Water films, spectral absorption

Fig. 10.10 Spectral absorption characteristic of water films with thicknesses 2 and 10 im. Illustration courtesy of Heraeus Noblelight Ltd.

Nafion film coated on an ITO electrode to understand the structural transformations of the dimer in the Nafion coating during the catalytic water oxidation process . The absorption spectral changes observed during the oxidation scan from 0.4 to 1.4 V (s. SCE) (Fig. lOA) showed a decrease in the absorbance at 655 nm with simultaneous increase in the absorbance at around 450 nm with clear isosbestic points at 430 and 545 nm. In the reductive scan from 1.4 to 0.4 V (vs. SCE) (Fig. lOB), the absorbance at 655 nm increased and a simultaneous decrease in the absorbance at 450 nm was observed with an isosbestic point at 555 nm. The absorbance at 655 nm was almost recovered back. Initially the oxidation of the dimer complex H20-Ru" -Ru "-0H2 leads to the formation of H20-Ru "-Ru -0H2 with an absorption maximum at around 450 nm and further oxidation at higher positive potentials must lead to Ru -Ru formation in a successive oxidation process. The Ru -Ru would be rapidly reduced by water molecules to produce H20-Ru -Ru -0H2 at pH 1. The same in situ spectrocyclic voltammetry experiments at pH 9.3 showed an absorption maximum at around 500 nm with the formation of H20-Ru" -Ru -OH in the Nafion film. In relevant to the absorbances at 450... 

The reactions observed for the dimer complex adsorbed in a Nafion film coated on an ITO electrode at different pH by in situ absorption spectral measurements are summarized as shown in Fig. 11. At higher positive potentials and at potentiostatic conditions, a band at around 450 nm was observed indicating the formation of H20-Ru "-Ru -OH2 at acidic conditions and formation of H20-Ru" "-Ru -OH at basic conditions in addition to the absorbance at 655 nm. This shows that during the catalytic water oxidation process, the diaquo dimer complex exists as an intermediate. In a Nafion polymer membrane, the metal complex is isolated and experiences a micro-heterogeneous environment imposed by hydrophobic fluorocarbon moiety and... 

The influence of the counter anion on the excited state relaxation time of cationic polymethine dyes has also been reported . The fluorescence lifetime is dependent on the anion in weakly polar media but independent in polar media. The fluorescence behaviour of highly concentrated rhodamine GG solutions in methanol and water can be separated into monomer and dimer contributions2. Absorption emission and excitation spectral data support the view that the dye rose bengal forms H-type aggregates in water and polar protic solvents 1. The spectroscopic behaviour of rhodamine 6G in polar and nonpolar solvents as well as in thin glass and PMMA films shows dimer formation occurs and their stabilities have been compared under different conditions. The equilibrium between the neutral... 

Unfortunately, water has very strong absorption in this spectral range, exhibiting extremely wide bands. Most proteins require water as a solvent. To do precision IR spectra of proteins, the optical path of the water must be made very small, on the order of 10 fim or so. If the path length is that small, a very high protein concentration is required, on the order of 10 mM typically. There are two ways to achieve spectra at these protein concentrations, either by forming thin films or by using a cell where the IR beam probes via the evanescent wave of total internal reflection. 

The data shown in Table 19 suggest that the observed spectral transitions of cytosine in water can be explained in terms of the scaled transition energies of the hydrated keto-NlH tautomer within the accuracy of about 0.2 eV except the second transition. However, the error becomes smaller if a comparison is made between the computed transitions of the hydrated keto-NlH tautomer and the observed transitions of the cytosine sublimed film. ° Such a difference between the computed and experimental data is not unexpected since the general features of the cytosine spectrum are found to be solvent dependent. It appears that the absorption peak of cytosine in water near 212 nm (5.85 eV) is shifted to 6.07 eV in the sublimed film experiment. The suggested splitting of the 197 nm (6.29 eV) transition in the form of 202 and 189 nm (6.14 and 6.56 eV, respectively) bands found in CD experiments is neither revealed in the CIS calculations nor in the... 

The mercury-xenon source data for water vapor films deposited on a 77 °K substrate (Fig. 5) indicate that the absorptance decreases with increasing film thickness. Although there are no other experimental data with which these data can be compared, the observed results are in agreement with the theoretical model that is proposed. The data indicate that a lower absorptance results when the source is filtered, and Fig. 6 shows that the filtered source gives the better approximation of the spectral distribution of the extra-terrestrial solar source. It should be noted that a deposit of significant thickness is required for a substantial decrease in system absorptance. For water vapor on CAT-A-LAC Black (initial... 

This approach finesses the difficulties associated with strong water absorptions by simply eliminating water from the specimen. Typically 5-50 pL of liquid is spread on a suitable substrate and allowed to dry, and a transmission spectrum is acquired for the resulting film. In addition to eliminating the spectral interference of water. 

The strongest and most complicated distortions in spectra from IRRAS are expected in the region of the phonon absorption of the substrate. As discussed in Section 2.3.2, these distortions are different for each substrate and can be distinguished only using spectral simulations. Here, monolayers on water are considered, which are of interest from many practical and scientific viewpoints [66, 67], The simulated spectra of a 10-nm anisotropic inorganic film (Fig. 3.27) at (pi = 60° [8] will help to interpret the experimental data. It is evident that the... 

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