Ultraviolet-visible absorption characterization

In principle, absorption spectroscopy techniques can be used to characterize radicals. The key issues are the sensitivity of the method, the concentrations of radicals that are produced, and the molar absorptivities of the radicals. High-energy electron beams in pulse radiolysis and ultraviolet-visible (UV-vis) light from lasers can produce relatively high radical concentrations in the 1-10 x 10 M range, and UV-vis spectroscopy is possible with sensitive photomultipliers. A compilation of absorption spectra for radicals contains many examples. Infrared (IR) spectroscopy can be used for select cases, such as carbonyl-containing radicals, but it is less useful than UV-vis spectroscopy. Time-resolved absorption spectroscopy is used for direct kinetic smdies. Dynamic ESR spectroscopy also can be employed for kinetic studies, and this was the most important kinetic method available for reactions... 

Aryl azides may be characterized by the usual methods of chemical analysis. Their ultraviolet and visible absorption properties described earlier, are distinctive. The weak shoulders at 280 to 290 nm are characteristic and are usually visible if they are not obscured by their major absorption band. For example, phenyl azide itself has X,max 250 nm with shoulders at 277 and 286 nm. In the infrared, arylazides absorb strongly with a peak between 2,100 and 2,160 cm-1 which is often split due to Fermi resonance (Av = 50 cm-1). Elemental microanalysis (forC, H, N) gives the expected values for pure aryl azides. Many examples of UV, IR, and NMR spectra of aryl azides are given in the literature cited. 

Since many atmospheric pollutants such as ozone have absorption bands in the ultraviolet, measurements have also been performed in this spectral region. Recently, it was shown that phase locking within the filaments results in enhanced third harmonic generation [46]. Then, the build-up of the ultraviolet supercontinuum was characterized over both the laboratory and the atmospheric scales. The UV-visible part of the continuum measured in the laboratory with a single filament is presented in Fig. 15.7. At the beginning of filamentation, a third harmonic band with 20 nm bandwidth is generated around 270 nm. Two meters further, the intensity of the third harmonic is reduced and a plateau appears in the UV-Visible region be-... 

Volumes 50 and 51 of the Advances, published in 2006 and 2007, respectively, were the first of a set of three focused on the physical characterization of solid catalysts in the functioning state. This volume completes the set. The six chapters presented here are largely focused on the determination of structures and electronic properties of components and surfaces of solid catalysts. The first chapter is devoted to photoluminescense spectroscopy it is followed by chapters on Raman spectroscopy ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy X-ray photoelectron spectroscopy X-ray diffraction and X-ray absorption spectroscopy. 

ID. Optical Methods of Analysis. Optical methods of analysis of reaction systems are very convenient where they can be applied. The optical properties which characterize the system may be the absorption at one or more particular wavelengths (in the ultraviolet, visible infrared, or microwave region), the refractive index of the mixture, the optical rotation of one or more species, the light-scattering properties of large molecules, or the fluorescent emission of one or more of the substances present. 

Free-base corroles as well as their anionic and monoprotonated adducts are generally characterized by several strong ultraviolet (UV)-visible absorption bands. As is true for the porphyrins, the position and intensity of these bands presumably reflects the extended aromatic conjugation present within the molecule. Indeed the spectra of corroles resemble those of the porphyrins in that there is typically a strong Soret-like transition near 400 nm, as well as three weaker, long-wavelength Q-type transitions in the 500-600 nm spectral region. ... 

Bis(4-imino-2-pentanonato)nickel(II) crystallizes from a benzene-petroleum ether mixture as dark red needles or as fine red-orange needles. The two forms have identical melting points. The compound is very soluble in chloroform, but less soluble in benzene, pyridine, and carbon tetrachloride, and very insoluble in water. The compound crystallizes from pyridine without adduct formation. The compound is diamagnetic and apparently has the trans configuration. Partial resolution in optically active fractions has been achieved by means of a chromatographic technique. Molecular weight determinations indicate that the compound is monomeric in chloroform and benzene solution. The visible absorption spectrum of this compound in chloroform is characterized by a band centered at 552 m/i (e = 43). The ultraviolet absorption maxima for solutions in 1 1 benzene-petroleum ether occur at 298, 348, and 364 m x (e = 4150, 4760, and 4460, respectively). ... 

