internal reflectance or, more usually, attenuated total reflectance (ATR), technique depends on the total reflectance of an IR beam at the internal face of an IR-transparent crystal of high IR refractive index, as shown in Figure 2.38. Medium 1 is a prism of such a material (for example, Si, Ge or KRS-5 [thallous bromide- iodide]), medium 2 is a thin coating of a metal (Au, Pt, Fe) which forms the working electrode and medium 3 is the electrolyte. The... 

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 ... 

FT Spectrometers FT spectrometers (Figure 3) differ from scanning spectrometers by the fact that the recorded signal is an interferogram [14] (see Chapter 6.2). They can be coupled to a microscope or macrochamber with an FPA detector. FT chemical imaging systems (CISs) are available for Raman, NIR, and IR spectroscopy. However, they can only be considered as research instruments. For example, most IR imaging systems are FT spectrometers coupled to microscopes. This type of spectrometer allows the acquisition of spectra in reflection, attenuated total reflection (ATR), or transmission mode. 

Aspartic peptidases, 365 Atmospheric pressure chemical ionization (APCI), used with LC/MS ATR-FTIR. see Attenuated total reflection Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), trans fatty acids, 505-511 Autoxidation. see also Oxidation discussed, 535 of lipids, 558, 627 prevention of, 558... 

The first HWGs confined light to their core either by total internal reflection (attenuated total reflection guides) or by reflection off a metallic surface (leaky guides) as discussed in Sect. 2.3.1. The latest generation of HWGs is based on PBG materials as discussed in Sect. 2.3.2. 

Diffuse Reflectance, Attenuated Total Reflection or Multiple Internal Reflection, Photoacoustic (PAS), Photothemal Beam Deflection, Specular Reflection Absorption, and forensic applications with the diamond cell and the Fourier transform infrared (FTIR) microscope. In museum laboratories, FTIR applications have been used for problems of identification and degradation in art and archeology. (14)... 

Bertolucci, Jantzef, and Chamberlain (8) report briefly on their work using single-reflection, attenuated, total-reflection, infrared spectroscopy to study the mechanism of adsorption on hydroxy-apatite crystals of citric acid, tartaric acid, sodium citrate, oxytetracycline hydrochloride, and glycine. This work has been of interest to many chemists, but it also has particular pertinency to current research on dental adhesives and the effect of pretreatment of the tooth cavity wall. 

FTIR-ATR Fourier transform infrared reflection-attenuated total reflection... 

Changes in wheat carbohydrate chemistry due to chemical enzymatic degradation were measured on a macro scale by internal reflection (attenuated total reflection ATR) FT-IR spectroscopy from a spot size of 250 X 250 gm [51]. In this study, the absorption bands of sucrose, fructose, glucose, arabinose and galactose were identified, and spectra included for mahogany, huckleberry and oak, as well as for cellulose and cellophane. Both, principal component analysis (PCA) and plotting of PCI versus PC2 enabled distinctions to be made between filter paper, cello-... 

Total Internal Reflection (Attenuated Total Reflectance)... 

Measurement in the reflectance mode using either external specular reflection, internal reflection [attenuated total reflection (ATR)] or diffuse reflection... 

If medium 1 is absorbing, the evanescent field wiU be absorbed and less intensity can be reflected (attenuated total reflection (ATR)). An ATR spectrum is similar to the conventional absorption spectrum except for the band intensities at longer wavelengths. At longer wavelengths the evanescent field penetrates ever deeper into the sample, equivalent to an increasing sample thickness. Sometimes an empirical so-called ATR correction is appHed in order to compensate across the spectrum for the linear wavelength increase in Eq. (10) ... 

In principle, the sensor constructions rely on five basic sensing schemes transmission, reflection, grazing angle reflection, attenuated total reflection (ATR), and a variant of the ATR effect known as the fibre-evanescent wave sensor (FEWS) (Melting Thomson, 2002). The investigations described in chapters 3 and 4 are based on the use of the ATR technique, focusing on its advantageous properties, esp edally in terms of mechanical robustness. 

In internal reflection, at angles of incidence larger than the critical angle, electromagnetic radiation is totally reflected (attenuated total reflectance, ATR. see Section 16.2.2.4 and Fig. 5). This special ca.se is very important in analysis for two approaches. First, simple transportation of radiation within the fiber (or a waveguide). Second, in total reflection, an evane.scent field appears in which the electrical field vector decays exponentially in the optically less dense medium. Every change within the medium with lower refractive index influences the field vector coupled to the field in the optically denser medium. Therefore, the totally reflected radiation contains information about effects on the other side of the phase boundary (the medium with lower refractive index) [20], [144]. Various principles to interogate this effect are known and used in evanescent field sensors. 

A small-size target specimen will often need to be removed from a matrix in which it is buried by using a knife, scalpel, or needle in an appropriate and safe manner, depending on the conditions surrounding it. If the target specimen is covered by a layer of some other material this may need to be scraped off Infrared microscopic measurements are utilized in many areas of study. In order to satisfy the various needs, in addition to straightforward transmission measurements, various types of reflection measurements such as specular reflection, attenuated total reflection (ATR), and transmission-reflection measurements (described later) can be performed with an infrared microscope designed for such purposes. 

Owing to these improvements, infrared spectroscopy has undergone a marked development in the last few years because of the possibility of adapting new accessories to the spectrometers and, therefore, of analysing samples whose infrared spectrum was impossible to obtain some years ago. Among these accessories are those which can measure specular and diffuse reflection, attenuated total reflectance and microscopes. One area in which the technique has improved dramatically is forensic analysis. 

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