Extinction coefficient spectrum

For most materials the reflected energy is only 5-10%, but in regions of strong absorptions the reflected intensity is greater. The data obtained appear different from normal tra(nsmission spectra, as derivative-iike bands result from the superposition of the normal extinction coefficient spectrum with the refractive index dispersion (based upon the Fresnel relationships from physics). However, the reflectance spectrum can be corrected by using the Kramers-Kronig (K-K) transformation. The corrected spectrum appears similar to the familiar transmission spectrum. 

FIGURE 4.8. Pyrex glass extinction coefficient spectrum. 

Figure 1 shows the extinction coefficient spectrum of developmental photoinitiator CGI-369. Such spectra are equivalent to absorption spectra but are independent of concentration and thickness. 

The ultraviolet absorption spectrum of thiazole was first determined in 1955 in ethanolic solution by Leandri et al. (172), then in 1957 by Sheinker et al. (173), and in 1967 by Coltbourne et al. (174). Albert in 1957 gave the spectrum in aqueous solution at pH 5 and in acidic solution (NHCl) (175). Nonhydroxylic solvents were employed (176, 177), and the vapor-phase spectrum was also determined (123). The results summarized in Table 1-15 are homogeneous except for the first data of Leandri (172). Both bands A and B have a red shift of about 3 nm when thiazole is dissolved in hydrocarbon solvents. This red shift of band A increases when the solvent is hydroxylic and, in the case of water, especially when the solution becomes acidic and the extinction coefficient increases simultaneously. 

The second comment concerns the possibility of avoiding fixed derivatives, using instead the effect of the temperature on the spectrum. Assuming that the extinction coefficients are independent of the temperature, then the changes in the spectrum should correspond to changes in Kt (In Kj- = -4///RT -I- 45/R). Therefore, in principle it is possible to determine the equilibrium enthalpy without the use of model compounds [95ACA(314)225]. 

The reduced symmetry of the chromophore, which still contains 187t-electrons and is therefore an aromatic system, influences the electronic spectrum which shows a bathochromic shift and a higher molar extinction coefficient of the long-wavelength absorption bands compared to the porphyrin, so that the photophysical properties of the chlorins resulting from this structural alteration render them naturally suitable as pigments for photosynthesis and also make them of interest in medical applications, e.g. photodynamic tumor therapy (PDT).2... 

D. gigas AOR was the first Mo-pterin-containing protein whose 3D structure was solved. From D. desulfuricans, a homologous AOR (MOD) was purified, characterized, and crystallized. Both proteins are homodimers with-100 kDa subunits and contain one Mo-pterin site (MCD-cofactor) and two [2Fe-2S] clusters. Flavin moieties are not found. The visible absorption spectrum of the proteins (absorption wavelengths, extinction coefficients, and optical ratios at characteristic wavelengths) are similar to those observed for the deflavo-forms of... 

A useful measure of the strength or intensity of the colour of a dye is given by the molar extinction coefficient (e) at its 2max value. This quantity may be obtained from the UV/visible absorption spectrum of the dye by using the Beer-Lambert law, i.e. 

Compounds containing doubly bonded tin are highly colored due to a strong absorption in the visible spectrum (77-77 transition of the double bond). The extinction coefficients of the distannene [[(Me3Si)2CH]2Sn]2 (entry 3, Table VII) were found to depend on concentration and temperature5 that for the absorption at 332 nm increases with dilution while that for the 495 nm absorption decreases. This suggests that the absorptions arise from two different species, presumably the distannene and the stannylene. By comparison with the other absorption maxima of doubly bonded tin compounds, the absorption at 495 nm is probably that of the distannene. 

Dihydroxy-4 -vinylbenzophenone was converted to a homopolymer of inherent viscosity 0.57 djfc/g by polymerization with AIBN in dimethylformamide. The UV spectrum of the polymer showed the three absorption maxima characteristic of 2,4-dihydroxy b enz ophenones (at 324, 292 and 248 nm), although the extinction coefficient was depressed in comparison with the 4 -ethyl analogue. 

Thus, E is defined as the product of the energy transfer rate constant, ku and the fluorescence lifetime, xDA, of the donor experiencing quenching by the acceptor. The other quantities in Eq. (12.1) are the DA separation, rDA the DA overlap integral, / the refractive index of the transfer medium, n the orientation factor, k2 the normalized (to unit area) donor emission spectrum, (2) the acceptor extinction coefficient, eA(k) and the unperturbed donor quantum yield, QD. 

The intensity of absorption gives the product G , where G is the observed yield and is the molar extinction coefficient. The absolute value of was determined by Fielden and Hart (1967) using an H2-saturated alkaline solution and an alkaline permanganate-formate solution, where all radicals are converted into Mn042. They thus obtained = 1.09 x 104 M- cm1 at 578 nm, which is almost identical with that obtained by Rabani et al. (1965), who converted the hydrated electron into the nitroform anion in a neutral solution of tetrani-tromethane. From the shape of the absorption spectrum and the absolute value of at 578 nm, one can then find the absolute extinction coefficient at all wavelengths. In particular, at the peak of absorption, (720)/ (578) = 1.7 gives at 720 nm as 1.85 X 104 M 1cm 1. 

Farhataziz et al. (1974a, b) studied the effect of pressure on eam and found that as the pressure is increased from 9 bar to 6.7 Kbar at 23° (1) the primary yield of e decreases from 3.2 to 2.0 (2) hv increases from 0.67 to 0.91 eV (3) the half-width of the absorption spectrum on the high-energy side increases by 35% and (4) the extinction coefficient decreases by 19%, which is similar to eh. The pressure effects are consistent with the large volume of ean (98 ml/M), whereas the reduction in the observed primary yield at 0.1 ps is attributable to the reaction eam + NH4+. Some of the properties of eam have been discussed by several authors in Solvated Electron (Hart, 1965). 

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