Framework bending modes

Last not least, there is a great variety of proprietary lO-design software that has been developed at research facilities and university institutes. E.g., at the TU Delft the S-matrix oriented software Photonic CAD was established several years ago, an innovative 10 design framework based on Hewlett Packard s Microwave Design System. Actual academic work e.g. addresses modes of bent waveguides, BMS-3D" ° is a quite new bend mode solver of the IRE, Prague, or FDTD-schemes with non-uniform grids, a topic of special importance to improve computational efficiency when multi-scale feature sizes are requested, to name a few of recent tasks, only. 

To further characterize the effect of the ammonia hydrothermal treatment, we compared elemental analysis data and 1R spectra before and after ammonia hydrothermal treatment to quantitatively disclose the role of counterion between the silica framework and surfactants. In Table 2, the N/C molar ratio of the mesoporous materials prior to the ammonia hydrothermal treatment is nearly twice of that after the treatment. Moreover, the IR band at 1383 cm 1, which arises from the N03 stretch bending mode, completely disappears after ammonia hydrothermal treatment [20], These results verify that the existence of nitrate counterion (the nitrate/surfactant 1) between surfactant molecules and silica framework in the acid-made mesoporous materials. The bridging counterion N03 was completely removed after ammonia hydrothermal treatment. 

The INS spectra of zeolites have been calculated by force-field methods [106,107]. Note that the hydrogen atoms follow the displacements of the framework atoms due to the lattice modes (480-970 cm ). The lattice modes (Al-0 and Si-O stretching and bending modes) are therefore observed in the INS spectra—another example of hydrogen riding modes. 

The thermal decomposition of ammonium rho-zeolites- has also been followed by inelastic and quasielastic neutron scattering [112]. As the deammoniation temperature was increased, the assigned vibrational features of the bound ammonium ion at 1452 cm (bending modes), 306-363 cm" (ammonium-coupled pore-opening modes of the zeolite framework), and 80-113 cm" (hindered rotational modes) were foimd to diminish with the emergence of scattering features due to H-rho. 

The interaction between the adsorption sites of a zeolite and a probe molecule perturbs the normal vibrations of the molecule and leads to frequency shifts compared to the gas phase which can be interpreted in terms of the strength and nature of the interactions with the adsorption sites of the zeolite. INS is advantageous for observing such interactions for hydrogenous molecules [116,117]. In the infrared spectra the out-of-plane bending modes and the ring vibrations coupled with CH in-plane bending are obscured by the zeolite framework modes below 1300 em . ... 

Figure 2.19 Left part of panel, (a-h) Qualitative representation of the IR spectroscopic features of weak, medium, and strong A-H- -B or A - -H-B H-bonded complexes. The half-width of the bending modes is (somewhat arbitrarily) assumed to slightly increase upon increasing the hydrogen bond strength. The shaded areas correspond to regions obscured by the skeletal modes of the zeolite framework. Right part of panel, (a -h ) Schematic representation of the correlated evolution of the proton potential as function of the A-H distance in A-H- - -B or A - - -H-B The separation barrier in e -f can be very low, and a potential curve characterized by an asymmetric single flat minimum may be used alternatively. Reproduced with permission from Ref. (11). Copyright 1997 American Chemicai Society.

It was proven, by using exchange with deuterium, that bands around 1000 cm characterize the 6(OH) modes of hydrogen-bonded hydroxyls on oxide surfaces (10). The use of a deuterated zeolite sample allowed the detection of the in-plane O—D bending modes around 880 cm (624), whereas the respective O—H modes are generally masked by the zeohte framework vibrations. 

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