Spectrum illumination time

Fig. 11 Cr(VI) concentrations versus illumination time (Xe light source filtered to simulate solar spectrum). Filled symbols aerated solutions empty symbols N2- purged solutions. The lines are the results from a kinetic model developed to describe the data. The pH values and the initial concentrations in iM for Fe(III) and for oxalate are given (from [74])...

Fig. 13. (A) Development of EPR signals of photoaccumulated A," and Ao" in untreated, spinach digitonin PS-i particles (top) and ether extracted particles (bottom) illumination time and temperature are indicated for each EPR spectrum (B) Profiles (g-values and linewidths) of the fully developed EPR spectra of the untreated and ether-extracted samples (C) plot of the development of EPR signals of [Ar +Ao ], Ao" and Af in untreated (top) and ether-extracted PS-1 particles (bottom) as a function of illumination time (and illumination temperature). Figure source Itoh, Iwaki and Ikegami (1987) Extraction of vitamin K, from photosystem I particles by treatment with diethyl ether and its effect on the A f EPR signal and system I photochemistry. Biochim BiophysActa893 510,511.

The results of a typical experiment are shown in Fig. 4. In this experiment, both the ATP and ADP concentrations prior to illumination were 200 //M, and the Pi concentration was 5 mM. The figure shows the oxyluciferin luminescence spectrum recorded as a function of illumination time. The increase in luminescence with exposure to actinic light is clear evidence of an increase in ATP concentration with illumination. 

The nitrous oxide/acetylene flame is well known for its strong emissions and thus the modified registration scheme was applied to record the spectra. In total, 4 x 50 spectra have been recorded with an individual illumination time of 12 s. For the sample measurements the nitrous oxide / acetylene flame was turned on, while in the case of blank signal registration the flame was turned off. No additional solution was aspirated by the nebulizer to get the pure spectrum of the flame gases. 

The spectrum in Figure 9 is clearly not yet perfect but it is of acceptable quality, particularly if the short illumination time (300 s) and low laser power (70 mW at the sample) are also taken into account. Together with the above-cited ICP and DCPj data it lends strong support to the view that ROA instrumentation has finally progressed to the point where this powerful chiroptical method will become a generally useful analytical tool. 

Objective Evaluation of Color. In recent years a method has been devised and internationally adopted (International Commission on Illumination, I.C.I.) that makes possible objective specification of color in terms of equivalent stimuli. It provides a common language for description of the color of an object illuminated by a standard illuminant and viewed by a standard observer (H). Reflectance spectro-photometric curves, such as those described above, provide the necessary data. The results are expressed in one of two systems the tristimulus system in which the equivalent stimulus is a mixture of three standard primaries, or the heterogeneous-homogeneous system in which the equivalent stimulus is a mixture of light from a standard heterogeneous illuminant and a pure spectrum color (dominant wave-length-purity system). These systems provide a means of expressing the objective time-constant spectrophotometric results in numerical form, more suitable for tabulation and correlation studies. In the application to food work, the necessary experimental data have been obtained with spectrophotometers or certain photoelectric colorimeters. 

Figures 6 and 7 show the absorption spectra of colloidal CdS and ZnS at various times of illumination. The two colloids were prepared by adding an NaSH solution to solutions of Cd(C10j2 or Zn(C104)2, respectively, colloidal silicon dioxide (commercially available from Dupont Ludox HS30) being present at 6 x 10 M as stabilizer in both cases. The absorption starts in both cases close to the wavelengths that correspond to the photon energies (515 nm or 2.4 eV for CdS 340 nm or 3.7 eV for ZnS) at which the absorptions begin in the macrocrystalline materials. It is seen that illumination causes not only a decrease in the intensity of the absorption spectrum but also a change in the shape of the spectrum. The onset of light absorption is shifted towards...

Fig. 6. Absorption spectrum of 2 lO"" M CdS at various times of illumination > 490 nm) in the presence of air >) Stabilizer 6 10" M colloidal SiOj (Ludox HS30). Initial mean diameter of particles 3 nm...

Cosine smearing. Because instrument volume and experiment time must both be minimized for a planetary Mossbauer spectrometer, it is desirable in backscatter geometry to illuminate as much of the sample as possible with source radiation. However, this requirement at some point compromises the quality of the Mossbauer spectrum because of an effect known as cosine smearing [327, 348, 349] (see also Sects. 3.1.8 and 3.3). The effect on the Mossbauer spectrum is to increase the linewidth of Mossbauer peaks (which lowers the resolution) and shift their centers outward (affects the values of Mossbauer parameters). Therefore, the diameter of the source y-ray beam incident on the sample, which is determined by a... 

What does this time dependent friction look like To answer this, we describe the MD calculated results [5c] for (t) for the reactive asymmetric stretch coordinate for the Cl" + CH3C1 SN2 system in H20 solvent, and its associated Fourier spectrum. The latter is particularly illuminating, since it displays peaks clearly identifiable from the spectrum of the same pure H20 liquid. Thus contributions from the H20 bends and... 

Finally, if the solvent reorganization time is of the order of the excited-state lifetime, the first emitted photons will correspond to wavelengths shorter than those emitting at longer times. In this case, the fluorescence spectrum observed under continuous illumination will be shifted but the position of the maximum cannot be directly related to the solvent polarity. 

Figure 7.7 EPR spectra at 9K. of D. vulgaris [Fe] hydrogenase. (A) H2-reduced enzyme subsequently treated with CO (B-E) Spectra recorded after various times of illumination at 9 K. (F) Spectrum recorded after warming up of the sample to I SO K for 10 min. Reprinted with permission from Patil, et al. (1988) and the American Chemical Society. 

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