Absorption spectra, characteristic shapes

In this paper we analyze the absorption spectrum characteristics (optical thickness, absorption line width and shape) in a self-similarly expanding gaseous sphere. 

It should be mentioned that medium effects do not usually change the characteristic shape of an absorption spectrum to such an extent that it can not be recognized. Thus the characteristic Bactrian camel shape of the absorption band of solutions of trityl chloride in sulfuric acid and in nitromethane leaves no doubt that essentially the same ion is present in both solvents. 

The absorption characteristics of PS I were measured on the four kinds of subphase surfaces during compression. As an example, Figure 2 shows the absorption spectra of the PS I monolayers on the PBV subphase surface under different surface pressures. Two absorption bands at about 420-450 and 676 nm increase with the compression, indicating the accumulation of the PS I to form a condensed monolayer. Compared to the absorption spectrum of PS I in solution (Fig. 3), the band at around 436 nm splits into two peaks. The wave-shaped small band between 470 and 630 nm is due to a low single-to-noise ratio on the water surface. These spectral features together with the jt-A isotherms indicate that PS I remains at the interface, and that the loss of PS I, due to dissolving into the subphase, is not significant [2],... 

The changes in the energy levels of these electrons owing to the absorption of radiation quanta give rise to characteristic bands in the absorption spectrum. The more easily the bond electrons in a molecule are excited, the more intense is the colour of the compound. The shape of the spectrum and the intensity of the absorption band depend on the position of the... 

The strong absorption at 1715 cm that corresponds to the carbonyl group (C=0) is quite intense. In addition to the characteristic position of absorption, the shape and intensity of this peak are also unique to the C=0 bond. This is true for almost every type of absorption peak both shape and intensity characteristics can be described, and these characteristics often enable the chemist to distinguish the peak in potentially confusing situations. For instance, to some extent C=0 and C=C bonds absorb in the same region of the infrared spectrum ... 

Figure 7.19 shows the ultraviolet spectra of naphthalene and anthracene. Notice the characteristic shape and fine structure of each spectrum, as well as the effect of increased conjugation on the positions of the absorption maxima. 

This section includes identification and measurement of carotenoids by UV/visible spectrophotometry and column chromatography. The UV/visible absorption and the chromatographic behavior spectrum provide the first clues for the identification of carotenoids. Both the wavelengths of maximum absorption (Xroax) the shape of the spectrum (spectral fine structures) are characteristics of the conjugated unsaturated part of the carotenoid molecule cmitaining delocalized 7t-electrons called the chromophore. The values of the carotenoids commonly found in natural products in various solvents are listed in Table 111.2. 

This method is based in the light-absorbing chromospheres and the visible absorption spectrum. The wavelength of maximum absorption (A,max) and the shape of the spectrum (spectral fine structure) are specific characteristics of each chromophore structure. In the past, most data on the amount of carotenoids found in foods were based on the total absorbance at a specified wavelength (450 nm). In some cases, a separation in an OCC was previously made followed by a spectroscopy. 

The peculiar spectral properties of CRBP-bound retinol and RME are indicative of specific ligand-protein interactions (see Fig. 2) Instead, other holo-retinoid-binding proteins exhibit less characteristic spectra. For example the absorption spectrum of the complex of retinol with plasma retinol-binding protein (RBP) is characterized by a single, well-shaped peak centered at approx 328 nm On the other hand, the absorption spectra of some CRBP-bound retinoids, like CRBP-bound a l-trans retinal (12,13), do not resemble those of CRBP-bound retinol and RME. 

As is clear in the above example, the reflection spectrum has bands having derivative shapes which are not observed in normal transmission spectra. This is characteristic of near-normal incidence external reflection spectra because they are greatly influenced by the real part (n) of the complex refractive index n = n + ik) (see Section 1.2.4) [1]. To derive an absorption spectrum from a reflectance spectrum, the procedure of analysis described in the next section should be followed. 

The above method for calculating 8 v) was applied to the R v) spectrum in Figure 8.4c. Then, the n(v) and k v) spectra were calculated by the use of Equations (8.4a) and (8.4b), and the results obtained are shown in Figure 8.5. The k(v) spectrum has the shape of an absorption spectrum, from which band positions can be accurately determined. The bands observed at 2919 and 2850 cm are, respectively, due to the CH2 antisymmetric and symmetric stretching vibrations characteristic of the all-trans planar zigzag conformation of the -alkane chain. The doublet bands at 1471 and 1462 cm are assigned to the CH2... 

Infrared emission from a material contains information characteristic of the material, and the information is obtainable in a form that is basically equivalent to an infrared absorption spectrum. Depending on the purpose of analysis and the shape of the target of analysis, infrared emission spectroscopy measurements can be more informative or convenient than an infrared transmission or reflection spectroscopy measurement, which is described elsewhere in this book. Infrared emission spectroscopy provides a means for the remote detection and analysis of gases, for example, volcanic gas and flue gases [1]. 

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