Reflection adsorbed species vibrations

While s-polarized radiation approaches a phase change near 180° on reflection, the change in phase of the p-polarized light depends strongly on the angle of incidence [20]. Therefore, near the metal surface (in the order of the wavelength of IR) the s-polarized radiation is greatly diminished in intensity and the p-polarized is not [9]. This surface selection rule of metal surfaces results in an IR activity of adsorbed species only if Sfi/Sq 0 (/i = dipole moment, q = normal coordinate) for the vibrational mode perpendicular to the surface. 

Another very important consequence due to the reflection rale described here is that only those fundamental vibrations of adsorbed species which have a finite value of the dipole derivative perpendicular to the surface can undergo interaction with the radiation. Consider a simple case of a diatomic molecule adsorbed on the surface (Fig. 6.25). When this molecule lies on the surface, its dipole moment is parallel to the... 

One of the major advances in the past decade has been the maturation of the electronic revolution. This has had its effect on surface spectroscopy, with regard to instrumentation for transmission IR, but particularly for sensitivity gains that have made reflectance techniques the preferred alternative for fundamental studies. In the transmission mode, the commercial development of the Fourier transform IR spectrometer has led to significant advantages in the determination of the vibrational spectra of adsorbed species. This is covered in the chapter by Bell. 

Changes in the vibrational modes of the adsorbent, however, reflect only those changes which occur to the substrate they do not provide direct insight into the structure and bonding of the adsorbed species. In order to examine the influence of the surface on the intercalated species, the vibrational modes of the adsorbate must be obtained. In a previous dispersive-IR absorption study of the kaolinite-hydrazine intercalate, Ledoux and White (17) observed that the ISu hydroxyl groups of... 

The development of infrared reflection-absorption spectroscopy to study gas-phase/solid interface started as a necessary step to avoid the practical limitations imposed by the use of oxide-supported metals [20]. This improvement opened the possibility of studying adsorbed species on well-defined metal surfaces, from which a considerable knowledge of the vibrational properties at the gas-phase/metal interface has been gained [21]. This information from ultrahigh vacuum (UHV) systems provides the basis for the application of the infrared technique to studying the (more complex) electrochemical interface. 

In situ FTIR reflection spectra of a PAn I PB I Pt electrode are shown in Fig. 2 where the potential was stepped from 0 V vs Ag I AgCI to the cathodic side. The downward and upward bands correspond to the increase and decrease in concentration of adsorbed species on the electrode, respectively. The band observed at the wavenumber of 3600 to 3200 cm is attributable to the vibrational absorption of HjO. The negative-going peak at 2100 cm, which increases with stepping the potential to less noble side, means the electroreduction of PB to its reduced form (ES). A broad band appearing in the wavenumber region higher than 1600 cm is ascribed to the electronic absorption of PAn that is caused by free carriers (unpaired... 

Klier K (1980) Investigations of adsorption centers, molecules, surface complexes, and interactions among catalyst components by diffuse reflectance spectroscopy. In Bell AT, Hair ML (eds) Vibrational spectroscopies for adsorbed species. ACS Symp Ser 137 141. American Chemical Society, Washington... 

Specular reflection spectroscopy has been actively used in in situ studies of the formation and optical behaviour of monolayer films on surfaces, and for detecting intermediates and products of heterogeneous chemical and electrochemical reactions. The vibrational spectra of the adsorbed species at electrode surfaces are obtained by surface-enhanced Raman scattering and infrared reflectance spectroscopies. Since the mid-1960s, modulated reflection spectroscopy techniques have been employed in elucidating the optical properties and band structure of solids. In the semiconductor electroreflectance, the reflectance change at the semiconductor surface caused by the perturbation of the dielectric properties of... 

Reflection - Absorption Infrared Spectroscopy. In RAIRS, IR radiation is reflected from a plane surface through an adsorbed layer, the reflected light losing intensity at those frequencies at which the light frequency coincides with a vibrational mode at the surface. The vibrations may be those within the adsorbed species itself, or they may arise from interaction with surface atoms. 

High-resolution electron energy loss spectroscopy HREELS Vibrational excitation of surface atoms by inelastic reflection of low energy electrons Structure and bonding of surface atoms and adsorbed species... 

Besides infrared reflection spectroscopy, Raman spectroscopy, particularly surface-enhanced Raman spectroscopy (SERS), is able to provide information about the structure of the electrode/electrolyte interface through the identification of adsorbed species from their vibrational spectra/ However, Raman spectroscopy is not of as general use as infrared spectroscopy, and the basis of the enhancement mechanism, which is observed only for a limited number of systems (e.g., adsorption of pyridine on a silver electrode), is not yet very clear/ Surface-enhanced Raman scattering is discussed by Birke and Lombardi in Chapter 6 of this book. 

Raman spectroscopy has provided information on catalytically active transition metal oxide species (e. g. V, Nb, Cr, Mo, W, and Re) present on the surface of different oxide supports (e.g. alumina, titania, zirconia, niobia, and silica). The structures of the surface metal oxide species were reflected in the terminal M=0 and bridging M-O-M vibrations. The location of the surface metal oxide species on the oxide supports was determined by monitoring the specific surface hydroxyls of the support that were being titrated. The surface coverage of the metal oxide species on the oxide supports could be quantitatively obtained, because at monolayer coverage all the reactive surface hydroxyls were titrated and additional metal oxide resulted in the formation of crystalline metal oxide particles. The nature of surface Lewis and Bronsted acid sites in supported metal oxide catalysts has been determined by adsorbing probe mole-... 

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