Reflection-Absorption Spectroscopy IRRAS

The most probable orientation of the molecules onto a smooth metal surface can be inferred from reflection-absorption infrared spectroscopic IRRAS 

For a KBr pellet, a random orientation of crystallites exists in the solid, and the electric field of the IR radiation, perpendicular to the pellet, will excite both in plane and out of plane modes of the molecule. A solid film with a well defined molecular organization could produce IR spectra with different relative intensities for in plane and out of plane modes. Therefore, molecules arranged face-on to the smooth surface would strongly absorb the incident IR radiation normal to the surface through its plane molecular modes.  

the infrared and SEIRA, Raman and SERS and IRRAS measurements allow us to determine the most probable orientation of the molecules onto different metal surfaces, to infer about the influence that these surfaces have onto the molecular structure and to conclude about the mechanism governing the spectral enhancement in IR and Raman. 

Reflection-absorption infrared spectra (RAIRS) are in general recorded with P-polarized light at different incident radiation angles in the range 30-80°, by using commercial variable angle accessory mounted on the IR optical bench. 

Metal island films of controlled mass thickness are deposited in a commercial vacuum system evaporator using a glow discharge evaporation unit. The metal island films are in general fabricated onto preheated glass substrates. The film thickness is monitored using a commercial quartz crystal microbalance. 

---

K. and Enyo, M. (1989) Surface species produced on Pt electrodes during HCHO oxidation in sulfuric add solution as studied by infrared reflection-absorption spectroscopy (IRRAS) and differential electrochemical mass spectroscopy (OEMS)./. Electroanal. Chem., 258, 219-225. 

Some characteristics of, and comparisons between, surface-enhanced Raman spectroscopy (SERS) and infrared reflection-absorption spectroscopy (IRRAS) for examining reactive as well as stable electrochemical adsorbates are illustrated by means of selected recent results from our laboratory. The differences in vibrational selection rules for surface Raman and infrared spectroscopy are discussed for the case of azide adsorbed on silver, and used to distinguish between "flat" and "end-on" surface orientations. Vibrational band intensity-coverage relationships are briefly considered for some other systems that are unlikely to involve coverage-induced reorientation. 

SERS) (1) and several variants of infrared reflection-absorption spectroscopy (IRRAS) (2). ... 

The combination of surface enhanced Raman scattering (SERS) and infrared reflection absorption spectroscopy (IRRAS) provides an effective in-situ approach for studying the electrode-electrolyte interface. The extreme sensitivity to surface species of SERS is well known. By using polarization modulation of the infrared beam for IRRAS, the complete band shape is obtained without modulating the electrode potential. 

Infrared drying, ceramics processing, 5 656 Infrared dyes, 9 500 Infrared emission spectroscopy, 23 142 Infrared inks, 14 315 Infrared lasers, 22 180 Infrared LEDs, 22 175, 176 Infrared measurements, in growing amorphous silicon, 22 130 Infrared microspectroscopy, 16 486 Infrared reflection-absorption spectroscopy (irras), 24 72, 114-116. See also IR spectra... 

Ir spectra, of surface layers, 24 110. See also Infrared reflection-absorption spectroscopy (IRRAS) ir spectrometers, 23 132 Ir (infrared) spectroscopy, for analysis of MF resins, 15 790. See also Infrared technology Isanic acid, 5 34t... 

Electrochemists have used IR spectroscopy for many years to probe electrodeelectrolyte interfaces 107). The most popular technique is IR reflection absorption spectroscopy (IRRAS) 108). A schematic comparison of the principle of ATR and IRRAS experiments is shown in Fig. 37. One advantage of the ATR over the IRRAS technique for catalytic applications concerns diffusion. In IRRAS experiments, the IR beam passes through a thin liquid film between a window and the sample. This... 

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. 

With infrared reflection absorption spectroscopy (IRRAS), it is possible to obtain information about the orientation of enzyme molecules adsorbed on flat metal surfaces (3,4). Electric dipole-transition moments oriented perpendicular to a flat metal surface show enhanced IR absorbance. IR bands due to vibrations of groups with transition moments oriented parallel to the surface are not observed. The IR-beam component which is polarized perpendicular to the plane of incidence (parallel to the surface) contains no information and can be eliminated by using a polarizer. 

Infrared reflection-absorption spectroscopy (IRRAS) is done at fixed potential. Electric vectors in the incident beam parallel to the metal surface do not interact with adsorbed molecules, whereas those perpendicular to the surface do. The light beam is switched successively between the two directions and the results subtracted. 

