Infrared transmission spectroscopy

If i = i — ik] and H2 = ns — are known as a function of wavelength, Eq. 12 can be used to calculate the entire RAIR spectrum of a surface film. Since transmission infrared spectroscopy mostly measures k, differences between transmission and RAIR spectra can be identified. Fig. 6 shows a spectrum that was synthesized assuming two Lorentzian-shaped absorption bands of the same intensity but separated by 25 cm. The corresponding spectrum of i values was calculated from the k spectrum using the Kramers-Kronig transformation and is also shown in Fig. 6. The RAIR spectrum was calculated from the ti and k spectra using Eqs. 11 and 12 and is shown in Fig. 7. 

Langmuir-Blodged films have been deposited on many different substrates. The substrates used include different types of glass (such as quartz for UV-visible spectroscopy) CaF2 plates for transmission infrared spectroscopy silicon, germanium, and ZnSe plates for internal reflection infrared spectroscopy. For electrochemical applications, LB films... 

Transmission infrared spectroscopy is very popular for studying the adsorption of gases on supported catalysts and for studying the decomposition of infrared active catalyst precursors during catalyst preparation. Infrared spectroscopy is an in situ technique that is applicable in transmission or diffuse reflection mode on real catalysts. 

Huang H, Korzeniewski C, Vijayaraghavan G. 2002. Quantification of CO2 from electrochemical oxidation reactions with a strategy based on transmission infrared spectroscopy. Electrochim Acta 47 3675-3679. 

Infrared Spectroscopy Transmission Infrared Spectroscopy Diffuse Reflectance Infrared Spectroscopy (DRS, DRIFT) Infrared Emission Spectroscopy (IRES)... 

Several forms of infrared spectroscopy are in use, as illustrated in Fig. 8.4. The most common form of the technique is transmission infrared spectroscopy. In this case the sample consists typically of 10-100 mg of catalyst, pressed into a self-supporting disk of approximately 1 cm2 and a few tenths of a millimeter in thickness. Transmission IR can be applied if the bulk of the catalyst absorbs weakly. This is usually the... 

Transmission infrared spectroscopy is an important tool in catalyst preparation to study the decomposition of infrared-active catalyst precursors as a result of drying, calcination or reduction procedures. In particular, if catalysts are prepared from organometallic precursors, infrared spectroscopy is the indicated technique for investigation [26]. 

Note that in all the examples discussed so far, infrared spectroscopy gives its information on the catalyst in an indirect way, via hydroxyl groups on the support, or via the adsorption of probe molecules such as CO and NO. The reason why it is often difficult to measure the metal-oxide or metal-sulfide vibrations of the catalytically active phase in transmission infrared spectroscopy is that the frequencies are well below 1000 cm-1, where measurements are difficult because of absorption by the support. Infrared emission and Raman spectroscopy, discussed later on in this chapter, offer better opportunities in this respect. 

Ballinger, T.H., Wong, J.C.S., and Yates, J.T., Jr. (1992) Transmission infrared spectroscopy of high area solid surfaces. A usefid method for sample preparation. Langmuir, 8, 1575-1578. 

Morrissey 53) used transmission infrared spectroscopy to study protein adsorption onto silica particles in a heavy water (DzO) buffer. By observing the shift in the amide I absorption band, he could deduce the fraction of protein carbonyl groups involved in bonding to the silica surface. He found that bovine IgG had a bound fraction of 0.20 at low bulk solution concentrations, but only about 0.02 at high solution concentrations. However, neither prothrombin nor bovine serum albumin exhibited a change in bound fraction with concentration. Parallel experiments with flat silica plates using ellipsometry showed that the IgG-adsorbed layers had an optical thickness of 140 A and a surface concentration of 1.7 mg/m2 at low bulk solution concentration — in concentrated solutions the surface amount was 3.4 mg/m2 with a thickness of 320 A (Fig. 17). 

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. 

Overall perspectives of the results from ethene and the higher alkenes have been attempted in Sections VI.B.6 and VI.G. What has become clear, particularly in the context of hydrocarbon adsorption, is that the study of spectra on single-crystal surfaces is of great assistance in finding the correct interpretation of the more complex multispecies spectra obtained from finely divided metal catalysts. This has only become possible by the development of VEELS and RAIRS, the latter allied with the Fourier-transform methods that have also transformed the quality of the spectra from metal-particle catalysts obtained by transmission infrared spectroscopy. The use of RAIRS in turn has emphasized the general significance of the MSSR. 

Transmission Infrared Spectroscopy for High Surface Area Oxides... 

Interest in the vibrational spectra of adsorbed molecules is at least 40 years old. The past ten years have seen the development of many novel techniques for determining the vibrational spectra of adsorbed species and this symposium brings together a state-of-the-art survey of these techniques. In one s ethusiasm for the recent advances made in any subject there is a tendency to forget the parent technique and its steady contribution to our knowledge. In this case, the parent is simple transmission infrared spectroscopy. This paper, therefore, is an attempt to briefly present an overview of some of the developments which have occurred in the application of transmission infrared spectroscopy to surface studies with emphasis upon results generated in the past 10 years. For more detailed information on work published prior to 1967 the reader is referred to three texts which have appeared on this subject (1-3). 

The first application of transmission infrared spectroscopy to the study of adsorbed species appears to be the work of Buswell et at in 1938 (5). Those authors pressed a montmorillonite clay into a disc which was then "dried" at various temperatures. The spectra they obtained bear a remarkable similarity to many others that have been produced in the literature over the next forty years the authors were clearly able to resolve bands due to hydroxyl groups associated with the clay lattice and to adsorbed water which was slowly removed as a function of drying. 

In the limited space available this paper has attempted to give an overview of the ways that transmission infrared spectroscopy has been applied to the study of high surface area materials. Developments in improved sample preparation and the use of isotopic substitution have been discussed. The more quantitative aspect of work accomplished in the last decade has been emphasized by giving examples of adsorbtion isotherms on individual sites and the subsequent reactivity of the adsorbed molecules with these sites. 

Infrared spectroscopy Transmission infrared spectroscopy Diffuse reflectance infrared spectroscopy (DRIFTS) Attenuated total reflection (ATR)... 

The comparison of the spectra of stable molecules deposited on the drum of the cryostat with those obtained by normal transmission infrared spectroscopy show that the spectra observed from deposits on the drum are characteristic of transmission spectra rather than reflectance spectra. Since the matrices used have not been completely transparent blank runs have been necessary. 

Duerst, R.W. Duerst, M.D. Stebbings, W.L. Transmission infrared spectroscopy. In Modem Methods of Applied Molecular Spectroscopy John Wiley Sons New York, 1998. 

Two types of membrane supports were prepared because of their suitability for characterization by transmission infrared spectroscopy. One type is made by copolymerization of styrene and divinylbenzene (DVB, the crosslinking agent) and requires further functionalization prior to incorporation of the catalytic species. 

Schwarz, Russell, and Harnsberger have developed a technique combining transmission infrared spectroscopy and temperature-programmed desorption and used it to study the interaction of pyridine with three silica-aluminas. On the 10 wt % AI2O3, acid sites were calculated to be 0.27 [xmole m (84% Lewis acid sites under experimental conditions). The activation energies for... 

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