By Karge H.G., Weitkamp J. (eds.)
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Additional info for Molecular Sieves, Science and Technology vol.4 Characterization I
7). It is worthy to note that IR spectroscopy was also relatively early employed to identify and investigate framework vibrations (vide supra, cf. [112, 114] and Sect. 2). In these experiments, usually the so-called KBr-technique was used (cf. Sects. 2). , the nSi/nAl ratio of the zeolite framework were disclosed and discussed. Furthermore, with the advent of improved instrumentation and experimental techniques interesting in-situ investigations became possible which were related, for instance, to the synthesis of and heterogeneous catalysis on zeolites, catalyst deactivation, diffusion or solid-state ion exchange as well as other postsynthesis modifications.
The spectrum of the strayed light contains, besides the signal of the exciting light at n˜0, weaker so-called Raman lines appearing at wavenumbers n˜Ra = n˜0 – n˜s (Stokes lines, red-shifted) and (with even lower intensities) n˜Ra = n˜0 + n˜s (antiStokes lines, blue-shifted). They result from vibrations and rotations of the scattering species. Stokes lines in the Raman spectrum are due to those species which, after excitation, do not return into the ground state but into a vibration state of higher energy level.
G. Karge · E. Geidel cases below 1300 cm–1), where the transmittance of the zeolite materials is already rather low. The results presented in Refs. [112, 114] were frequently used in the practice of zeolite characterization, especially the reported correlations between band positions and nSi/nAl ratios of the zeolite samples. Therefore, this study by Flanigen et al.  on framework vibrations will be briefly reviewed here. From a theoretical point of view, the authors’ interpretation of their findings is, however, questionable, as discussed in Sect.