Differential spectra

Figure 1. Differential spectra of CO chemisorbed on alumina-supported Rh particles before and after heating to 420 K in hydrogen. One of the three species of chemisorbed CO remains after heating and can be identified by a bending mode at 478 cm 1, a stretching mode at 586 cm 1, and a stretching mode at 1937 cmr1 as a linear CO species. The other CO species react and/or desorb while producing hydrocarbons on the Rh particles. The dominant species formed has been identified...

Figure 2. Differential spectra of CO chemisorbed on alumina-supported Co particles both before and after heating in hydrogen to 415 K. The chemisorbed CO is seen to react and form hydrocarbons in the tunnel junction. This hydrocarbon species is distinct from that formed on Rh as seen by vibrational modes near 1600...

Figure 3. Differential spectra of CO chemisorbed on alumina-supported Fe particles shown before and after two heatings in hydrogen to 420 K. Some CO reacts to form hydrocarbons on the Fe particles. The rising background seen at low frequencies indicates the formation of magnetic particles, either through sintering or the desorption of CO. The formation of OH in the junction upon heating does not correlate with the formation of a C-O bond nor with the formation of the C-H...

Figure 4. Differential spectra of CO chemisorbed on alumina-supported Ni particles both before and after heating to 425 K. Very little surface hydrocarbon is seen to form on the Ni particles. This lack of surface hydrocarbon reflects the selectivity of such catalysts for methanation over Fisher-Tropsch synthesis.

Important information on this problem has been obtained by Grunze 141). It appears that after CO chemisorption on Pd, the d-band photoemission (UV) is attenuated (differential spectra show a negative band) and two new bands appear due to the chemisorbed CO [(5cr + 7t)-band and (4ff)-band]. A decreasing particle size causes an increase in the apparent BE of all three bands—the shift is almost the same for all three bands. This again indicates that the final photoemission effects could be responsible for the shifts observed. 

Differential spectra of diffused reflection around 230-700 nm were measured with a two-beam recording spectrophotometer with corrected zero line it was constructed in our laboratory to measure the spectra of adsorbed species. Spectra were recorded before and after irradiation with a PRK-2 mercury lamp for 15 minutes of the zeolite sample containing adsorbed amine. 

In contradistinction to the spectra obtained in the mica dispersion, Pseudocyanine, when added to the colloidal silver and silver halide systems of Figures IB and 1C, yielded no H-bands but formed well defined J-bands. The latter also exhibited a weak secondary peak located near the absorption maximum of dissolved, unperturbed dye. Although the position and intensity of the J-band varied with the substrate (4, 17, 38, 61), the differential spectra obtained in these silver systems exhibited marked similarities. An increase in the concentration of the substrate produced in both cases a monotonic change in the absorbance of the M-... 

The FT-IR spectra of a 10 mol.dm ferrocyanide solution (at neutral pH) recorded just after irradiation are represented in Fig. 5(a) for different doses Fig. 5(b) highlights the 2090-2140 cm region of those differential spectra. The negative-going band at 2037 cm represents the loss of ferrocyanide. Just after irradiation, Fig. 5(b) shows that two peaks are observed the first one, located at 2115 cm is attributed to Fe(CN)g whereas the second one is located around 2102 cm h This band was attributed to the Fe(CN)5(OH) ion. Let us point out that the wavenumbers of the infrared bands can be relatively easily modeled using nh initio calculations and that these... 

Due to the mostly poorly differentiated spectra putting up a specfinder system did not seem to be promising here. In view of the small number of exemplary spectra, in our experience it is easily possible to get to an assignment by searching the collection. 

Cytochrome concentration AOD between 424 and 409 of the differential spectra red-ox (a) and (b) ordinate scale 100 x AOD. —, NADPH cytochrome c reductase,... 

Figure A3. Fischer s method, (a) Differential spectra O and O (D = ePS - eA) resulting from substraction of the spectrum of the isolable photoisomer A from the spectra of the two photostationaiy states obtained by irradiation at X and X" (254 nm) and (320nm). The superscript and " indicate the different irradiation wavelengths employed. The observation wavelength is the corresponding irradiation wavelengths, (b) Measured spectrum of isolated photoisomer A (dotted line) and calculated spectrum of pure photoisomer B (solid line).

Figure 7.22 AES sensitivity factors normalized to the CuLMM line for lOkeV electron radiation. Sensitivity factors are calculated from the peak-to-peak heights in differential spectra. (Reproduced with permission from D. Briggs and J.T. Grant, Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications and Surface Spectra Ltd, Chichester. 2003 IM Publications.)...

Why are differential spectra preferred in AES analysis Why are direct spectra often used for quantitative analysis ... 

This semi-deterministic approach is interesting because the basis of reference spectra used for the modelling of real spectra is made up of spectra mixtures and specific mineral or organic compounds, the optical properties of which often explain a part of the UV spectra. The reference spectra of mixtures are statistically representative of the different heterogeneous fractions of wastewater, because they are selected from wastewater fractionation. For each wastewater sample, several nitrations are carried out (1 and 0.025 ixm), and the spectra of the filtrate are acquired. The differential spectra are then considered for the basis constitution (Table 2). 

Figure 11. Differential spectra resulting in a wef weather sample fractionation [18],...

Figure 4. Differential spectra of urban wastewater before and after several filtration...

The comparison of differential spectra between the raw and the filtered sample is interesting (Fig. 6). These spectra are related to the characteristics of suspended solids of samples. The TSS concentrations are, respectively, 502 and 669 mg/L, from upstream to the treatment plant, meanwhile the corresponding spectrum seem to be divided twice. The observed increase can be explained, on one hand, by solids input (by incoming water) or formation (related to the biodegradation), and on the other hand, by the aggregation of colloids in suspended solids [6], This is confirmed by the fact that particles of larger size absorb less in the UV region than smaller ones (see Chapter 6). 

Light emission was shown by our experiments to require negligibly small amounts of reduced FMN which we failed to detect with a spectrophotometer. Therefore, to detect the reduction of FMN in the presence of DTT and NADH we have performed spectrophotometric measurements with double the concentrations of FMN and reducing agents. The marked changes observed in FMN differential spectra confirmed the assumption that FMN is directly reduced by these reagents (Fig. 2). 

In conclusion, it may be said that great care must be exercised in the interpretation of the differential spectra of proteins, since the factors contributing to the spectral changes may be many. Further detailed investigations are necessary for understanding the exact relationship between spectral changes and protein structure. 

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