Spectrum of water

Fig. 2. Power spectrum of water dynamics with frequency in units of fs...

Figiue 7.12 from Guillot B 1991. A Molecular Dynamics Study of the Infrared Spectrum of Water. The Journal of Chemical Physics 95 1543-1551. 

Fig. 7.12 Experimental and calculated infrared spectra for liquid water. The black dots are the experimental values. The thick curve is the classical profile produced by the molecular dynamics simulation. The thin curve is obtained by applying quantum corrections. (Figure redrawn from Guilbt B 1991. A Molecular Dynamics Study of the Infrared Spectrum of Water. Journal of Chemical Physics 95 1543-1551.)...

The range of pore sizes in which TSK-GEL PW and TSK-GEL PWxi columns are available permits a wide spectrum of water-soluble substances to be analyzed. Calibration curves for polyethylene glycols chromatographed on... 

Another easy way of assembling a meaningless set of data is to work with a system for which you do not understand or control all of the important parameters. This would be easy to do, for example, when working with near infrared (NIR) spectra of an aqueous system. The NIR spectrum of water changes with changes in pH or temperature. If your measurements were made without regard to pH or temperature, the differences in the water spectrum could easily destroy any other information that might otherwise be present in the spectra. 

Figure 15. Transmission spectrum of water vapour over a 1 m path length at STP (transmission data obtained from HITRAN database).

The photon flux onto the atmosphere can be absorbed at all wavelengths and the absorpdon spectrum of water does just that, absorbing radiadon in the UV, visible,... 

Fig. 7.1 gives a size spectrum of water-borne particles. Particles with diameters less than 10 pm have been called colloids. In soils, the clay-sized and fine silt-sized particles are classified as colloids. Colloids do not dissolve, but instead remain as a solid phase in suspension. Colloids usually remain suspended because their gravitational settling is less than 10 2 cm s 1. Under simplifying conditions (spherical particles, low Reynolds numbers), Stokes law gives for the settling velocity, vs... 

For a fluorescence detector, quinine sulfate is used as the standard compound. The flow cell is filled with a standard solution and the fluorescence intensity is measured. The value is compared with that measured by a fluorescence spectrophotometer. This standard solution is also used for fixing the wavelength and position of the flow cell. The Raman spectrum of water can also be used for this purpose. 

The differences in selection rules between Raman and infrared spectroscopy define the ideal situations for each. Raman spectroscopy performs well on compounds with double or triple bonds, different isomers, sulfur-containing and symmetric species. The Raman spectrum of water is extremely weak so direct measurements of aqueous systems are easy to do. Polar solvents also typically have weak Raman spectra, enabling direct measurement of samples in these solvents. Some rough rules to predict the relative strength of Raman intensity from certain vibrations are [7] ... 

Figure 11.3 Calculated extinction (a) and absorption (b) by a water droplet of radius 1.0 fim. I he absorption spectrum of water is shown in (c). 

In addition, they see much broader peaks with considerable overlap and the absence of expected baseline resolution. Clearly, it would require the power of a computer to deconvolve such seemingly useless wriggles. But today s computers cost less, run faster, have more memory, and readily lend themselves to such calculations as are necessary to glean useful information from NIR spectra. Compare the spectrum of water and of a natural product like soybeans (Figure 5) water, with its two fairly well defined peaks, is one of a few exceptions to the above description of NIR spectra, while the soybean spectrum is quite typical of what one sees in the real world. 

Figure 5.13 The photoelectron spectrum of water vapour ionizations from the 1b, 3a, and 1b2 orbitals are indicated. Ionizations from the more stable 2a, orbital are not produced by the helium radiation used...

The absorption spectrum of water in the vacuum ultraviolet has been studied by Johns (533) and by Bell (92). Sharp rotational structure has been observed only below 1240 A (533). The 1240 A bands have been assigned to the 1 Bx —, 4, transition and is the lirst member of the Rydberg scries. The absorption coefficients of water in the vacuum ultraviolet have been measured by Watanabe ct al. (1016, 1018) and arc shown in Fig. VI I. The absorption coefficients of D2C) have been measured by Laufcr and McNesby in the region 1300 to 1800 A (601). 

A number of hydration of 21 for sucrose, and of 10 for D-glucose, were found213 from the i.r. spectra of these sugars at 25°, compared to the i.r. spectrum of water at higher temperatures. The same method of determination of hydration numbers was applied221 to eight different sugars at 25°. The influence of temperature and concentration on the hydration number... 

Chamberlain and co-workers (17) have noted that no distinct peak occurs in the infrared absorption spectrum of water below 193 cm.-1. The Raman scattering does give rise to a peak near 60 cm."1 while slow neutron scattering give rise to a number of peaks, including a notable one at 56 cm.-1. This discrepancy implies that a significant number of low frequency oscillations may exist in liquid water with little if any infrared activity. 

Fig. 6. Absorption spectrum of water vapor. This figure is taken from ref. (102) with the permission of the Journal of the Optical Society of America.

In the second derivative spectrum of water shown in Figure 5, three absorption bands which are associated with S0, S, and S2 species, respectively were observed [6]. As temperature decreases, absorbance of S0 decreases, while absorbance of S, and S2 increases. 

Fig. 5.42. 600 MHz H NMR spectrum of water solutions of the Thermits Cua domain at pH 8 and 278 K. Signal i is observable at lower pH (adapted from [120]).

A comparison of the water spectrum of water-methanol mixtures with the spectrum of liquid water shows that the angle distribution of H-bonds is sharper at (3 = 0 and j3 = 180°. The cyclic structures of water with medium (3-values of Fig. 5 seem to... 

Figure3.17 INS spectrum ofAu/Ti02 reacted with H2 and 02 at 523 K for 4 h in flowing H2/02/He (1 1 7) (top line). The INS spectrum of water at 523 K adsorbed on Au/Ti02 is shown for comparison (bottom line) [135].

Figure 1.1. Spectrum of electromagnetic radiation A0 - wavelength in free space, W = hu quantum energy, vr - lowest resonance frequency in the rotational spectrum of water, up - plasma frequency of the ionosphere. Reprinted with the permission from [2],...

---