Absorption bands of water

Fig. 30. Upper Combination band v + v2 of water. Lower Absorption band of water in collagen during drying142 . The most dried sample 3 shows a A similar to supercooled water at - 20 °C...

This is how to cope with any interference caused by the presence of atmospheric water vapor and carbon dioxide. Air samples are irradiated by light at two different wavelengths, one, which corresponds to a strong absorption band of water vapor and the other of carbon dioxide. From these measurements it is possible to compensate each measurement for interference from these two gases. It is of major importance that the water vapor interference compensation is accurate, which is ensured by a thorough calibration procedure. 

An increase in global C02 concentration of only 1% (or about 3 ppm) has significant consequences on the weather. The instruments used to measure atmospheric COz concentrations must be highly precise. With NDIR detectors, because the absorption bands of water and C02 somewhat overlap, a freeze-out trap (-80°C or -112°F) is used in the sample preparation system to remove water prior to the measurement. 

The resulting continuum is very broad, since it could be measured from 230 nm in the ultraviolet to 4.5 pm in the mid-infrared. The combined spectrum is shown in Fig. 15.8. The fast decrease of the spectrum up to 2.5 pm (4 orders of magnitude between 800 nm and 2.5 pm) slows down beyond 2.5 pm, with only one order of magnitude drop between 2.5 and 4.5 pm. On the spectrum, the absorption band of water between 1.8 and 2.5 pm is clearly visible, showing the potential of the white-light for optical remote sensing in the atmosphere. 

The thickness of the membrane should exceed the penetration depth of the IR radiation in order to suppress the absorption bands of water. The optimum thickness is about 10 to 20 pm. The stability of such a membrane is satisfactory and the resulting time constant for the enrichment process is not too large. 

A long-term treatment of PS in a weak magnetic field also contributes to a short-wave shift of the OH stretching band (Fig. 2). In our recent work [5], it was found that the position of the valence absorption bands of water in PS silicon varies between 2900 and 3550 cm", which was concerned with variation of the energy of hydrogen bonds and water states in PS. This shift of the OH absorption... 

The absorption bands of water vapor and carbon dioxide are always present in the infrared spectrum of the expired breath because both these substances strongly absorb infrared radiation. On the other hand, oxygen, nitrogen, and the inert gases do not absorb infrared radiation and therefore cannot be detected— an advantage for the methods to be discussed. 

Ataka and co-workers [171] have presented the following interpretation of the absorption bands of water in the ATR-SEIRA spectra of the Au 0.5 M HCIO4 interface measured in the DL region from - -0.1 to -1-1.3 V (SHE) (Fig. 3.41). 

The position of the absorption bands of water in the hydration spheres depends on the origin of the ions [200] (Table 3.4, Part A). Certain correlations were also observed between ability of adsorbed ions to structure the water of hydration and IR spectra of interfacial water (Table 3.4, Part B). For a series of aqueous... 

Figure 14.28 Normalized integral of absorption band of water and pad-related band versus...

In 1968, Sinsheimer and Keuhnelian used the 1900 nm absorption band of water to quantify water with the same accuracy as Karl Fischer titration [5]. This is a combination band of fundamental stretching and... 

Water incorporated into fused silica is of considerable importance because the resulting silanol groups affect the NIR transmission of silica optical fibers and other optical components. Silanols are discussed in the OH section. In mixed glasses, such as those containing borosilicates, aluminosilicates, and so on, associated water OH groups give rise to diffuse absorption bands. The absorption bands of water molecules on silica surfaces have been described by Klier et al. " ... 

Another problem is the very broad and intensive absorption bands of water that overlap the absorption bands of protein and fat in the NIR milk spectrum for a great part (Figure 20.1). This overlap makes it difficult to correlate specific bands to the constituents from which they arise. Besides, the small variation of protein and fat content in standardized milk may cause only very slight changes in the NIR spectrum. Therefore, it is necessary to transform the raw data to first and second derivatives to interpret and correlate the overlapping absorption bands of protein and fat in... 

Raman spectroscopy uses an incident laser beam that is focused on the sample. The intensity of the scattered light is measured as a function of its frequency. Bands appear in the spectrum that are shifted in frequency from the frequency of the incident light. Each shift in frequency corresponds to one of the vibrational frequencies of the molecule. Infrared spectroscopy measures the absorption of infrared light as a function of its frequency. Absorption bands appear in the spectrum that correspond to vibrational frequencies in the DNA. Infrared spectroscopy is hindered by the strong almost continuous absorption band of water while Raman spectroscopy benefits from the fact that water is a weak Raman scatterer. Infrared spectroscopy is of greater usefulness in the studies of films and fibers while Raman is of use in obtaining the vibrational frequencies of DNA in crystals, films, fibers, and aqueous solutions. A large amount of evidence, both theoretical and experimental, now exists which shows that there is a close relation between the conformation of a DNA and the frequencies and the intensities of certain bands in the Raman spectra. The theory for the relation between the frequencies and intensities and the DNA conformation is outlined in the next two sections. 

The presence of mantles on silicate grains is revealed by absorption bands of water ice, superimposed with features from carbon monoxide, carbon dioxide, methanol and other less abundant constituents. As for the silicate bands, the spectral features associated with molecular ices are most prominent in the infrared spectral region, between 3 and 40 pm mainly. Because water ice is the main constituent of ice mantles, the spectral features due to water ice are the strongest, especially the 3.1 pm feature due to the stretching mode of the 0-H bound in solid water. This band can be fully saturated for deeply embedded young stellar objects. 

Figure 8.11. Expanded plot of the spectra shown in Figure 8.10, showing apparent spectral artifacts in the region where the spectral intensity should be zero. The artifact at about 1500 cm has a similar structure to the absorption band of water at 7000cm and somehow results from folding, possibly because the interferogram was sampled at every zero crossing when the HeNe interferogram was not exactly centered at zero.

Higashi and coworkers designed and constructed an ATR-based FUV spectrometer [15]. In this spectrometer the design of a small intern reflection element (IRE) probe has led to successful measurement of the entire A<- X transition absorption band of water and aqueous solutions. 

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