Spectroscopy reflection

Absorption spectroscopy provides a means to study particular details about a monolayer. Transmission spectroscopy is difficult because the film, which is thin, absorbs little. Gaines [1] describes multiple-pass procedures for overcoming this problem. Reflection spectroscopy in the UV-visible range has been reported for lipid monolayers [150,151] and in the IR range for oleic acid [152]. 

Resonance Raman reflection spectroscopy of monolayers is possible, as illustrated in Fig. IV-14 for cetyl orange [157]. The polarized spectra obtained with an Ar ion laser allowed estimates of orientational changes in the cetyl orange molecules with a. 

Vibrational Spectroscopy. Infrared absorption spectra may be obtained using convention IR or FTIR instrumentation the catalyst may be present as a compressed disk, allowing transmission spectroscopy. If the surface area is high, there can be enough chemisorbed species for their spectra to be recorded. This approach is widely used to follow actual catalyzed reactions see, for example. Refs. 26 (metal oxide catalysts) and 27 (zeolitic catalysts). Diffuse reflectance infrared reflection spectroscopy (DRIFT S) may be used on films [e.g.. Ref. 28—Si02 films on Mo(llO)]. Laser Raman spectroscopy (e.g.. Refs. 29, 30) and infrared emission spectroscopy may give greater detail [31]. 

Attenuated total reflectance spectroscopy and reflection-absorption infrared spectroscopy... 

N. J. Harrick, Internal Reflection Spectroscopy, ]olm. Wiley Sons, Inc., New York, 1967. 

M. W. AT2rs1, Attenuated Total Reflectance Spectroscopy of Polymers Theory and Practice, American Chemical Society, Washington, D.C., 1996. 

DETERMINATION ORGANIC COMPOUNDS BY DIFFUSE REFLECTION SPECTROSCOPY... 

RAIRS spectra contain absorption band structures related to electronic transitions and vibrations of the bulk, the surface, or adsorbed molecules. In reflectance spectroscopy the ahsorhance is usually determined hy calculating -log(Rs/Ro), where Rs represents the reflectance from the adsorhate-covered substrate and Rq is the reflectance from the bare substrate. For thin films with strong dipole oscillators, the Berre-man effect, which can lead to an additional feature in the reflectance spectrum, must also be considered (Sect. 4.9 Ellipsometry). The frequencies, intensities, full widths at half maximum, and band line-shapes in the absorption spectrum yield information about adsorption states, chemical environment, ordering effects, and vibrational coupling. 

Harrick, N.J., Internal Reflection Spectroscopy. Interscience Publishers, New York, NY, 1967, p. 30. 

While electron or ion beam techniques can only be applied under ultra-high vacuum, optical techniques have no specific requirements concerning sample environment and are generally easier to use. The surface information which can be obtained is, however, quite different and mostly does not contain direct chemical information. While with infra-red attenuated total reflection spectroscopy (IR-ATR) a deep surface area with a typical depth of some micrometers is investigated, other techniques like phase-measurement interference microscopy (PMIM) have, due to interference effects, a much better surface sensitivity. PMIM is a very quick technique for surface roughness and homogeneity inspection with subnanometer resolution. 

In infra-red attenuated total reflection spectroscopy (IR-ATR) and grazing incidence reflection IR spectroscopy (IR-GIR) the evanescent wave of a totally... 

Other parameters which have been used to provide a measure of a include physical dimensions (thermomechanical analysis, TMA) [126], magnetic susceptibility [178,179], light emission [180,181], reflectance spectra (dynamic reflectance spectroscopy, DRS) [182] and dielectric properties (dynamic scanning dielectrometry, DSD) [183,184], For completeness, we may make passing reference here to the extreme instances of non-isothermal behaviour which occur during self-sustained burning (studied from responses [185] of a thermocouple within the reactant) and detonation. Such behaviour is, however, beyond the scope of the present review. 

Additional information concerning the mechanisms of solid—solid interactions has been obtained by many diverse experimental approaches, as the following examples testify adsorptive and catalytic properties of the reactant mixture [1,111], reflectance spectroscopy [420], NMR [421], EPR [347], electromotive force determinations [421], tracer experiments [422], and doping effects [423], This list cannot be comprehensive. Electron probe microanalysis has also been used as an analytical (rather than a kinetic) tool [422,424] for the determination of distributions of elements within the reactant mixture. Infrared analyses have been used [425] for the investigation of the solid state reactions between NH3 and S02 at low temperatures in the presence and in the absence of water. 

The application of diffuse reflectance spectroscopy to the chemistry of transition metal coordination compounds. E. L. Simmons, Coord. Chem. Rev., 1974,14,181-196 (81). 

Redox switching, 126 Reference electrodes, 100, 105, 142 Reflectance spectroscopy, 44 Resistance, 22, 105 Resolution 50, 71 Reverse pulse polarography, 68 Reversible systems, 4, 31 Reticulated vitreous carbon, 114, 115 Riboflavin, 37... 

In situ Fourier transform infrared and in situ infrared reflection spectroscopies have been used to study the electrical double layer structure and adsorption of various species at low-index single-crystal faces of Au, Pt, and other electrodes.206"210 It has been shown that if the ions in the solution have vibrational bands, it is possible to relate their excess density to the experimentally observed surface. 

Gutierrez, C. Potential-Modulated Reflectance Spectroscopy Studies of the Electronic Transitions of Chemisorbed Carbon Monoxide 28... 

Spherical rollers were machined from AISI 52100 steel, hardened to a Rockwell hardness of Rc 60 and manually polished with diamond paste to RMS surface roughness of 5 nm. Two glass disks with a different thickness of the silica spacer layer are used. For thin film colorimetric interferometry, a spacer layer about 190 nm thick is employed whereas FECO interferometry requires a thicker spacer layer, approximately 500 nm. In both cases, the layer was deposited by the reactive electron beam evaporation process and it covers the entire underside of the glass disk with the exception of a narrow radial strip. The refractive index of the spacer layer was determined by reflection spectroscopy and its value for a wavelength of 550 nm is 1.47. 

Some of the transition metal macrocycles adsorbed on electrode surfaces are of special Interest because of their high catalytic activity for dloxygen reduction. The Interaction of the adsorbed macrocycles with the substrate and their orientation are of Importance In understanding the factors controlling their catalytic activity. In situ spectroscopic techniques which have been used to examine these electrocatalytlc layers Include visible reflectance spectroscopy surface enhanced and resonant Raman and Mossbauer effect spectroscopy. This paper Is focused principally on the cobalt and Iron phthalocyanlnes on silver and carbon electrode substrates. 

Of special Interest as O2 reduction electrocatalysts are the transition metal macrocycles In the form of layers adsorptlvely attached, chemically bonded or simply physically deposited on an electrode substrate Some of these complexes catalyze the 4-electron reduction of O2 to H2O or 0H while others catalyze principally the 2-electron reduction to the peroxide and/or the peroxide elimination reactions. Various situ spectroscopic techniques have been used to examine the state of these transition metal macrocycle layers on carbon, graphite and metal substrates under various electrochemical conditions. These techniques have Included (a) visible reflectance spectroscopy (b) laser Raman spectroscopy, utilizing surface enhanced Raman scattering and resonant Raman and (c) Mossbauer spectroscopy. This paper will focus on principally the cobalt and Iron phthalocyanlnes and porphyrins. 

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