Multiple attenuated internal reflection

The Infrared Internal Reflectance Approach An interesting alternative method of minimizing the solution path-length is to employ internal reflectance or attenuated total reflectance (ATR) and this was the approach adopted by the authors of the first report on the acquisition of in situ infrared spectra Mark and Pons [39] employed the ATR approach, [or, as they termed it, frustrated multiple internal reflection (MIR)-see below], to... 

Solid state spectra can be measured by the Attenuated Total Reflectance or Multiple Internal Reflection methods as well as by simple transmission techniques (222). Brooker (223) has reported the discovery of the translational vibrations of NaN02, NaNOs, and CaCOs (calcite). The orientation of the bonds in (U02)(N0s)2. 6 H2O has been ascertained from the spectra obtained in this manner (223). 

The most commonly used technique for obtaining a spectrum is the attenuated total reflectance (ATR) method in the multiple internal reflectance (MIR) mode. In this method, the infrared beam is passed into a special crystal of a selenide (KRS-5). The angle of incidence is such that the beam will bounce along the crystal. A sample of the polyurethane is placed hard up against the crystal. The infrared just penetrates into the material before it continues down the crystal. A number of internal bounces are obtained along the crystal. Up to 25 reflectances are obtained from a 2 mm crystal. Figure 9.8 illustrates the infrared path in an ATR cell. 

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)... 

IR spectroscopy is a common analytical technique in the textile industry. IR is capable of identifying fibers and their additives, as well as showing quantitative blend ratios and additive contents. The ATR (attenuated total reflection) technique, especially in its multiple form, MIR (multiple internal reflection) is of special importance in this field. The sample preparation is simple and fast the cut out swatches with appropriate surface areas are placed against each side of the MIR crystal, ensuring sufficient and uniform contact across the crystal surface. The internal reflection methods are non-destructive, so that the sample may be saved for other types of analysis, they are, further, methods of surface analysis. This is advantageous in all cases where the finish resides primarily on the fiber surface. In this case, a very strong spectrum of the finish is obtained, with minimal interference from the base fiber (Hannah et al., 1975). 

The sample absorbs the evanescent field so that the totally reflected wave is attenuated accordingly the reflectance spectrum closely resembles a transmission spectrum. Usually such spectra can actually be inteipreted and evaluated as transmittance, and commercially available accessories are designed to support this. With angles of reflection well above the critical one, some sensitivity is lost which however is regained by multiple internal reflections. How pronounced the actual spectrum is, can be adjusted by the number of reflections used, i.e. the sample-coated area of the slab whether both surfaces, one surface, or just a fraction. In any case the area of a given reflection should fully be covered to avoid spectral dilution. 

The second case refers to the so-called Internal Reflection Spectroscopy, that is used in the so-called Attenuated Multiple Total Internal Reflection technique... 

Adsorption of CN on a silver metal film was reported by Hatta et al. [112], using multiple internal reflection in an ATR (attenuated total reflection) prism configuration. Basically the same features were observed by Hatta et al. as in the external reflection approach, namely a potential-dependent band located between 2100 and 2118 cm assigned to the adsorbed CN ion and another band located at 2143 cm , assigned to the Ag(CN)2 complex. The feature at 2167 cm was not observed, because of the limited potential range used in this experiment to avoid the dissolution of the silver film [112]. 

These investigations were aided substantially by use of the multiple attenuated internal reflection (MAIR) spectroscopic technique to record surface specific, infrared (IR) spectra in order to determine structure and monitor preparation and cleaning methods. 

Only the methods used in this study (i, 2, 3) can detect and follow the initial events at the boundary between a solid substrate and the biological milieu. This extraordinary sensitivity derives from the ability to monitor events from within the substrate itself by making the substrate capable of supporting multiple attenuated internal reflection (MAIR) at a variety of useful spectroscopic wavelengths. In other studies, it was concluded that adsorbed protein on solid substrates is of essentially native i.e. solution or volume phase) conflguration and present in signiflcant thickness (6). Those studies used a different version of the internal reflection spectroscopic method wherein a prism element was forcefully... 

Another approach, internal reflection spectroscopy (IRS) or attenuated total reflectance (ATR) spectroscopy, takes advantage of the total reflection observed when a light beam is directed to the back of the OTE at an angle greater than the critical angle. Since the reflection takes place at the electrode-solution interface, the light beam is attenuated only by molecules close to the electrode surface. The penetration depth is about 1000 A in a typical experiment. Because of this very small effective cell length, the electrode is most frequently used in a multiple reflection mode [Fig. 44(b)]. 

The main problem in IR measurements in situ is a strong IR absorption by the solvent water. Therefore the measurements in the classical transmission mode are practically excluded (the path length must not exceed 15 tan). Short path lengths are provided by the attenuated total reflection (ATR) mode. The probing light beam undergoes multiple total internal reflection in the ATR element (e.g. a cylindrical rod made of ZnSe, with two cone-sharpened ends) and each reflection... 

Infrared spectra can also be obtained by reflecting the IR beam on the surface of a sample. This technique is applied when it is not possible to obtain an IR spectrum by a transmission technique. Attenuated total reflectance (ATR) also known as ATIR (attenuated total internal reflectance) is based on multiple internal reflectance of the IR beam on the sample surface using a high refractive index crystal (e.g.. 

Fig. 4. Removal of an organic fatty acid monolayer on a water surface by a rising hydrophilic plate after the method of Blodgett (1934,1935) and its analysis by multiple attenuated internal reflection (Baier, 1970). Reproduced with permission of the author.

Figure 17-1.1 shows an apparatus for AI R measurements. Ascan be. seen from the upper figure, the sample (here, a solid) is placed on opposite sides of a transparent crystalline material of high refractive index. By proper adjustment of the incident angle, the radiation undergoes multiple internal reflections before passing from the crystal to the detector. Absorption and attenuation take place at each of these rellections. 

Raman spectra of acidic aqueous solutions of M0C12-8H20 (M = Zr or Hf) have been examined in an effort to detect the zirconyl and hafnyl ions, M=0. No evidence for a v(M=0) Raman band in the region 800-1000 cm was found. A broad IR band centered at 1000 cm" is observed in the multiple attenuated internal reflectance spectrum of a concentrated ZrOCL solution. " However, this band shifts to lower frequency upon deuteriation, indicating that the solution species contains hydroxo bridges, and not zirconyl groups. Bands due to 6(ZrOH) in the 910-1030 cm region of the IR spectrum of crystalline... 

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