Ultraviolet radiation absorption

M. Vernet, E.A. Brody, O. Holm-Hansen, B.G. Mitchell (1994). The response of Antarctic phytoplankton to ultraviolet radiation absorption, photosynthesis, and taxonomic composition. In C.S. Weiler, P.A. Penhale (Eds). Ultraviolet Radiation in Antarctica Measurements and Biological Effects (pp. 143-158). American Geophysical Union, Washington, D.C. 

Linear polyenes (butadiene, hexatriene, etc.) absorb ultraviolet radiation. They have absorption maxima at the approximate wavelengths given in Table 6-1. 

UV-VIS Simple ethers have their absorption maximum at about 185 nm and are trans parent to ultraviolet radiation above about 220 nm... 

The concept of a chromophore is analogous to that of a group vibration, discussed in Section 6.2.1. Just as the wavenumber of a group vibration is treated as transferable from one molecule to another so is the wavenumber, or wavelength, at which an electronic transition occurs in a particular group. Such a group is called a chromophore since it results in a characteristic colour of the compound due to absorption of visible or, broadening the use of the word colour , ultraviolet radiation. 

Measurements of ozone (O3) concentrations in the atmosphere are of particular importance. Ozone absorbs strongly in the ultraviolet region and it is this absorption which protects us from a dangerously high dose of ultraviolet radiation from the sun. The vitally important ozone layer lies in the stratosphere and is typically about 10 km thick with a maximum concentration about 25 km above the surface of the earth. Extreme depletion of ozone in a localised part of the atmosphere creates what is known as an ozone hole. 

Electron spin resonance (esr) (6,44) has had more limited use in coal studies. A rough estimate of the free-radical concentration or unsatisfied chemical bonds in the coal stmcture has been obtained as a function of coal rank and heat treatment. For example, the concentration increases from 2 X 10 radicals/g at 80 wt % carbon to a sharp peak of about 50 x 10 radicals/g at 95 wt % carbon content and drops almost to zero at 97 wt % carbon. The concentration of these radicals is less than that of the common functional groups such as hydroxyl. However, radical existence seems to be intrinsic to the coal molecule and may affect the reactivity of the coal as well as its absorption of ultraviolet radiation. Measurements from room... 

A particularly important property of ozone is its strong absorption in the ultraviolet region of the spectrum between 220-290 nm ( max255.3nm) this protects the surface of the earth and its inhabitants from the intense ultraviolet radiation of the sun. Indeed, it is this absorption of energy, and the consequent rise in temperature, which is the main cause for the existence of the stratosphere in the first place. 

Another, more subtle, exception arises when normal molecules absorb ultraviolet radiation. Light absorption causes one electron to jump to a formerly unoccupied orbital and produces a molecule in an excited state . While the molecule is in this excited state, the spin up and spin down electron clouds are not identical. 

For detailed consideration of the relationships between chemical constitution and the absorption of visible/ultraviolet radiation, textbooks of physical chemistry or of spectroscopy should be consulted.12-17 A table of Amax and max values is given in Appendix 10. 

In Section 17.13 reference has been made to the influence of various substituents in the benzene ring on the absorption of ultraviolet radiation, and the purpose of this exercise is to examine the effect in the case of benzoic acid by comparing the absorption spectrum of benzoic acid with those given by 4-hydroxybenzoic acid and 4-aminobenzoic acid. 

Visible and ultraviolet absorption spectra are measured in an absorption spectrometer. The source gives out intense visible light or ultraviolet radiation. The wavelengths can be selected with a glass prism for visible light and with a quartz prism or a diffraction grating for ultraviolet radiation (which is absorbed by glass). A typical absorption spectrum, that of... 

Once the FBA has been identified, ultraviolet absorption spectroscopy affords a rapid and accurate method of quantitative analysis. Care must be taken when interpreting the spectra of stilbene-type compounds, since turns to cis isomerisation is promoted by ultraviolet radiation. Usually, however, a control spectrum of the turns isomer can be obtained before the compound undergoes any analytically significant isomerisation. FBAs are often marketed on the basis of strength comparisons determined by ultraviolet spectroscopy. 

Figure 11.4 Analysis of in vitro synthesized RNAs. 32P-Radiolabeled RNAs (48 nucleotides) capped with m7Gp3G (A and C) or m27,3 °Gp3G (B and D) were digested with either RNase T2 (A and C) or RNase T2 plus tobacco acid pyrophosphatase (TAP) (B and D) followed by anion-exchange HPLC on a Partisil 10SAX/25 column as described in the text. Fractions of 1 ml were collected, and the Cerenkov radiation was determined. The elution times of the following standard compounds, detected by ultraviolet (UV) absorption, are indicated with arrows 3,-CMP (Cp), S UMP (Up), 37-AMP (Ap), 3 -GMP (Gp), 3, 5 -m7GDP (pm7Gp), 3, 5 -GDP (pGp), 5 -GDP (p2G), 5 -GTP (p3G), and guanosine-SCtetraphosphate (P4G).

Millward and Bihan [59] studied the effect of humic material on the determination of mercury by flameless atomic absorption spectrometry. In both fresh and seawater, association between inorganic and organic entities takes place within 90 min at pH values of 7 or above, and the organically bound mercury was not detected by an analytical method designed for inorganic mercury. The amount of detectable mercury was related to the amount of humic material added to the solutions. However, total mercury could be measured after exposure to ultraviolet radiation under strongly acid conditions. 

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