Intra structure-insensitivity

The observed bands were classified by Flanigen et al. [112] into two types, namely internal modes of the TO4 tetrahedra ( intra-tetrahedral modes, cf. Sect 5.2) and external modes ( inter-tetrahedral modes) of the zeolite fi-amework. Table 1 summarizes the zeolite infrared assignment according to the FKS correlation. The internal vibrations represent structure-insensitive modes, and no distinction has been made between the modes of Si04 and AIO4 tetrahedra. The bands of external modes were observed to be sensitive to the structure, and their positions in the spectra are shifted in dependence on the framework topology and on the nsi/n i ratio. Even though this classification proved to be very successful in many applications, from a theoretical point of view such a division into... 

In a similar way, bands between 650 and 500 cm were attributed to inter-tetrahedral vibrations of double four-membered rings (D4R, as, e.g., in A-type zeolites) or double six-membered rings (D6R as, e.g., in X- and Y-type faujasite). Again, it must be stressed that the assigmnent of inter-tetrahedral modes to ring vibrations (ej, 02 see Table 1) soon became a matter of debate and deviating interpretations were advanced (cf. Sect 2.5 and Refe. [113,240]). The intra-tetrahedral vibrations were shown to be essentially structure-insensitive. This became evi-... 

H-N.m.r. spectroscopy has contributed significantly to extensions of our knowledge on the structure and conformation of biomolecules as well as on intra- and inter-molecular, interaction processes. N.m.r. spectroscopy is, however, an inherently insensitive technique, and the richness of information contained in an n.m.r. spectrum often limits the size and complexity of the molecules that can usefully be studied. 

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