Intensity ratio differences

Intensity ratio differences were also reported by Heyns and Scharmann to exist between the isomeric methyl < - and /3-tri-O-methyl-D-lyxopyranosides (54). 

Solid COj. Table V summarizes the available data for solid CO. The far infrared absorption spectrum in the lattice mode region was reported first by Anderson and Walmsley (1964) at 77 K and later by Ron and Schnepp (1967) at 20°K. Recently, helium temperature measurements were carried out by Kuan (1969) and 35°K measurements by Brown and King (1970). Of these workers, only Kuan prepared the solid sample from the vapor under equilibrium conditions. The results show that the frequencies of the two infrared active modes are not very sensitive to temperature or to sample preparation. On the other hand, the line widths observed by Kuan are about half those reported by Brown and King. Kuan s line widths are given in Table V. Moreover, the measured intensity ratios differ markedly (both values are listed in the table). 

The position of the Si2p spectmm components for the film of 3000 A thick correlates with the position of the Si2p spectmm components for the sample fracture, whereas their intensity ratios differ. This can be attributed to the difference in the stracture of silicon-oxygen anions - the effect of the stractures with smaller Si-O-Si borrd angles in the film increases. 

The amount of the adsorbed inhibitor was characterized by the sum of the P 2p and the P KLL signals, while the Ca/HEDP molar ratio at the sample surface was determined from the calcium/phosphorus intensity ratio. Differences in the respective photoionization cross sections as well as in the spectrometer efficiency for these elements were taken into account by experimentally determining the ratio of the sensitivity factors from a sample of known stoichiometric composition (CaHP04). 

In Raman spectroscopy the intensity of scattered radiation depends not only on the polarizability and concentration of the analyte molecules, but also on the optical properties of the sample and the adjustment of the instrument. Absolute Raman intensities are not, therefore, inherently a very accurate measure of concentration. These intensities are, of course, useful for quantification under well-defined experimental conditions and for well characterized samples otherwise relative intensities should be used instead. Raman bands of the major component, the solvent, or another component of known concentration can be used as internal standards. For isotropic phases, intensity ratios of Raman bands of the analyte and the reference compound depend linearly on the concentration ratio over a wide concentration range and are, therefore, very well-suited for quantification. Changes of temperature and the refractive index of the sample can, however, influence Raman intensities, and the band positions can be shifted by different solvation at higher concentrations or... 

The question arises whether an internal standard can be relied upon to eliminate physical differences among samples, the Class II deviations of Section 7.8. No clear answer is possible. Variations in intensity ratios with particle size and with length of grinding time have been observed, especially in the analysis of minerals, but these effects seem due primarily to a nonuniform distribution of the internal standard, and not to particle size as such. These two possible causes of nonuniformity are difficult to separate. 

To discuss the effectiveness of internal standards, it is helpful to recall the absorption and enhancement effects the standards are intended to compensate. In the present discussion, we shall ignore the incident beam even though this simplification is not always justified. We have indicated above that an internal standard will hot be completely effective if a change in composition influences the intensity ratio (Equation 7-12). Such influences could arise from differences in the extent to which the two analytical lines are absorbed or from differences in the extent to which the two lines are excited. Let us examine the way in... 

Because XPS is a surface sensitive technique, it recognizes how well particles are dispersed over a support. Figure 4.9 schematically shows two catalysts with the same quantity of supported particles but with different dispersions. When the particles are small, almost all atoms are at the surface, and the support is largely covered. In this case, XPS measures a high intensity Ip from the particles, but a relatively low intensity Is for the support. Consequently, the ratio Ip/Is is high. For poorly dispersed particles, Ip/Is is low. Thus, the XPS intensity ratio Ip/Is reflects the dispersion of a catalyst on the support. Several models have been reported that derive particle dispersions from XPS intensity ratios, frequently with success. Hence, XPS offers an alternative determination of dispersion for catalysts that are not accessible to investigation by the usual techniques used for particle size determination, such as electron microscopy and hydrogen chemisorption. 

The adsorbate-covered clusters yield a UPS difference spectrum with two peaks on either side of the metal d-states. The dominant changes in the intensity ratio of these peaks occur up to 50-atom Ag clusters which can be rationalized in terms of the cluster d band width and IP, which both depend on cluster size. 

Great progress has been made, however, in our later study using in situ SXS [Stamenkovic et ak, 2007a], where, by simultaneously fitting the intensity ratio between two different sets of crystal truncation rod (CTR) data that constrain the fit to the full CTR data [Robinson, 1986 Warren, 1990], it was possible to reveal the elemental concentration profile at the surface (Fig. 8.13c). Based on the in situ SXS results depicted in Fig. 8.13a, the topmost surface layer is confirmed to be 100 at%... 

Mbssbauer spectra can yield valuable information about the abundance of different Mbssbauer sites in a sample from the relative intensities of the corresponding subspectra if the/-factors are known. These, however, depend critically on temperature. Differences for the individual sites must be expected at ambient temperatures however, they all vanish at 4.2 K because f T) approaches one for T 0 (see (2.15)). Often measurements at 80 K are sufficient for reliable estimates of the true intensity ratio of Mbssbauer subspectra. 

With h 6) - 1/sin 0)5(0 — Oq), one obtains the same result as given by (4.58), which implies that the anisotropy of the/factor cannot be derived from the intensity ratio of the two hyperfine components in the case of a single crystal. It can, however, be evaluated from the absolute/value of each hyperfine component. However, for a poly-crystalline absorber (0(0) = 1), (4.66) leads to an asymmetry in the quadrupole split Mossbauer spectrum. The ratio of l-Jh, as a function of the difference of the mean square amplitudes of the atomic vibration parallel and perpendicular to the y-ray propagation, is given in Fig. 4.19. 

The indexed relative sensitivity factor approach obviates the necessity of measuring the relative sensitivity factors from all possible matrices, by transferring relative sensitivity factors for elements between different matrices by using the matrix-dependence of characteristic intensity ratios in the spectra. Calibration curves are constructed relating RSFs for an element in a matrix to the matrix ion species ratio (e.g. M2+/M+ for element M) generated from a single standard. 

All of the soluble polymers (1 and 3-6) give high resolution NMR spectra (1H, 13C, and 31P) that are completely consistent with their proposed structures. As observed for other types of poly(phosphazenes), the 31P chemical shifts of these alkyl/aryl substituted polymers are consistently ca. 15-30 ppm upfield from those of the analogous cyclic trimers and tetramers. Some important structural information is provided by 13C NMR spectroscopy, particularly for the phenyl/alkyl derivatives 3 and 4. These polymers are rare examples of phos-phazenes that contain two different substituents at each phosphorus atom in the chain. Thus, they have the possibility of being stereoregular. The fact that the structures are completely atactic, however, is confirmed by the observation of three doublets in the P-Me region of the 13C NMR spectrum (ca. 22 ppm) in a 1 2 1 intensity ratio. 

The increase in intensity ratio indicates the accumulation of oxygen species on the surface of the electrode. After formation of the thick oxide layer the ratio O/Ru becomes constant. The fact that the adsorbed species do form bonds with the Ru of the electrode surface is clearly shown in the respective UPS spectra for different electrode potentials [74]. 

For recording the intensity ratio at two emission wavelengths, it should possess strongly different emission spectrum but a comparable intensity to that of reporter band. 

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