Vibrational spectroscopy specular reflectance

Many types of spectroscopy have been coupled with electrochemistry including electronic absorption spectroscopy, X ray (see X-Ray Absorption Spectroscopy), infrared (IR) (see Vibrational Spectroscopy), or Raman spectroscopy, eUipsometry, specular reflectance, and electron spin resonance (ESR). Electronic absorption spectroscopy, one of the most prominent electrochemistry coupled with spectro-electrochemical techniques, will be discussed here as will... 

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... 

Figure Bl.25.12. Excitation mechanisms in electron energy loss spectroscopy for a simple adsorbate system Dipole scattering excites only the vibration perpendicular to the surface (v ) in which a dipole moment nonnal to the surface changes the electron wave is reflected by the surface into the specular direction. Impact scattering excites also the bending mode v- in which the atom moves parallel to the surface electrons are scattered over a wide range of angles. The EELS spectra show the higlily intense elastic peak and the relatively weak loss peaks. Off-specular loss peaks are in general one to two orders of magnitude weaker than specular loss peaks.

Thus infrared spectroscopy must be used in the reflectance mode in order to be surface sensitive. If infrared radiation is reflected specularly from an extremely good reflector on which there is an adsorbed layer, then the reflected light will show intensity losses at those frequencies that match vibrational frequencies at the surface. Such frequencies might be characteristic of the molecular structure within the adsorbed layer, modified or otherwise as a result of attachment to the surface, or of the molecule-surface system itself. Should the... 

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