Infrared radiation absorption

For any molecular vibration that leads to infrared absorption, there is a periodic change in electric dipole moment. In case the direction of this change is parallel to component of the electric vector of the infrared radiation, absorption takes place otherwise it does not. In oriented bulk polymers, the dipole-moment change can be confined to specified directions. The use of polarised infrared radiation in such a case leads to absorption which is a function of the orientation of the plane of polarisation. The... 

The two preceding methods have been combined to determine the tritium isotope effect. In a tritium-labeled substrate in D20, the change in infrared radiation absorption arises almost entirely from release of protons because the concentration of the tritium species in the reactant is small. Thus, the rate constant kH (determined by the change in the DOH absorption) represents release of protons. The constant kT for release of tritium to the solvent is determined from radioactivity measurements of water from the same reaction mixture. In the enolization of... 

A spectroscopic technique in which a compound is irradiated with infrared radiation, absorption of which causes covalent bonds to change from a lower vibration state to a higher one. Infrared spectroscopy is particularly valuable for determining the kinds of functional groups present in a molecule. 

Recently, a series of chemical substances called functional dyes have attracted considerable attention. Because such dyes have long conjugated pi-electron systems and in many cases possess intramolecular charge transfer structures, functional dyes are expected to show interesting optical and electronic properties. Among functional dyes, phthalocyanine compounds have been extensively investigated because of their excellent physical, chemical and coloristic properties, as mentioned above. For example, about 1000 related US patents, published from 1990 onwards, are retrievable from the World Patent Index data base of Derwent, and more than 30 % of these are classified in such non-colorant applications as electrophotography, catalysis, and infrared radiation absorption. 

Interpretation of the results requires a knowledge of the orientation of the water molecules on the platinum surface and the mechanism of infrared radiation absorption. 

He Y, Pochert J, Quack M, Ranz R and Seyfang G 1995 Dynamics of unimolecular reactions induced by monochromatic infrared radiation experiment and theory for C F XI—> C F X + I probed with hyperfine-, Doppler- and uncertainty limited time resolution of iodine atom infrared absorption J. Chem. Soc. Faraday Discuss. 102 275-300... 

Thermal Transducers Infrared radiation generally does not have sufficient energy to produce a measurable current when using a photon transducer. A thermal transducer, therefore, is used for infrared spectroscopy. The absorption of infrared photons by a thermal transducer increases its temperature, changing one or more of its characteristic properties. The pneumatic transducer, for example. 

In absorption spectroscopy a beam of electromagnetic radiation passes through a sample. Much of the radiation is transmitted without a loss in intensity. At selected frequencies, however, the radiation s intensity is attenuated. This process of attenuation is called absorption. Two general requirements must be met if an analyte is to absorb electromagnetic radiation. The first requirement is that there must be a mechanism by which the radiation s electric field or magnetic field interacts with the analyte. For ultraviolet and visible radiation, this interaction involves the electronic energy of valence electrons. A chemical bond s vibrational energy is altered by the absorbance of infrared radiation. A more detailed treatment of this interaction, and its importance in deter-... 

Energy level diagram showing difference between the absorption of Infrared radiation (left) and ultravlolet-visible radiation (right). 

Infrared instruments using a monochromator for wavelength selection are constructed using double-beam optics similar to that shown in Figure 10.26. Doublebeam optics are preferred over single-beam optics because the sources and detectors for infrared radiation are less stable than that for UV/Vis radiation. In addition, it is easier to correct for the absorption of infrared radiation by atmospheric CO2 and 1420 vapor when using double-beam optics. Resolutions of 1-3 cm are typical for most instruments. 

In the process of absorption or emission of infrared radiation involving transitions between two vibrational states the interaction is usually between the molecule and the electric, rather than the magnetic, component of the electromagnetic radiation (see Section 2.1). For this... 

Infrared Spectra of Ionomers. Infrared absorption data, first pubHshed in 1964 (11), show that partial neutralization of ethylene—methacryhc acid introduced new absorption bands at 1480 1670 cm for the ionized carboxylate group while the 1698 — cm band of the free acid carboxyl diminishes in size (21). In addition to providing information on stmctural features, the numerous absorption bands ate significant in apphcations technology, providing rapid warmup of film and sheet under infrared radiation. 

Additions to the PLM include monochromatic filters or a monochromator to obtain dispersion data (eg, the variation in refractive index with wavelength). By the middle of the twentieth century, ultraviolet and infrared radiation were used to increase the identification parameters. In 1995 the FTIR microscope gives a view of the sample and an infrared absorption pattern on selected 100-p.m areas (about 2—5-ng samples) (37). 

The primary reference method used for measuring carbon monoxide in the United States is based on nondispersive infrared (NDIR) photometry (1, 2). The principle involved is the preferential absorption of infrared radiation by carbon monoxide. Figure 14-1 is a schematic representation of an NDIR analyzer. The analyzer has a hot filament source of infrared radiation, a chopper, a sample cell, reference cell, and a detector. The reference cell is filled with a non-infrared-absorbing gas, and the sample cell is continuously flushed with ambient air containing an unknown amount of CO. The detector cell is divided into two compartments by a flexible membrane, with each compartment filled with CO. Movement of the membrane causes a change in electrical capacitance in a control circuit whose signal is processed and fed to a recorder. 

As indicated above, the penetration depth is on the order of a micrometer. That means that in ATR, absorption of infrared radiation mostly occurs within a distance 8 of the surface and ATR is not as surface sensitive as some other surface analysis techniques. However, ATR, like all forms of infrared spectroscopy, is very sensitive to functional groups and is a powerful technique for characterizing the surface regions of polymers. 

A powerful characteristic of RAIR spectroscopy is that the technique can be used to determine the orientation of surface species. The reason for this is as follows. When parallel polarized infrared radiation is specularly reflected off of a substrate at a large angle of incidence, the incident and reflected waves combine to form a standing wave that has its electric field vector (E) perpendicular to the substrate surface. Since the intensity of an infrared absorption band is proportional to / ( M), where M is the transition moment , it can be seen that the intensity of a band is maximum when E and M are parallel (i.e., both perpendicular to the surface). / is a minimum when M is parallel to the surface (as stated above, E is always perpendicular to the surface in RAIR spectroscopy). 

There is limited application for CO trim systems which are widely used on utility and other large water-tube boilers. The principle of operation is for an infrared beam to traverse the flue from emitter to sensor. The absorption of the infrared radiation is proportional to the CO content. 

An example of an absorption spectrum—that of ethanol exposed to infrared radiation—is shown in Figure 12.12. The horizontal axis records the wavelength, and the vertical axis records the intensity of the various energy absorptions in percent transmittance. The baseline corresponding to 0% absorption (or 100% transmittance) runs along the top of the chart, so a downward spike means that energy absorption has occurred at that wavelength. 

Immersion heaters. An immersion heater consisting of a radiant heater encased in a silica sheath, is useful for the direct heating of most acids and other liquids (except hydrofluoric acid and concentrated caustic alkalis). Infrared radiation passes through the silica sheath with little absorption, so that a large proportion of heat is transferred to the liquid by radiation. The heater is almost unaffected by violent thermal shock due to the low coefficient of thermal expansion of the silica. 

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