Ultraviolet-Visible Spectroscopy Ultraviolet-visible (UV-VIS) molecular absorption spectrophotometry (often called light absorption spectrophotometry or just UV-visible spectrophotometry) is a technique based on measuring the absorption of near-UV or visible radiation (180-770 nm) by molecules in solution.35,36 Reference standard characterization by UV-VIS spectophotometry includes determining the absorption spectra and the molar extinction coefficient. These two spectral characterizations are used as identifiers of reference standards. 

The optical properties of ceramics are useful in the ultraviolet, visible, and infrared ranges of the electromagnetic spectrum, and one key quantity used to describe the optical property of a material is the refractive index, which is a function of the frequency of the electromagnetic radiation. Other quantities used to characterize optical performance are absorption, transmission, and reflection these three properties sum to unity and are also frequency dependent. The last three properties govern many aspects of how light interacts with materials in windows, lenses, mirrors, and filters. In many consumer, decorative, and ornamental applications, the esthetic qualities of the ceramic, such as color, surface texture, gloss, opacity, and translucency, depend critically on how light interacts with the material. 

Spectrophotometric analyses are the most common method to characterize proteins. TTie use of ultraviolet-visible (UV-VIS) spectroscopy is t rpically used for the determination of protein concentration by using either a dye-binding assay (e.g., the Bradford or Lowry method) or by determining the absorption of a solution of protein at one or more wavelengths in the near UVregion (260-280 nm). Another spectroscopic method used in the early-phase characterization of biopharmaceuticals is CD. 

The ultraviolet-visible spectra of most compounds are of limited value for qualitative analysis and have been largely superseded by the more definitive infrared and mass spectroscopies. Qualitative analytical use of ultraviolet-visible spectra has largely involved describing compounds in terms of the positions and molar absorptivities of their absorption maxima, occasionally including their absorption minima. Indeed, some organic compounds are still characterized in terms of the number of peaks in the UV-visible spectrum and their absorbance ratios. This is usually the case in phytochemistry and photodiode array chromatography and when the analyst has a limited range of compounds to work with whose spectra are known to differ. In the pharmacopeias, however, absorbance ratios have found use in identity tests, and are referred to as Q-values in the U.S. Pharmacopia (USP). 

The product, a-hydroxymuconic semialdehyde, was isolated and characterized from a large scale incubation. Its elemental analysis, infrared, ultraviolet and visible absorption spectra, and its rapid decomposition to pyruvate by extracts of Pseudomonas aeruginosa T1 (JO) are all consistent with this structure. 

By examining the locations, distribution patterns, and intensities of absorption spectra, one can gain information helpful in the identification of compounds. Unfortunately, interpretation of electronic (ultraviolet-visible) spectra is usually less certain than that of vibrational (infrared) spectra because of the broad overlapping bands that characterize electronic absorption. Even so, a great deal of research effort has been expended in hopes that the structural changes of a molecule and the shifts observed in their electronic absorption spectra can be correlated. On the other hand, absorptivities in the infrared are much lower than at shorter wavelengths, rarely exceeding 1000. As a consequence, electronic (ultraviolet-visible) spectrophotometry is sensitive to a much smaller amount of sample and is quite useful for dilute solutions. 

The formation of a clear zone suggested that the PAN solution containing Ag ions was effective in the inhibition of bacterial growth. The Ag/PAN nanocomposite film, characterized by an X-ray diffraction (XRD], transmission electron microscopy (TEM), and ultraviolet-visible [UV-Vis) absorption spectrophotometer, revealed that crystallized cubic Ag particles with diameters of 5.8 nm were dispersed homogeneously in PAN nanofibers. ... 

Products were characterized by Fourier transform infrared spectrophotometry-attenuated total reflectance (FTIR-ATR), ultraviolet visible (UV-Vis) spectrophotometry, scanning electron microscopy (SEM), and broadband dielectric/impedance spectroscopy (BDS). New absorption bands were observed corresponding to the conjugated pol5mieric units by FTIR-ATR and UV-Vis spectrophotometric analysis. The influence of concentration of PEDOT-PSS and PEDOT on the composite electrospun nanofibers was studied by EIS. Morphologies of electrospun nanofibers were also investigated by SEM. 

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