Transmission infrared spectroscop

The VT-DRIFT spectrum of pyridine adsorbed on unmodified silica gel is shown in Figure 29.3, Absorption maxima are observed at 1595, 1485, and 1445 cm According to the assignments made by Parry [16], these bands indicate hydrogen-bond formation. The absorptions result from in-plane C-C stretching modes 8a, 19a, and 19b, respectively [18]. The acidic strength of the surface sites is insufficient to generate pyridinium ion. This observation is consistent with previous studies of silica gel that used transmission infrared spectroscopic techniques [19]. 

Transmission infrared spectroscopic investigations of the interaction of PH3 with Alg03-supported Rh surfaces indicated that PH3 initially adsorbs in a molecular state at 90 K and decomposes to PHg and PH at 100 K, probably via an intermediate hydrogen-bonded chemisorbed state of molecular PH3 [44]. PH3 can displace CO on these surfaces, and the formation of Rh(CO)PH3 was verified spectroscopically [45]. Displacement of CO or NO by PH3 was also found on Rh(IOO) surfaces [43]. 

The present-day literature contains many more spectra obtained from singlecrystal metal surfaces by VEELS than by RAIRS. However, the much higher resolution available from the more recently developed RAIRS technique and its capability of operating in the presence of a gas phase suggest that it will contribute increasingly important information in the hydrocarbon adsorption field. The three spectroscopic techniques discussed above are much the most important ones in this area, with transmission infrared spectroscopy as the predominantly useful one for work with finely divided samples. A few other vibrational spectroscopic techniques (25) have provided information on adsorbed hydrocarbons, but are at present of more limited or specialized applications. Their principal characteristics are more briefly summarized below. 

G. E. Ritchie, E. W. Ciurczak, H. L. Mark, Validation of a Near-Infrared Transmission (NIT) Spectroscopic Assay of Sustained Release Prescription Analgesic Tablets, Proc. PittCon, New Orleans, March, 2000. 

Ritchie, G. E., Ciurczak, E. W, and Mark, H. Validation of a near-infrared transmission (NIT) spectroscopic assay of sustained-release prescription analgesic tablets. In Pittsburgh Conference of Analytical Chemistry and Applied Spectroscopy, March 2000, New Orleans, LA. 

Monocrystals of cesium bromide or cesium iodide are used as lenses in infrared spectroscopes according to their infrared transmission characteristics. Occasionally, cesium halogenide-monocrystals are used in scintillation techniques for a- or 3-spec-troscopy. 

Solid samples not only come in many diverse physical forms (powders, granules, fibers, films, sheet, biological tissue, etc.), but they may also be presented for examination in a wide variety of ways, and analyzed by a range of techniques that include both transmission and reflection methods. In the infrared spectroscopic examination of solids, due attention and consideration must be given to a number of factors. 

Solid samples for infrared spectroscopic measurements are frequently in the form of a powder. It is impossible to measure directly an infrared transmission spectrum from a powder sample, because powder strongly scatters the infrared light. To measure an infrared tfans-mission spectrum from a powder sample, it is a usual practice to disperse the powder sample in a medium (KBr, liquid paraffin, etc.) to reduce the scattering. 

Water vapor transmission by modulated infrared spectroscopic methods... 

The interface properties can usually be independently measured by a number of spectroscopic and surface analysis techniques such as secondary ion mass spectroscopy (SIMS), X-ray photoelectron spectroscopy (XPS), specular neutron reflection (SNR), forward recoil spectroscopy (FRES), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), infrared (IR) and several other methods. Theoretical and computer simulation methods can also be used to evaluate H t). Thus, we assume for each interface that we have the ability to measure H t) at different times and that the function is well defined in terms of microscopic properties. 

In some techniques, including XRD, some IR spectroscopic techniques, and neutron activation, the surface of the soil sample is analyzed using radiation reflected or emitted from the sample. In the other types of spectroscopy, such as NMR, information is obtained from radiation passing through the sample. Infrared spectroscopy (both NIR and MIR) can be used in both transmission and reflection analyses. 

Instrumentation developments in the 1920 s and 30 s led to a rapid expansion of spectroscopic methods in the laboratory (28, 34-39). These included further penetration into the infrared regime and some applications to infrared transmission in the atmosphere. Additional equipment was developed during World War II as a result of military requirements. This period was a fruitful one for the science of spectroscopy, and saw the first applications of infrared equipment as gas measurement tools (40-41) and as routine process controllers (42). 

A. R. H. Cole, Tables of Wavenumbers for the Calibration of Infrared Spectrometers, 2d ed., Pergamon, Oxford (1977). See also http //www.hitran.com/ (HITRAN is a compilation of spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of infrared light in the atmosphere.)... 

Kaneko, K., Shirai, O., Miyamoto, H., Kobayashi, M. and Suzuki, M. (1994c). Oblique infrared transmission spectroscopic study on the E C and B C phase transitions of stearic acid effects on polytypic structure. J. Phys. Chem., 98, 2185-91. [129]... 

Altered surfaces have been inferred from solution chemistry measurements (e.g., Chou and Wollast, 1984, 1985) and from spectroscopic measurements of altered surfaces, using such techniques as secondary ion mass spectrometry (for altered layers that are several tens of nm thick (e.g., Schweda et al, 1997), Auger electron spectroscopy (layers <10 nm thick (e.g., Hochella, 1988), XPS (layers <10 nm thick (e.g., Hochella, 1988 Muir et al, 1990), transmission electron microscopy (TEM, e.g., Casey et al, 1989b), Raman spectroscopy (e.g.. Gout et al, 1997), Fourier transform infrared spectroscopy (e.g., Hamilton et al, 2001), in situ high-resolution X-ray reflectivity (Farquhar et al, 1999b Fenter et al, 2003), nuclear magnetic resonance (Tsomaia et al, 2003), and other spectroscopies (e.g., Hellmann et al, 1997). 

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