Infrared reflection adsorption spectroscopy IRRAS

Another class of techniques monitors surface vibration frequencies. High-resolution electron energy loss spectroscopy (HREELS) measures the inelastic scattering of low energy ( 5eV) electrons from surfaces. It is sensitive to the vibrational excitation of adsorbed atoms and molecules as well as surface phonons. This is particularly useful for chemisorption systems, allowing the identification of surface species. Application of normal mode analysis and selection rules can determine the point symmetry of the adsorption sites./24/ Infrarred reflectance-adsorption spectroscopy (IRRAS) is also used to study surface systems, although it is not intrinsically surface sensitive. IRRAS is less sensitive than HREELS but has much higher resolution. 

Within catalysis and surface science, vibrational spectroscopy techniques are important tools to identify adsorbates, study their binding behavior, can provide information on adsorption sites. In the case of infrared spectroscopy, the most common form of vibrational spectroscopy, the vibrations in molecules are excited by the absorption of photons in the infrared range. Since the IR has only been used for few measurements within this work the experimental setup is described below but no theory is presented here, but can be found elsewhere [37, 101-104]. In order to measure infrared adsorption spectra on single crystal surfaces, a variation of IR spectroscopy is used, called infrared reflection adsorption spectroscopy (IRRAS). A schematic sketch of the IRRAS setup of the nanocat is depicted in Fig. 3.11. 

Application of advanced microscopic and spectroscopic methods, such as Brewster Angle Microscopy (BAM), Infrared Reflection-Adsorption Spectroscopy (IRRAS) and Grazing Incidence X-ray Dififaction (GIXD) at the monolayer revealed that when two lipid phases coexist, only the disordered liqnid-expanded phase is affected by the ions. Table I snm-marises GIXD results for the crystal cell parameters of the ordered liquid-condensed phase. These results prove that the ordered DPPC phase is not strongly affected by salts even at high salt concentrations. 

While the orientations evident from x-ray diffraction are not singularly specific for each monolayer, the x-ray data clearly indicate that the orientation of the crystals depends upon the chemical nature of the terminal functional group of the monolayer. This result was also confirmed using grazing angle infrared reflection adsorption spectroscopy (IRRAS).(79) It is reasonable to suggest that this behavior is a consequence of interfacid interactions during the nucleation process. 

Adsorption of the enzymes subtilisin BPN and lysozyme onto model hydrophilic and hydrophobic surfaces was examined using adsorption isotherm experiments, infrared reflection-absorption spectroscopy (IRRAS), and attenuated total reflectance (ATR) infrared (IR) spectroscopy. For both lysozyme and BPN, most of the enzyme adsorbed onto the model surface within ten seconds. Nearly an order-of-magnitude more BPN adsorbed on the hydrophobic Ge surface than the hydrophilic one, while lysozyme adsorbed somewhat more strongly to the hydrophilic Ge surface. No changes in secondary structure were noted for either enzyme. The appearance of carboxylate bands in some of the adsorbed BPN spectra suggests hydrolysis of amide bonds has occurred. 

Although optical vibrational techniques are less sensitive than electron-based spectro-metric methods, these techniques are employed extensively for thin-film characterization because of the specific and characteristic vibrational spectrum shown by various functional groups and molecules present in the film. The most commonly used vibrational spectroscopic techniques are infrared (IR) and Raman spectroscopy. Because of the interference caused by absorption of IR by the underlying substrate, IR reflection-adsorption spectroscopy (IRRAS) and its polarization modulation (PM) analog, PM-IRRAS, which uses the polarization selectivity of surface adsorption, are typically employed to characterize thin films (Gregoriou and Rodman, 2006). 

Infrared Reflection-Absorption Spectroscopy (IRRAS), In this method, the signal is obtained as a true infrared band. A useful comparison between EMIRS and IRRAS signals was made by Russell et for the case of the adsorption of CO on a smooth platinum electrode in acid solution. The result (Figure 14) is a good demonstration of the origin of the particular shape of the EMIRS bands. 

During this work, we analyzed the organization, the morphology, and the preferential adsorption of these copolymers and how these properties would be influenced by the interfacial interactions that could be established between the polymer and the chemical functionalities grafted onto the adsorption substrate. Our results were mainly based on two surface techniques polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and atomic force microscopy (AFM). 

A prerequisite for the development indicated above to occur, is a parallel development in instrumentation to facilitate both physical and chemical characterization. TEM and SPM based methods will continue to play a central role in this development, since they possess the required nanometer (and subnanometer) spatial resolution. Optical spectroscopy using reflection adsorption infrared spectroscopy (RAIRS), polarization modulation infrared adsorption reflection spectroscopy (PM-IRRAS), second harmonic generation (SFIG), sum frequency generation (SFG), various in situ X-ray absorption (XAFS) and X-ray diffraction spectroscopies (XRD), and maybe also surface enhanced Raman scattering (SERS), etc., will play an important role when characterizing adsorbates on catalyst surfaces under reaction conditions. Few other methods fulfill the requirements of being able to operate over a wide pressure gap (to several atmospheres) and to be nondestructive. 

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