IR edge

For ZBLAN, the IR edge is in the 5-8 m range with a 50% transmission located at 7.1 /on (1400 cm-1) for a 2 mm-thick sample. This is to be compared with silica glass whose transparency starts decreasing at 3 pm. The IR edge is due to multiphonon absorption processes related to the fundamental vibration frequencies... 

IR edge is shifted towards longer wavelengths, as compared to ZBLAN. 

Figure 16.13 Infrared absorption edges of select ceramic crystals. Note the correlation between the IR edge and the melting points of the solids.

With regard to IR sources, in addition to the development of IR edge radiation in the recent years, interest is steadily increasing in the science of... 

In 1960, Harrick demonstrated that, for transparent substrates, absorption spectra of adsorbed layers could be obtained using internal reflection [42]. By cutting the sample in a specific trapezoidal shape, the IR beam can be made to enter tlirough one end, bounce internally a number of times from the flat parallel edges, and exit the other end without any losses, leading to high adsorption coeflScients for the species adsorbed on the external surfaces of the plate (Irigher than in the case of external reflection) [24]. This is the basis for the ATR teclmique. 

Fig. 2.4. The asymptotic behaviour of the IR spectrum beyond the edge of the absorption branch for CO2 dissolved in different gases (o) xenon (O) argon ( ) nitrogen ( ) neon (V) helium. The points are experimental data, the curves were calculated in [105] according to the quantum J-diffusion model and two vertical broken lines determine the region in which Eq. (2.58) is valid.

If a vacant site is occupied by another Nb atom, such that it is a dimer, new catalysts may be designed. The Nb dimer catalyst(2) was prepared by reaction of [Nb(ri -C5H5)H-p-(T, Ti -CsH4)]2 with a Si02 at 313 K, followed by treatment with 02 at 773 K. A proposed structure(2) was characterized by EXAFS, x-ray absorption near-edge structure(XANES), FT-IR, UV-vis, and XPS, which shows Nb-Nb (coordination number 0.9) and Nb-Si(2.3)... 

The IR spectra in Fig.7 indicate the preferential adsorption of NO on the Co sites. It may be conjectured that the Mo sulfide species are physically covered by the Co sulfide species or that Co-Mo mixed sulfide species are formed and the chemical natures of the Co and Mo sulfides are mutually modified. The Mo K-edge EXAFS spectra were measured to examine the formation of mixed sulfide species between Co and Mo sulfides. The Fourier transforms are presented in Fig.8 for MoSx/NaY and CoSx-MoSx/NaY. The structural parameters derived from EXAFS analysis are summarized in Table 1. The structure and dispersion of the Mo sulfides in MoSx/NaY are discussed above. With the Co-Mo binary sulfide catalyst, the Mo-Co bondings are clearly observed at 0.283 nm in addition to the Mo-S and Mo-Mo bondings. The Mo-Co distance is close to that reported by Bouwens et al. [7] for a CoMoS phase supported on activated carbon. Detailed analysis of the EXAFS results for CoSx-MoSx/NaY will be presented elsewhere. It is concluded that the Co-Mo mixed sulfides possessing Co-S-Mo chemical bondings are formed in CoSx-MoSx/NaY. 

Figure 9.19 The Pt and Ir L3 edge in situ XANES spectra for Pto.8lro.2/Pd/C (20 nmol Pd) in 1 M HCIO4 at 0.47 V. The Pd loading in these nanoparticles has been doubled to enhance the Ir signal in the specific experiment. (Reproduced with permission from Vukmirovic et al. [2007].)...

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