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Infrared interaction with molecules

Interaction of infrared radiation with molecules and crystals to produce absorption (or reflectance) bands can be predicted using group theory (see Orchin and Jaffe, 1971 Cotton, 1971), and the same approach is used in the prediction and interpretation of other vibrational spectra (such as Raman spectra). [Pg.55]

Another approach to acquire infrared spectra of the electrochemical interface takes advantage of the so-called surface selection mle, which states that only p-polarized light may interact with molecules at a metal electrode while s-polarized may not. P-polarized light is light in which the electrical field vector is parallel to the plane formed by the incident and the reflected beam, while s-polarized fight is perpendicular to the plane of incidence. Furthermore, only molecules having a dipole perpendicular to the surface may interact with p-polarized fight [5]. [Pg.1073]

Infrared external reflection spectroscopy is used extensively in the study of thin films on metallic substrates, the incident beam is directly reflected from the metallic surface, and the transmitted beam is attenuated in the regions of substrate absorption for other materials. The reflected beam interacts with molecules situated at the surface of partially transmitting materials. The resulting reflectance spectra are functions of polarization and incidence angle of the incident beam and provide a quantitative measure of the surface concentrations and an indirect measure of the structure and orientation of molecules in the surface layer. [Pg.95]

Infrared, ultraviolet, and nuclear magnetic resonance spectroscopies differ from mass spectrometry in that they are nondestructive and involve the interaction of molecules with electromagnetic energy rather than with an ionizing source. Before beginning a study of these techniques, however, let s briefly review the nature of radiant energy and the electromagnetic spectrum. [Pg.418]

The basic methods of the identification and study of matrix-isolated intermediates are infrared (IR), ultraviolet-visible (UV-vis), Raman and electron spin resonance (esr) spectroscopy. The most widely used is IR spectroscopy, which has some significant advantages. One of them is its high information content, and the other lies in the absence of overlapping bands in matrix IR spectra because the peaks are very narrow (about 1 cm ), due to the low temperature and the absence of rotation and interaction between molecules in the matrix. This fact allows the identification of practically all the compounds present, even in multicomponent reaetion mixtures, and the determination of vibrational frequencies of molecules with high accuracy (up to 0.01 cm when Fourier transform infrared spectrometers are used). [Pg.6]

When infrared beam incidents upon thin organic films extended over a plain metal surface (Figure 1), there usually occurs a standing wave electric field on the metal surface as a consequence of the interference between the incident and reflected beams. Since the standing wave may interact with, i. e. be absorbed by, molecules in the organic film, the reflectance of the beam from the metal surface is reduced. [Pg.157]


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