IN SITU INFRARED REFLECTION ABSORPTION SPECTROSCOPY (IRRAS) OF LANGMUIR FILMS... 

Besides spectroscopic techniques such as infrared-reflection-absorption spectroscopy (IRRAS) and X-ray photoelectron spectroscopy (XPS), SFM-based stiffness imaging was applied in order to detect radiation-induced variations of surface stiffness [180]. For that purpose, when exposing the PE-film to the VUV-radiation, the film was covered with a Ni mesh. Thus, the PE-film was partially masked and exposed to the VUV radiation only within the square-shaped holes of the mesh. After having finished that treatment and having removed the mesh, the sample surface was scanned in force modula-... 

In the first case, it has been recognized that if molecules are adsorbed on the surface of a metal, only part of the grazing incident radiation is reflected, part being absorbed by the adsorbed species. This absorption is greatly increased if the incident radiation is polarized perpendicular to the metal surface. This is the basis of so-called Infrared Reflection Absorption Spectroscopy (IRRAS) [27], which is applied widely to surface studies on metal surfaces. In these conditions, an additional selection rule applies ... 

Information on the conformational state of the hydrocarbon chains and their orientation has been obtained from external infrared reflection absorption spectroscopy (IRRAS). The first systematic IRRAS studies on phospholipid Langmuir monolayers were reported by Dluhy et al ) (see, for instance fig. 3.62). For DPPC monolayers in the LE phase the positions of the conformation-sensitive symmetric and anti-symmetric C-H stretching bands in the IRRAS spectra were found to be at the same positions as for bilayer systems of DPPC above the Kralft temperature. In the LC phase the frequencies of these bands indicate that the hydrocarbon chains of the lipid molecules are in the all-trans ) conformation (i.e. zig-zag) and analysis of polarized IRRAS spectra show that their average tilt is ca 35° relative to the monolayer normal. This is in reasonable agreement with the tilt angle of 30° obtciined from X-ray diffraction on DPPC monolayers (30°). 

Figure 2.9a shows the lipid molecule DMPC. Two layers contacted via the hydrophobic tails lead to spontaneous formation of a double-layer biomimetic membrane that can be transferred to a single-crystal ultraplanar electrochemical Au(lll) surface. The hydrophilic head groups contact the electrode surface via an intermediate water film. Due to the structurally very well-defined assembly, not only AFM and in situ STM but also neutron reflectivity. X-ray diffraction, and infrared reflection absorption spectroscopy (IRRAS) have been employed to support the direct visual in situ STM. Electrochemically controlled structural changes, phase transitions, and the effects of the common membrane component cholesterol (Figure 2.9b) and peptide drugs have been investigated in this way. 

In the present study, the water surface is being surveyed by two optical methods, i.e., Brewster Angle Microscopy [BAM] and Infrared Reflection-Absorption Spectroscopy [IRRAS], A schematic sketch of the BAM... 

In previous studies [3, 4], we had pointed out that the interphase formation mechanisms result from dissolution of the metallic surface layers, concomitantly with ion diffusion through the liquid prepolymer. In order to detect the dissolution phenomenon, pure amine (either DETA or IPDA) was previously applied to chemically etched metallic sheets (either A1 or Ti alloys were used, and had hydroxidic surfaces). After 3 h, the metallic surfaces were scraped with a PTFE spatula. The modified amine (i.e., the amine reacted with the metal) was analyzed. Whatever the natures of the amine and the metal were, metal ions were detected in the modified amines by ICP analysis and new peaks were detected by infrared spectroscopy [5]. To indicate hydroxide dissolution, a very thin layer of liquid amine was applied to chemically etched aluminum, and Infrared Reflection - Absorption Spectroscopy (IRRAS) spectra were recorded every 5 min (the hydroxide band intensity variation at ca. 3430 cm was followed). The OH group peak intensity decreased when the amine-metal contact time increased [5]. Conversely, if pure DGEBA monomer was apphed to the metal surfaces, even after 3 h in contact with the metallic surfaces, no metal ion was detected by ICP in the DGEBA recovered, and the infrared spectra remained identical before and after the contact with the metal. Finally, if pure amine monomer was applied to gold-coated substrates, no chemical reaction was observed (by either IGP or FTIR analyses). 

This technique is used to study thin (down to submonolayer) films adsorbed on reflective substrates such as metals. Experimentally it involves measuring the change in the reflectance spectrum of the substrate that accompanies thin film formation. Various acronyms for the technique are used infrared reflection—absorption spectroscopy (IRRAS, IRAS) and reflection—absorption infrared spectroscopy (RAIRS). The Basics of IRRAS spectra are described in Chapter 5.2. 

---