UV-VIS difference spectra

Fig. 11 (a) Trinuclear rhenium carbonyl complexes 7 and 8 and (b) UV-Vis difference spectra (Aabs = At - At = 0) of compound 7 in CH3CN at 293 K after irradiation at 366 nm for 0, 1,2, 3, 4, 6 h, and inset shows the emission spectral changes before and after photolysis (reproduced with permission from [39])... 

Fig. 15. UV-Vis difference spectra showing the formation of hexasila-Dewar benzene (29) and subsequent photochemistry (2-MeTHF, 100 K).

Fig. 38. UV-VIS difference spectra of carbonaceous deposits after reaction of methanol on HZSM-5 obtained from thermal treatment of the system at the indicated temperatures. Reprinted from [131] with kind permission of Elsevier Science NL, Sara Burgerhartstraat 25, 1055 KV Amsterdam, The Netherlands...

The data depicted in Figure 7.4 are the UV-Vis difference spectra obtained from equihbrated solutions before and after addition of the respective dipeptide. The analytes His-Ala and Ala-His are clearly distinguishable. It is important to note that the UV-Vis spectra differ not only in terms of amplitude at a certain wavelength, but also in terms of the position of inflection points and maxima. 

Figure 25B shows a series of UV/Vis difference spectra (reduced minus oxidized) for 500 pM cytochrome c in 10 mM Tris HCl, pH 7, buffer containing 0.3 M NaCl [124]. The measurements were made in the same thin-layer cell used for the voltammetry in Fig. 25A. The series of spectra were collected by measuring the absorption spectrum for the progressively reduced form of the protein in 50 mV increments from 0.30 to -0.20 V and subtracting the spectrum for the fully oxidized form at 0.40 V. The spectra were obtained after a 1-minute equilibration time at each potential. A series of positive and negative peaks are observed at the different potentials. The arrows depict the positive peaks that correspond to the reduced form of the protein, and the peaks increase in amplitude as the potential is made more negative.

Therefore no trustworthy results for kinetic analysis conld be obtained from the UV-vis absorption spectra due to the formation of bixin isomers and degradation products at different rate constants. " ... 

The maximum absorption wavelengths in different solvents of many carotenoids can be found in the literature, and the % III/II values are also available for some carotenoids. It is common to find variations of 1 to 3 nm in for the same carotenoid in the same solvent cited in different publications. No identification based simply on the matching of recorded UV-Vis spectra with tabulated data can be done without considering the relationships of structures and the factors influencing light absorption. The principal factors that influence carotenoid UV-Vis absorption spectra are discussed below. 

Fig. 3 a UV-Vis DRS spectra of dehydrated TS-1 catalyst reporting the typical 208 nm (48000cm i) LMCT hand, see Fig. 2h also reported are the four excitation laser lines used in this Raman study near-lR (dotted), visible (full), near-UV (dashed) and far-UV (dot-dashed), b Raman spectra of dehydrated TS-1 obtained with four different lasers emitting at 7 = 1064,422,325, and 244 nm (dotted, full, dashed, and dot-dashed lines, respectively). Raman spectra have been vertically shifted for clarity. Although the intensity of each spectrum depends upon different factors, the evolution of the 7(1125)//(960) ratio by changing the laser source is remarkable. The inset reports the Raman spectrum collected with the 244 nm laser in its full scale, in order to appreciate the intensity of the 1125 cm enhanced mode. Adapted from [48] with permission. Copyright (2003) by The Owner Societies 2003... 

The progressive increase in the extent of POM reduction, as evidenced by the ultraviolet visible diffuse reflectance (UV-vis DR) spectra of catalysts downloaded after different reaction times during catalyst equilibration. 

FIGURE 2.21 Spectral profiles recovered by the PARAFAC model at different pH values based on the deconvolution of UV-Vis absorption spectra, featuring the various anthocyanin secondary monomeric forms. (Reprinted from Levi, M.A.B. et al., Talanta, 62, 299, 2004. Copyright 2004 Elsevier Science B.V. With permission.)... 

The samples used were 10"5 M aqueous solutions of 8-hydroxypyrene-I,3,6-trisulfonic acid trisodium salt (HPTS or 3sPyOH) (Sigma-Aldrich) in buffers of pH 6 and pH 10. UV-Vis absorption spectra of the dye solutions at different pH environments were obtained with a Hitachi U-4001 uv-vis spectrophotometer. 

Figure 3. UV-VIS difference reflectance spectra (unirradiated minus irradiated) of untreated chemimechanical pulp (CMP) after irradiation with light at selected wavelengths.

Spectroscopy. UV-VIS reflectance spectra of the pulps were recorded directly after irradiation in the wavelength range 250-750 nm on a Perkin-Elmer Lambda 15 spectrophotometer equipped with an integrating sphere. The reflectance values (RM, strictly speaking the reflectivity of an infinitely thick specimen) at 457 and 557 nm were taken from the reflectance curves. Difference spectra were calculated by subtracting the spectrum of the irradiated pulp from the spectrum of the unirradiated one. 

Figure 5. UV-VIS difference reflectance spectra from photocycling of peroxide-bleached thermomechanical pulp (TMPB) performed using consecutively two different radiation wavelengths, one causing photoyellowing and the other photobleaching (irradiation period 7 h).

UV-vis absorption spectra of Alq(l) and Alq(2) were studied in the solution and in thin films. No difference was observed in the main absorption peaks in solution and thin films. The absorption and PL measured in the solution and in thin films of the complexes are shown in Fig. 4.14. The synthesized complexes showed strong green emission in the range 522-523 nm. The optical band gap of the materials were determined from absorption edge and using the Tauc relation, which relates the absorbance A, with the band gap as... 

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