Surface-enhanced infrared absorbance

In contrast to Raman scattering, the absorption of infrared (IR) radiation is a first-order process, and in principle a surface or an interface can generate a sufficiently strong signal to yield good IR spectra [6]. However, most solvents, in particular water, absorb strongly in the infrared. There is no special surface enhancement effect, and the signal from the interface must be separated from that of the bulk of the solution. 

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. 

Sajanlal PR, Pradeep T (2009) Mesoflowers a new class of highly efficient surface-enhanced Raman active and infrared-absorbing materials. Nano Res 2(4) 306—320... 

The answer to the first question is easy there is a so-called surface selection rule such that only vibrations with a dipole perpendicular to the metal surface are infrared active. This is because a dipole moment change in an absorbed molecule induces an opposed dipole in the metal. This opposition leads to a zero nett dipole for dipoles parallel to the metal surface but an enhanced dipole perpendicular. (See the diagram). 

Coping with the greenhouse effect is a vei-y difficult sociopolitical problem. A greenhouse effect existed on Earth long before the Industrial Revolution. Had it not. Earth s surface would be much colder than it is now. The introduction of gases absorbing infrared radiation only enhances the greenhouse effect. Carbon dioxide is not the only gas of importance water vapor and methane, for exam-... 

NIR spectra are acquired using dried tissue, either whole or ground. The reflectance is measured relative to a so-called white reference, which is a highly reflective surface, such as Gore-Tex or white ceramic. Near-infrared reflectance spectra, or absorbance spectra, defined as log(l/R), with R being the reflectance, look rather flat. For analysis purposes the second derivative of the spectra is often used, because it enhances certain spectral features. 

High enhancement of the copper localized surface plasmon absorbency was recorded at the two-layer planar system consisted of copper and silver nanoparticles prepared with successive vacuum evaporation. The result obtained may be caused by strong near-field coupling in the close-packed binary system. The effect may be used for the development of high-absorptive coatings and spectral selective nanoelements in the visible and near infrared spectral ranges. 

Zeolites. The weak Raman signals arising from the aluminosilicate zeolite framework allow for the detection of vibrational bands of adsorbates, especially below 1200 cm which are not readily accessible to infrared absorption techniques. Raman spectroscopy is an extremely effective characterization method when two or more colored species coexist on the surface, since the spectrum of one of the species may be enhanced selectively by a careful choice of the exciting line. A wide range of adsorbate/zeolite systems have been examined by Raman spectroscopy and include SO2, NO2, acety-lene/polyacetylene, dimethylacetylene, benzene, pyridine, pyrazine, cyclopropane, and halogens. Extensive discussions of these absorbate/zeolite studies are found in a review article by Bartlett and Cooney. ... 

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