Infrared water bands

The presence of water can affect physical properties such as viscosity, but we mention it in this section because of its important optical effects in particular, it produces strong absorption bands in the near-infrared spectral region. Avoidance of the absorption bands due to water in silica is one of the key reasons the wavelength locations of the two current long-distance optical communications wavelength bands, at 1.31 and 1.55 /an, were chosen. For other glasses, measurement of the intensities of the near-infrared water bands allows a quantitative determination of the amount of water in the glass i.e., it provides an analytical technique. 

Wirzing 216a, 216b) found that the combination bands in the near infrared were particularly well-suited for the distinction of silanol groups and water. Bands were observed at 4545-4365 cm and at... 

S.2.2.2 ICLS Example 2 This example discusses the determination of sodium hydroxide (caustic) concentration in an aqueous sample containing sodium hydroxide and a salt using NIR spearoscopy. An example of this problem in a chemical process occurs in process scrubbers where CO, is converted to Na,CO and H,S is converted to Na,S in the presence of caustic. Although caustic and salts have no distinct bands in the NIR, it has been demonstrated that they perturb the shape of the water bands (Watson and Baughman, 1984 Phelan et al., 1989)-Near-infrared spectroscopy is therefore a viable measurement technique. This method also has ad tages as an analytical technique for process analysis because of the stability of the instrumentation and the ability to use fiber-optic probes to multiplex tlie interferometers and Icx ate them rcm< >tely from the processes. 

There may, however, be some cancellation of errors. For example, the concentration of atmospheric C02 ([ref], in Eq. (T)) depends in a nonlinear fashion on the amount of total dissolved inorganic carbon in the ocean surface layer because of the equilibria with water (see Chapter 8.B) so that relatively less atmospheric C02 can be taken up by the oceans as its atmospheric concentrations increase. This would leave relatively more C02 in the atmosphere, increasing its greenhouse effect. On the other hand, since the strongest infrared absorption bands of C02 are already saturated (vide supra), the radiative forcing (at-(), in Eq. (T)) decreases as its concentrations increase. 

It is not possible to dissolve the asphaltenes in water by treatment of the halo derivatives with aqueous sodium hydroxide or with aqueous sodium sulfite (II). The hydrolyzed products remained insoluble even in a strongly alkaline solution. The decreased (H + Cl)/C ratios and the increased O/C ratios of the products relative to those of the parent halo-asphaltenes indicate that partial reaction occurs. The infrared spectra of the products showed a broad band centered at 3450 cm 1, a region assigned to the presence of hydroxyl groups in the products, but it was not possible to establish conclusively the presence of sulfonic acid group(s) in the product from the sodium sulfite reaction by assignment of infrared absorption bands to this particular group. 

In water, at ordinary concentrations, the hydrogen chloride is practically all present as the hydrated ions. The infrared absorption bands characteristic of HCl, and shown by the liquid hydride and its solutions in nonionizing solvents do not appear in the aqueous solutions.451 In dilute solutions, the conductivities agree with the Debye-Huckel-Onsager formula. 

The vibrational spectrum of H+ is even harder to interpret. Absorption increases at all frequencies in the infrared and the already broad water bands get broader, but not symmetrically. The additions to the water bands have been interpreted as the new bands of the HsO+ unit in H+ (Falk and Gigufere, 1957). The suggested frequencies are shown in Table 9. On the other hand it has been suggested that the rapid proton shifts from one oxygen to another precludes a band spectrum for that unit in water (Ackermann, 1961) and its absorption has been... 

As expected for silica-alumina as a mixed oxide (see also Section IV.B.5), the PyH+ and PyL species are observed simultaneously (160, 205,206,221-223). Two distinct types of Lewis acid sites could be detected (19b mode at 1456 and 1462 cm-1, respectively) on a specially prepared aluminum-on-silica catalyst (160). On water addition, the Lewis sites can be converted into Br nsted sites (160, 205, 221), The effect of Na+ ions on the acidity of silica-aluminas has been studied by Parry (205) and by Bourne et al. (160). It can be concluded from Parry s results that Na+ ions affect both types of acid sites, so that alkali poisoning does not seem to eliminate the Br nsted sites selectively. For quantitative determination of the surface density of Lewis and Br nsted acid sites by pyridine chemisorption, one requires the knowledge of at least the ratio of the extinction coefficients for characteristic infrared absorption bands of the PyH+ and PyL species. Attempts have been made to evaluate this ratio for the 19b mode, which occurs near 1450 cm-1 for the PyL species and near 1545 cm-1 for the PyH+ species (160,198,206,221,224,225). The most reliable value as calculated from the data given by Hughes and White (198) seems to be... 

Dibromodimethylplatinum(IV) is a yellow crystalline solid that decomposes at 180-190°. It is insoluble in water and sparingly soluble in organic solvents. Although no X-ray crystal structure data are available, the complex is expected to be polymeric if the usual six-coordination of platinum(IV) is maintained. In methanol solution it is monomeric. Its reactivity with a variety of ligands has been described.7 Sharp infrared absorption bands at 1220 (s), 1222 (w, sh), 1245 (w), and 1252 (m) cm-1 in the CH3 deformation region are characteristic of the compound. 

The compound exists as a red powder that is moderately stable in air, but it should be stored under nitrogen if it is to be kept for prolonged periods. The crystals take the shape of dark-red needles and are moderately stable in air. The compound is soluble in organic solvents but insoluble in water. The structure has been determined by single crystal X-ray diffraction (see Fig. 1, )2b Infrared spectral bands in the carbonyl region appear at 1959.0 (w), 1964.8 (m), 1979.5 (s),... 

Ammonium cyanate is a white solid, which rearranges to urea upon prolonged storage or heating. It is extremely soluble in water, slightly soluble in acetonitrile, ethanol, and chloroform, and insoluble in benzene and diethyl ether. The infrared spectrum and x-ray diffraction powder pattern are most useful for determining the absence of urea in the final product. Nujol mulls of pure ammonium cyanate exhibit absorptions at 3160 (s), 2190 (s), 1334 (m), 1243 (m), and 640 (m) cm-i and are free of any infrared-active bands in the regions characteristic of urea, that is, 3456 and 1683 cm-i. 

The 3-/im infrared absorption band in wet synthetic quartz is due to high-pressure clusters of molecular water rather than point defects (Aines and Rossman 1984 Gerretsen et al. 1989). 

Recent infrared spectra of the shifted suppressed water bands indicate that the surface of Europa contains hydrated minerals. These have been suggested to be hydrated salts and organics, which would also be consistent with material from an underground ocean. Because of this strong, but indirect, evidence for an ocean, Europa is now considered to be an object on which biological materials could have evolved. Such an evolution, if it occurred, could have been driven by the heat created by the tidal interaction with Jupiter, although recently this has been suggested to be too small. 

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