Diffuse band assignments

The skeleton vibrations. C3NSX, CjNSXj. C NSXY, or C NSXj (where X or Y is the monoatomic substituent or the atom of the substituent which is bonded to the ring for polyatomic substituents), have been classified into suites, numbered I to X. A suite is a set of absorption bands or diffusion lines assigned, to a first approximation, to a same mode of vibration for the different molecules. Suites I to VIII concern bands assigned to A symmetry vibrations, while suites IX and X describe bands assigned to A" symmetry vibrations. For each of these suites, the analysis of the various published works gives the limits of the observed frequencies (Table 1-29). 

Diffuse reflectance infrared spectra were acquired for the sorbitol samples. As shown in Figure 7, identical IR spectra were observed for all materials. The IR spectral band assignments are presented in Table 9, and the measured absorbance bands are consistent with the structure of sorbitol. 

FTIR spectra in the near-IR region consist entirely of overtones and combinations of primary bands within the mid-IR region. For macromolecules or complex mixtures, the excessive overlapping of bands produces a diffuse absorption continuum with few characteristic features, making unequivocal band assignment practically imposssible. Thus, this spectral range has a limited use in qualitative analysis. Even so, a major asset of near-IR analysis is the ease with which reproducible spectra can be obtained by reflectance and transreflectance (a combination of transmission and reflectance) techniques in every state of aggregation without complicated sample preparation. 

Fig. 3-1. Band assignment for the diffuse reflectance spectrum of a goethite. Note that one band eould not be assigned. EPT electron pair transition OMCT oxygen-metal charge transfer. From Seheinost et al., 1999 with permission.

Kutner et al. [05Kut] report on the detection of a narrow diffuse band, in absorption and emission near 212.5 nm, which they assign as originating from the Og (5 So) - lu (6 Si) electronic transition of Cd2. 

Another tissue type—nails— was studied by Sowa et al., both in vivo and ex vivo [122]. Mid-IR (MIR) and NIR spectra were collected for viable and clipped human nails. Depfh profiling by MIR was performed non-intrusively by phofoacousfic specfroscopy (PAS). Near-infrared ATR, NIR diffuse reflecfance, and PAS were compared. Band assignments were made, such as the N-H stretch-amide II bend combination centered at 4868 cm in this basic study. They concluded that the lower-energy NIR-ATR, for purposes of fheir sfudy, gave the best results. 

Vinyl acetate/vinylchloride copolymers were analyzed with diffuse reflectance and photoacoustic technique. The 2150-nm band, assigned as an ester carbonyl, was used [61]. Ethylene/vinyl acetate copolymer was quantified using an InfraAlyzer 500 and a rotating cup drawer. Vinyl acetate was... 

The CHjO absorption in the 175 nm region is dominated by a strong band which was assigned by Allison and Walsh to the Rydberg transition derived from n - 3s excitation. In addition to the normal vibrational fine structure at -1-1577 and -f-2660 cm , which was assigned to the 2 and 1 vibrational quanta, diffuse bands appeared at -f-346 and 4-822 cm . These intervals are too small to be accounted for by harmonic vibrations. It has been suggested that the upper electronic state is... 

The out-of-plane vibrations of thiazole correspond to C-type vibration-rotation bands and the in-plane vibrations to A, B, or (A + B) hybrid-type bands (Fig, 1-9). The Raman diffusion lines of weak intensity were assigned to A"-type oscillations and the more intense and polarized lines to A vibration modes (Fig. I-IO and Table 1-23). 

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