Water optical absorption

A key issue is the improvement of solar light harvesting. New active materials with high optical absorption in the visible and good photostability are needed. Implementation of carrier multiplication through impact ionization in quantum dots arrays could mitigate the losses related to carrier thermalization. The alternative approach is the development of vertically stacked tandem systems of increasing band gap active materials, which effect H+ reduction and water oxidation on opposite sides. 

Table 1 Formation Rate Constants (mol 1 sec and Optical Absorption Maxima of Metal Atoms, Hydrated or Complexed, and of the Corresponding Charged Dimers in Water [19]...

The optical absorption spectra depend on the solvent. They are red-shifted with the decreasing polarity of the solvents as in EDA, liquid NH3, where they appear at a longer wavelength than in water [49], and blue-shifted in methanol [38]. Moreover, the maximum in NH3 is red-shifted with the increase of temperature. In water, the Ag band is almost unchanged in the range 20-200 °C, while that of Ag2 is markedly shifted to the red [50]. Electron spin echo modulation analysis of Ag in ice or methanol glasses has concluded to a charge transfer character to solvent (CTTS) of the absorption band [51]. 

Pitts et al. (1985) first used differential optical absorption spectrometry (DOAS) to establish unequivocally that N02 injected into a mobile home forms HONO. Interestingly, the dependence of the rate of HONO generation on the N02 concentration was similar to that measured in laboratory systems, consistent with production in, or on, a thin film of water adsorbed on surfaces. A number of studies have confirmed that the behavior is similar to that in laboratory systems i.e., the rate of production of HONO increases with N02 and with relative humidity. Indoor levels of HONO as high as 8 ppb as a 24-h average and 40 ppb as a 6-h... 

However, the cell in Fig. 9.2(b) has a disadvantage in that the concentration of the electrogenerated substance decreases with increasing distance from the OTE surface. Because of this, simulation of the reaction is very difficult, except for the first order (or pseudo-first-order) reactions. For more complicated reactions, it is desirable that the concentration of the electrogenerated species is kept uniform in the solution. With a thin-layer cell, a solution of uniform concentration can be obtained by complete electrolysis, but it takes 30 s. Thus, the thin-layer cell is applicable only for slow reactions. For faster reactions, a column-type cell for rapid electrolysis is convenient. Okazaki et al. [7] constructed a stopped-flow optical absorption cell using one or two column-type cells (Fig. 9.4) and used it to study the dimerization of the radical cations (TPA +) of triphenylamine and the reactions of the radical cation (DPA +) of 9,10-diphenylanthracene with water and alcohols. Using the stopped-flow cell, reactions of substances with a half-life of 1 s can be studied in solutions of uniform concentrations. 

The 77-SCF MO Cl method has also been used446 to interpret spectral transitions of a series of possible intermediates in the reaction of uracil and cytosine with the solvated electrons eaq, produced by radiolysis of water. Experimentally this reaction has been investigated by Hayon,447 who used the technique of flash radiolysis. Hayon measured the optical-absorption spectra of the transient species in the UV range to obtain information on the site of attack of eaq on the pyrimidine base. At pH 5.0 the solvated electrons react with the pyrimidine molecules mainly at the C-2 and C-4 carbonyls, and the intermediates are rapidly protonatcd to give the corresponding ketyl radicals. For uracil Hayon found two absorption maxima (at 305 and < 280 nm) at pH 5.1 and one peak at 310 nm at pH 11.7. In this last case, on ionization of one of the chromophores the ketyl radical anion of the other nondissociated carbonyl is formed. Several species, 44, 45, 46, have been suggested by... 

The optical absorption spectra of et consist of one broad structureless band whose position and width also depend on the nature of the solvent. As an example, Fig. 5 presents an optical spectrum of et in a 10 M NaOH + -H20 matrix recorded at 77 K. The nature of the transition responsible for this band can be different in different media. For example, in water-alkaline matrices this band seems to correspond to the transition of an electron to a... 

Vapour pressures for a number of atmospherically relevant condensed systems have been measured with mass spectrometry. These systems include hydrates of HC1, HjS04 and HNO, supercooled liquids and pure water-ice, as well as the interactions of HC1 vapour with die solids, ice and NAT [23,47,50-55]. Vapour pressure measurements over HNOj/HjO hydrates have also been made using infrared optical absorption with light originating from a tunable diode laser [29]. This technique allowed the identification of the metastable NAD in presence of the more stable NAT under temperature and vapour pressure conditions near to those found in the polar stratosphere. Vapour pressures of Up, HN03, HC1, HBr over supercooled aqueous mixtures with sulfuric acid have been calculated using an activity model [56]. It provides a parameterized model for vapour pressures over the stratospheric relevant temperatures (185-235 K). 

Rate studies of the reaction between cesium and water in ethylenediamine, using the stopped-flow technique, have been extended to all alkali metals. The earlier rate constant (k — 20 NT1 sec.-1) and, in some cases, a slower second-order process (k — 7 Af"1 sec.-1) have been observed. This is consistent with optical absorption data and agrees with recent results obtained in aqueous pulsed-radiolysis systems. Preliminary studies of the reaction rate of the solvated electron in ethylenediamine with other electron acceptors have been made. The rate constant for the reaction with ethylene-diammonium ions is about 105 NCl sec.-1 Reactions with methanol and with ethanol show rates similar to those with water. In addition, however, the presence of a strongly absorbing intermediate is indicated, which warrants more detailed examination. 

Earlier work (6) using this method yielded a second-order rate constant of 24.7 1.5 M""1 sec."1 for the reaction of dilute solutions of cesium with water in ethylenediamine. On the basis of optical absorption spectra (7) and other evidence (8, II), it was assumed that this reaction was that of the solvated electron as well as loosely bound electrostatic aggregates of electrons and cations with water. This permitted correlation with the results of aqueous radiation chemistry. 

Hart and Boag s discovery (13) of the broad optical absorption band of the e aq in irradiated water confirmed the conclusion (7, 8) that the eaqy instead of the H atom, is the principal reducing intermediate in the bulk of the solution. Understandably, the Lea-Platzman (31) viewpoint of the primary physical processes of energy absorption gained currency over the Samuel-Magee (34) viewpoint. Their disagreement concerned the fate of the electron from primary ionization of water Platzman (31)... 

Jortner J, Rabani J (1962) The decomposition of chloroacetic acid in aqueous solutions by atomic hydrogen. I. Comparison with radiation chemical data. J Phys Chem 66 2078-2081 Keene JP (1963) Optical absorptions in irradiated water. Nature 197 47-48... 

Green, S. A., and N. V. Blough. 1994. Optical absorption and fluorescence properties of chromophoric dissolved organic matter in natural waters. Limnology and Oceanography 39 1903-1916. 

The fullerenecontaining polymers of acrylamide (FPAA) or acrylic acid (FPAAcid) turned out to be soluble in water and in their optical absorption spectra demonstrate an absorption in region from 240 nm up to 700 nm whereas in... 

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