Reflection-absorption spectrum

Figure 8.5. Palm of the hand. Fluorescence spectrum (Fb-mode, full line) and diffuse reflectance absorption spectrum (dashed line, normalized to X = 700 nm, reference filter paper) measured with a sensitized diode array spectrometer.

Specular reflectance infrared involves a mirrorlike reflection producing reflection measurements of a reflective material or a reflection-absorption spectrum of a film on a reflective surface. This technique is used to look at thin (from nanometers to micrometers thick) films. 

Theoretical consideration of the IR spectroscopy of monolayers adsorbed on a metal surface showed that the reflection-absorption spectrum is measured most efficiently at high angles of incidence, and that only parallel component of incident light gives measurable absorption species (23). Figure 4 presents a schematic description of a monomolecular film on a mirror, with the incident light and direction of the polarization. Figure 5 presents, in detail, an alkyl thiol molecule on a metal surface. Note the direction of the different transition dipoles. Thus, while both the... 

Figure 6. Transient (diffuse-reflectance) absorption spectrum (—) obtained at 25 ps following the 532-nm laser excitation of charge-transfer crystals of [CpFeCpCH2N+Mc3]2 M06O19 dispersed in neutral alumina (10 %). The spectrum is deconvoluted as the (1 1) sum of reduced hexamolybdate...

Complete back electron transfer upon charge-transfer excitation has also been observed in crystalline EDA complexes. For example, laser excitation of the charge-transfer crystals of ferrocenyl donor and polyoxomolybdate acceptor results in short-lived (ps) transients the diffuse-reflectance absorption spectrum of which is shown in Figure 6 [137]. This transient spectrum can be deconvoluted as the sum of the absorption spectra of the oxidized ferrocenyl donor (ferrocenium) and the re-... 

Fig. 27. Potential dependence of the IR reflection absorption spectrum of the linearly adsorbed CO on a platinum electrode in 5M CH3OH + 1M HC104.

Fig. 30. Change of the IR reflection absorption spectrum of the linearly adsorbed CO on a platinum electrode with potential (a) in the hydrogen region between 0.5 and 0.35 V (NHE) and (b) across the hydrogen region into the double layer region. Curve 1, 0.15 V (NHE) curve 2, 0.30 V (NHE) curve 3, 0.35 V (NHE) curve 4, 0.40 V (NHE) curve 5, 0.425 V (NHE) curve 6, 0.450V (NHE) curve 7, 0.475V (NHE) curve 8, 0.50 V (NHE).

The final in-situ infrared spectroelectrochemical technique was reported in a preliminary note in 1987 by Roe et al. [121], The paper reported the development of a new design of a spectroelectrochemical cell with a faster response time to enable the recording of transient IR spectra using the recently developed pulsed IR tunable lasers [122], A reflection-absorption spectrum was given of CO adsorbed on Pt at + 0.2 V (vs. SCE) in 1M HC104... 

The reflection-absorption spectrum of an Alq3 film deposited on Si with Au precoat shown in Fig. 1 (curve 1) is very similar to the absorption spectmm of an Alq3 film deposited on NaCl (curve 2) and the bulk Alq3. A shift of the maximum of the spectral band by 1-3 cm observed for the Alq3 films on the Au precoat can be caused by an influence of the substrate local fields. 

The second method, developed by AUara et al. [42, 48, 49], relies on calculation of the theoretical reflection absorption spectrum for the same angle of incidence and the thin-cavity thickness as the values used during the collection of the experimental data. The optical constants of the window, electrolyte, and metal can be taken from the literature [22, 37-39], while the isotropic optical con-... 

In SNIFTIRS, the electrode potential is modulated between the base value (Ei) and the sample value E2), and the spectra of the reflected infrared radiation are measured. The reflection absorption spectrum (AR/R) is obtained by plotting... 

In PM IRRAS, the incident beam polarization is modulated between two orthogonal directions (a) perpendicular (s-polarization) and (b) parallel (p-polar-ization) to the plane of incidence of the infrared beam. At the metal surface, the electric field of the s-polarized infrared beam almost vanishes, while the electric field of the p-polarized beam is enhanced (see Fig. 9.3). Thus, the first component of the modulated signal is insensitive to the presence of the film of adsorbed molecules and can be used to obtain the background spectrum, while the other component can be utilized to obtain the spectrum of the film. Modulation between s- and p-polarizations is carried out at a high frequency (50 kHz), and the reflection absorption spectrum AR/(R) is obtained as... 

The polarization modulation reflection absorption spectrum acquired using the SSD can therefore be written as... 

Place working sample into the path of the beam and collect transmission/ reflectance/absorption spectrum... 

The in situ reflection-absorption spectrum of nitrate ions on a Au(lOO) electrode is shown in Fig. 9, in which two bands at 1436 and 1024 cm can be observed. The 1436 cm band has been assigned to the Ai symmetric mode for the nitrate ions... 

Figure 5.13 (A) Reflection/absorption spectrum and (B) visual image of a HeLa cell...

The UV diffuse reflectance absorption spectrum of lanthanum indate, LalnOs, showed threshold absorption wavelength at 480 nm, main absorption in the wavelength region 450 to 350 nm, and the highest level at 280 nm [20]. RUO2-dispersed LalnOa had the photocatalytic activity under Hg-Xe lamp irradiation. 

The first commercially successful off-line DD-HPLC/FT-IR interface was the LC Transform, made by Lab Connections [41]. With this device, nebulization is initiated ultrasonicaUy and the solvent is evaporated with either a thermospray or a concentric flow nebulizer. The solutes are first deposited on a rotating germanium disk on the underside of which a thick layer of aluminum has been deposited. After the deposition step, the disk is then moved to a specular reflection accessory that is mounted in the sample compartment of a standard FT-IR spectrometer. The developers of the LC Transform recognized that it is more convenient to measure the spectra of the components that had been deposited on the disk by reflection spectrometry than by transmission. However, the deposition of a very thin film of each eluate on a metal substrate would not allow its reflection-absorption spectrum to be measured with adequate efficiency without resorting to grazing incidence measurements, for which the disadvantages were discussed in Section 23.3.3. 

The intensity of a reflection-absorption spectrum is expressed by A/ // q (called the absorption factor by Greenler [1]), or more frequently by the reflection-absorbance ... 

Figure 10.9 Reflection-absorbance spectrum of fluorocarbon lubricant applied to the surface of a magnetic disk, (a) Reflection-absorbance spectrum of a magnetic disk without the fluorocarbon on it (b) reflection-absorption spectrum of the same disk with the fluorocarbon on it, and (c) a difference generated by subtracting spectrum (a) from spectrum (b). The ordinate scale in (c) has been expanded eight times.

The three spectra shown in Figure 10.9 are (a) the reflection-absorption spectrum of a magnetic disk without fluorocarbon lubricant applied, (b) that with fluorocarbon lubricant, and (c) a difference spectrum between the spectra in (b) and (a). Spectrum (a) shows absorption bands due to polymer components present in the magnetic material on an aluminum... 

The infrared reflection/absorption spectrum of the coatings was obtained using a Perkin-Elmer FT-IR Spectrum 100 spectrometer. The coating spectrum was ratioed against the spectrum of the substrate background. A pure fluoro-organic compound spectrum was obtained on insertion in the KBr pellets in the transmittance mode. 

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