Water spectral signatures

Since water in nature is not pure, there are always some suspended particles in the upper layers of a water body. The reflectivity of water increases and it appears brighter the color being shifted slightly towards longer wavelengths. 

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This simple oxidoreduction reaction involves complex OH - water molecules interactions whose the spectral signatures are assigned to Charge-Transfer-To-Solvent states (CTTS states). Indeed, the anionic precursor of the hydrated OH radical represents an interesting system for the direct investigation of elementary redox events in a protic molecular solution. 

Other studies showed that the oligotrophic ocean areas are dominated by phytoplankton organisms of relatively small size, generally less than 5 jLtm. Therefore, the spectral signatures of the oligotrophic small cell size populations should resemble that of the blue water population, and the eutrophic populations typical of coastal and upwelling regions, which gen-... 

Noise analysis has been particularly fruitfiil in characterizing various aspects of hydrodynamics, as noted above for the specific case of corrosion processes. First of all, multiphase flows were investigated, either gas/water [78], solid/liquid [79, 80], oil/water [81] or oil/brine [82]. In these flows, fluctuations are due primarily either to fluctuations in transport rates to an electrode or to fluctuations in electrolyte resistance. If one phase preferentially wets the electrode, then there may be fluctuations due to variation in the effective electrode area. Each of these phenomena has a characteristic spectral signature. Turbulent flows close to a wall have been investigated by means of electrochemical noise by using electrochemical probes of various shapes, by measuring the power spectral density of the limiting diffusion current fluctuations [83-86],... 

In parallel, other lanthanide ions have also been used in these experiments, in particular, the [Lu2(L )3] complexes with Ln = Eu°, Tb , and, to a lesser extent Sm (with overall quantum yields in water at pH 7.4 of 21%, 11%, 0.38%, and lifetimes amounting to 2.43 ms, 0.65 ms, and 30.4 p,s, respectively). It is possible to perform time-resolved microscopy with these different probes. They have specific spectral signatures, and the discrimination can be done as a fimction of the luminescence intensity as well as a fimction of the lifetime decay of the excited states. A proof of concept has been performed with HeLa cells and is presented in Figure 17. The present probes are localized within the same cell compartment. However, once being addressed to different compartments or different targets (such as receptor at the surface of cell membrane) a specific detection can be envisaged. This concept will be illustrated below. 

SFS technique has been explored in the last years, e.g., to classify the composition of mixtures of heterogeneous CDOM present in natural freshwaters and in their different subtractions [27,28,33,34]. Similar attempts to identify certain structural and functional constituents in natural HMs have been carried out also with the aid of total luminescence spectroscopy [35]. At present, utilizations of fluorescence techniques are increasingly related to solve certain environmental questions, e.g., how does CDOM vary spatially between different aquatic environments/seasons, what is the causative factor for the leaching of natural carbons, are there any spectral signatures that could lead to the identification of CDOM sources In connection with the heterogeneity of CDOMs between different water samples there is no single spectral parameter that could explain the variation but chemometric applications are needed for interpretation of multidimensional excitation-emission matrices [33,35-39]. 

Headrick JM, Diken EG, Walters RS, Hammer NI, Christie RA, Cui J, Myshakin EM, Duncan MA, Johnson MA, Jordan KD (2005) Spectral signatures of hydrated proton vibrations in water clusters. Science 308(5729) 1765-1769... 

Mathias G, Marx D (2007) Structures and spectral signatures of protonated water networks in bacteriorhodopsin. Proc Natl Acad Sci USA 104 6980-6985... 

The splitting of spectral features is one of the most direct signatures for PT to occur [6]. However, such data is only available from high-resolution spectroscopy of small molecules in the gas phase [7-10]. Recently, high-resolution vibrational spectra have been recorded for protonated clusters. In 2003, Asmis et al. [3] reported the vibrational spectram of the shared proton in the protonated water dimer. Johnson et al. used vibrational predissociation spectroscopy to characterize the spectral signature of protonated molecular clusters [11,12). And in 2010, Duncan et al. [13] presented photodissociation IR spectra of water clusters (n = 2 — 5)... 

An example of the spectral signatures of water ice clouds is shown in Fig. 6.2.9 (Curran et al., 1973). As confirmed by the cameras of Mariner 9, the field of view of the infrared instrument contained several white clouds at the time the Tharsis Ridge... 

The object 1 Ceres that is now classified as dwarf planet was the first asteroid where spectral signatures of water were found. Near 3.0 microns an absorption feature indicates the presence of water. From that it was estimated that between 10 and 15% water of hydration may be found on Ceres surface (Lebofsky, 1978 [195]). This was the first evidence of water substance on the surface of an object in the main asteroid belt between Mars and Jupiter. Hydration means that a water molecule is added to the crystal structure of a mineral. This creates a new mineral, usually called a hydrate. 

A study of the spectral signature of water described above showed that 66 percent of the C-class asteroids in the sample investigated have hydrated silicate surfaces. Differences in hydration among different types of asteroids may be understood by the fact that the early Sun had a very strong wind which heated the protoasteroids. 

Yang and Jewitt, 2007 [368] searched for spectral signatures of water ice on Trojan asteroids.Trojans (911) Agamemnon, (617) Patroclus, (1143) Odysseus, and (2797) Teucer were observed. These objects have been independently reported to show possible weak absorptions at 1.7 and 2.3 pm, respectively. If real, the latter features may be due to organic materials present on the surfaces. Trojan (4709) En-nomos has a geometric albedo significantly above the mean Trojan albedo, perhaps because a recent impact has coated part of the surface with freshly excavated ice. 

Fig. 7.1 Spectral signatures of water in the Orion nebula, M42. The distance of this famousobject is about 1 500 Ly. The image is a mosaic of more than 40 individual Hubble Space Telescope (HST) images. Credit ESA/NASA...

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