Band intensity criteria

Empirical correlation of intensities of absorption bands with the structure of complexes in solutions have been made for lanthanide complexes. It has been recognized that forced electric-dipole transitions of low intensities, in some cases lower in intensity than those of magnetic-dipole transitions, may indicate that the ligand field has point group symmetry with a center of inversion. This criterion has been used in the determination of the ligand field by symmetry of Eu3+ aquo ion [202], The absorption band intensity ratios have been used to show the octahedral structure [49] of lanthanide hexahalide complexes, LnXg. ... 

First, the cis-peak assignment for band III is primarily based on the theoretically estimated energy (54), which appears to be very sensitive to the choice of parameters in the calculation (48,93). In fact, recent theoretical considerations (93) show that changes in parametrization markedly affect the energy but not the relative intensity of the cis peak. The intensity criterion, which... 

An attempt has been made to extend the intensity criterion to insoluble materials, using KBr disks. Satisfactory results have been obtained enabling N-bonded complexes to be distinguished from S-bonded [i81). This technique has been further extended by using a suitable internal standard 60) the C—0 stretching band in salicylic acid (1654 cm ) has been used, and the ratio of the intensity of vcn to the intensity of this band has been suggested as a satisfactory criterion to distinguish N- and S-bonded complexes, provided that known complexes are used for calibration. 

The difference in spectral response for s- and p-polarized light has been used very often to discriminate between adsorbate and solution bands. This criterion has been criticized [27] on the basis that the intensity of the electric field vector for s-polarized light may be very low if the solution layer between electrode and IR window is very thin. This causes the spectrum obtained with s-polarized light to have a very low intensity. In this case the absence of bands with s-polarized light does not necessarily imply the absence of absorbing species in solution. 

In a electronic system all transitions are determined by these relations, in a high-spin i system, however, only the quintet-quintet transitions. The latter may be distinguished from the quintet-triplet transitions by their band positions, as in chromium(II) fluorides, or at least by their band intensities, as in manganese(III) fluorides. The intensity criterion must be handled with some care, however, as the maximum extinction coefficients of intercombination bands may well reach the order of magnitude of spin-allowed bands. Thus the absorption maxima at higher energies, which are of interest here, cannot be definitely localized least in MnFs 18) but neither in the other manganese(III) compounds (see Fig. 6). 

Fig. 12b). Since practically the same spectral shape is obtained at Q-band (35 GHz) (Fig. 12c), the commonly used criterion stating that the shape of an interaction spectrum is frequency-dependent fails to apply in this case. Actually, outer lines arising from the exchange interaction are visible on the spectrum calculated at Q-band (Fig. 12c), but these lines would be hardly detectable in an experimental spectrum, because of their weak intensity and to the small signal-to-noise ratio inherent in Q-band experiments. In these circumstances, spectra recorded at higher frequency would be needed to allow detection and study of the spin-spin interactions. 

The obtained results are in agreement with our previous hypothesis [2-4] that absolute intensities and the distribution of relative intensities of IR bands in the spectra of adsorbed species are sensitive to the chemical activation of the corresponding bonds arising from polarization by adsorption sites. Hence, in addition to the low frequency shifts, intensites can be used as a criterion for chemical activation. Indeed, according to the fundamentals of IR spectroscopy, the intensities of IR stretching bands are proportional to the square of the dipole moment changes (dp) created by the stretching vibrations over the normal coordinates q of these vibrations [6] I °c [dp/d q]2. 

Accordingly the ratio vh/ d i criterion for the nature of the vibrations. In the attempted interpretation given in Table 4, the procedure was first to look for the various possible assignments on the basis of the expected spectral regions, and then to select from these those assignments in which the intensity of the bands of benzene and of the d -... 

Alternatively, peaks areas can be defined manually and the entire volume of the peak integrated. This method is more tolerant of imperfect gels. However, because the bands in native gels are often broad, it is critical to set a uniform criterion (such as pixel intensity) for defining peak boundaries and... 

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