Ultraviolet -visible absorption data

Table 2. Ultraviolet-visible Absorption Data for Typical Polysilanes ...

Low-temperature, photoaggregation techniques employing ultraviolet-visible absorption spectroscopy have also been used to evaluate extinction coefficients relative to silver atoms for diatomic and triatomic silver in Ar and Kr matrices at 10-12 K 149). Such data are of fundamental importance in quantitative studies of the chemistry and photochemistry of metal-atom clusters and in the analysis of metal-atom recombination-kinetics. In essence, simple, mass-balance considerations in a photoaggregation experiment lead to the following expression, which relates the decrease in an atomic absorption to increases in diatomic and triatomic absorptions in terms of the appropriate extinction coefficients. 

Tab. 7.5 Ultraviolet-visible absorption bands and electron transitions for the iron oxides (data for magnetite, A/ustite and akaganeite from Strens Wood, 1979 A/ith permission bernalite from McCammon et al.,1995 remainder from Sherman Waite, 1985 A/ith permission)...

Ultraviolet-visible absorption bands (in deionized water) appear at 440 (w), 322 (s), and 234 (s) nm, in close agreement with published data for the chloride. ... 

We have compared the ultraviolet-visible absorption and emission characteristics of the model compounds (4, 5, 6) with those of the copolymers (1, 2, 3). The comparisons were conducted in methanol solution and in coating of the polymers upon quartz. In order to compare the model compounds (4, 5, 6) with the polymers, as coatings, mixtures of the model compounds (4, 5, 6) in the parent polymer, poly-(5-vinyl-2-methylpyridinium methosulfate), were coated upon quartz plates. The comparative data of the absorption and emission characteristics of the various experimental combinations are summarized in Table I. 

We have found a direct calorimetric determination of both K and AH° to be capable of producing much more reliable thermodynamic data than infrared or ultraviolet-visible spectroscopy. Furthermore, things that react extensively have enthalpies but may not have convenient changes in absorption bands. The procedure for the simultaneous determination of K and AH° from calorimetric measurements has been described (20—22). 

Table 4.15. Ultraviolet and Visible Absorption Spectra Data of Fulgide 60 (E) and its...

Ultraviolet-visible (UV-Vis) spectroscopy was used to monitor synthesis and decomposition of dithiiranes 25a with an absorption maximum at 442 nm, and 25b with an absorption maximum at 438 nm <1995TL1867>. The UV-Vis spectra of dithiiranes 21, 8, 23a, and 22 reveal the absorption maximum in a range of450-455 nm due to the S-S bond <2003JOC1555>. UV-Vis spectroscopic data for dithiiranes are collected in Table 1. 

While all types of spectral data can be compiled, the data of most interest to the analytical chemist are those which lend themselves to a quantitative assay. Infrared, ultraviolet, and visible absorption spectroscopy plus... 

The techniques of infrared emission, ultraviolet and visible absorption and emission, and time-of-flight mass spectrometry have also been utilized and will be discussed along with a general description of the shock tube method and various methods of data reduction and refinement. 

Ouantitative IR absorption methods differ somewhat from ultraviolet-visible molecular spectroscopic methods because of the greater complexity of the spectra, the narrowness of the absorption bands, and ilie instrumental limitations of IR instruments. (Quantitative data obtained with older dispersive IR instruments were generally signilicantly inferior in quality to data obtained with UV visible speclrophotomelers. 1 he precision and acciir icyof measurements with modern F TIR iustrumenis, however, is distinctiv betler than those... 

The ultraviolet-visible spectrum is generally recorded as a plot of absorbance versus wavelength. It is customary to then replot the data with either e or log e plotted on the ordinate and wavelength plotted on the abscissa. Figure 7.4, the spectrum of benzoic acid, is typical of the manner in which spectra are displayed. However, very few electronic spectra are reproduced in the scientific literature most are described by indications of the wavelength maxima and absorptivities of the principal absorption peaks. For benzoic acid, a typical description might be... 

In a large portion of routine and discovery-oriented analyses, mass spectrometry (MS) is used as a qualitative technique. The obtained qualitative data enable detection and structural elucidation of molecules present in the analyzed samples. However, modern chemistry and biochemistry heavily rely on quantitative information. In biochemistry it is often sufficient to conduct quantification of analytes in biofluids every few hours, days, or even weeks. In the real-time monitoring of highly dynamic samples, it is necessary to collect data points at higher frequencies. When it comes to selection of techniques for quantitative analyses, especially in the monitoring of dynamic samples, MS has not generally been favored. In fact, the performance of MS in quantitative analysis is worse than that of optical spectroscopies - especially, ultraviolet-visible (UV-Vis) absorption and fluorescence spectroscopy. 

Studies of ultraviolet and visible absorption spectra started long before the study of infrared absorption spectra, and a far larger number of spectral measurements is available. Still, they have not been fully utilized for the identification of organic compounds and the most important reason for this state of affairs is that these data have not been organized from the point of view of the absorbing system, as outlined above. 

In that publication, rules were proposed for notation and for the order of the absorbing systems. The collection of data was certainly useful in utilizing ultraviolet and visible absorption spectra, but it included only a table for identifying absorption maxima from absorbing systems and no table in which the absorbing systems could be found from the absorption maxima, which would be the most convenient method for structural identification. 

Many metal complexes and clusters are colored and have distinctive ultraviolet-visible spectra. [80] The method offers the advantage of ease of application, but it has been used only seldom in the characterization of zeolite entrapped oigano-metallics. The spectra may provide evidence of metal-metal bonds, as has been shown for carbonyl clusters of Fe, Ru, and Os, [81, 82] but there are hardly any data for zeolite entrapped clusters. The absorption bands of dusters are shifted to lower energy as the cluster nudearity increases. [83] Ultraviolet-visible spectroscopy has been used to detect the formation of [HFe3(CO)n] in NaY zeolite [50] and of clusters suggested to be [Pt,(CO),g] in NaY zeolite. [40-42] Since the spectra do not provide highly spedfic structural information, the method is of secondary importance. 

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