Ordinary Infrared

The wave length 15p corresponds to wave number equal to 667 cm4. Thus in terms of wave number, the ordinary infrared region cover 4000 cm 1 to 667 cm 1. 

The amount of radiation used is also important. A Nernst glower is used in ordinary infrared spectroscopy. This light source emits a relatively low amount of radiation, and no destruction of the analyzed material occurs. However, Raman infrared spectroscopy employs a radiation source of much greater energy. This radiation is sufficiently energetic to cause bond disruption and some destruction of the analyzed material. 

The necessary instrumentation for making dichroic measurements depends on the technique used. The most common method is to use a single polarizer and an ordinary infrared or ultraviolet spectrophotometer. The sample (thin film) is then placed in the sample beam preferably before the polarizer and generally with the stretch axis at 45° to the entrance slit of the monochromator. This inclination of the stretch axis is to minimize the effect of machine polarization. Such effects have been discussed by Makus and Shareliff (42) and Jones (28). The electric vector of the polarizer is then aligned either parallel or... 

Fourier transform spectroscopy was first developed by astronomers in the early 1950s to study the infrared spectra of distant stars only by the Fourier technique could the very weak signals from these sources be isolated from environmental noise. The first chemical applications of Fourier transform spectroscopy, which were reported approximately a decade later, were to the energy-starved far-infrared region by the late 196Qs. instruments for chemical studies in both the far-infrared (10 to 400 cm ) and the ordinary infrared regions were available commercially. Descriptions of Fourier transform instruments for the ultraviolet and visible spectral regions can also be found in the literature, but their adoption has been less widc,spread. ... 

In ordinary infrared measurements, the requirements for the optical properties of cell windows and other materials (flatness, transparency, etc.) are not as severe as needed for ultraviolet and visible spectroscopy. Sometimes it is even necessary to make the window surface slightly coarse or to make its surfaces slightly deviated from parallel to avoid interference effects. However, such measures should never be taken in VCD measurements in order to ensure that circularly polarized radiation may be generated without fail. In VCD measurements, cell windows must be flat and parallel. A mirror cannot be used for any purpose. Samples should be transparent. VCD will not be observed in samples such as colloids because of scattering. 

The value of B is much smaller than v e, such that a much smaller amount of energy is required to rotate the molecule for a typical molecule, this lies within the microwave region. However, due to the vibrational energy of this molecule, the set of absorptions lie within the infrared region, allowing a spectrum showing the rovibrational modes of this molecule to be easily collected using an ordinary infrared spectrometer with a conventional gas cell. 

Optical Properties. Teflon FEP fluorocarbon film transmits more ultraviolet, visible light, and infrared radiation than ordinary window glass. The refractive index of FEP film is 1.341—1.347 (74). 

The PLM can be used in a reflection or a transmission mode. With either mode, light of various wavelengths from ultraviolet to infrared, polarized or unpolarized, is used to yield a wide variety of physical measurements. With just ordinary white light, a particle or any object detail down to about 0.5 p.m (500 nm) in diameter can be observed to detect shape, size, color, refractive index, melting point, and solubiUty in a group of solvents, all nondestmetively. Somewhat larger particles yield UV, visible, or IR absorption spectra. 

Figure 2.9 Spectra of a single adenine nanocrystal, (a) TERS spectrum, (b) ordinal SERS spectrum, and (c) ordinary near-infrared (NIR) Raman spectra. For the SERS measurement, a silver island film was used. For the NIR Raman measurement, i thick sample of adenine was used with a 1 h exposure.

At low pressure, the only interactions of the ion with its surroundings are through the exchange of photons with the surrounding walls. This is described by the three processes of absorption, induced emission, and spontaneous emission (whose rates are related by the Einstein coefficient equations). In the circumstances of interest here, the radiation illuminating the ions is the blackbody spectrum at the temperature of the surrounding walls, whose intensity and spectral distribution are given by the Planck blackbody formula. At ordinary temperatures, this is almost entirely infrared radiation, and near room temperature the most intense radiation is near 1000 cm". ... 

The second submove, describe instrumentation, describes the scientific apparatus used in the study. Both custom-built instruments (e.g., a high-vacuum chamber or a newly designed light source) and commercially available instruments (e.g., a gas chromatograph or an infrared spectrometer) are described. Ordinary lab equipment (e.g., a heating mantel or a rotary evaporator) is not described. 

PAS spectra are similar to those obtained using ordinary Fourier transform infrared (FTIR) spectroscopy except truncation of strong absorption bands which occurs due to photoacoustic signal saturation. PAS allows the structure to be studied at different thicknesses because the slower the frequency of modulation, the deeper the penetration of IR radiation. 

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