Banding characteristics

Vibrational transitions, usually associated with simultaneous rotational transitions, occur in the i.r. and near i.r., and give rise to bands characteristic of the vibrational and rotational... 

The Raman spectrum of nitric acid shows two weak bands at 1050 and 1400 cm. By comparison with the spectra of isolated nitronium salts ( 2.3.1), these bonds were attributed to the nitrate and nitronium ion respectively. Solutions of dinitrogen pentoxide in nitric acid show these bands , but not those characteristic of the covalent anhydride , indicating that the self-dehydration of nitric acid does not lead to molecular dinitrogen pentoxide. Later work on the Raman spectrum indicates that at —15 °C the concentrations of nitrate and nitronium ion are 0-37 mol 1 and 0 34 mol 1 , respectively. The infra-red spectrum of nitric acid shows absorption bands characteristic of the nitronium ion. The equivalence of the concentrations of nitronium and nitrate ions argues against the importance of the following equilibrium ... 

In this expression, z is the distance from the surface into the sample, a(z) is the absorption coefficient, and S, the depth of penetration, is given by Eq. 2. A depth profile can be obtained for a given functional group by determining a(z), which is the inverse Laplace transform of A(S), for an absorption band characteristic of that functional group. 

The PTFE film turns black and the product exhibits a 2100-2200 cm" band, characteristic of the C=C bond in the i.r. and Raman spectra. It might be worth noting that, in the experience of some, pure condensed molecules of these types are known to explode violently. 

The R band characteristic for aromatic aldehyde groups (aldehyde n TT bands) occurs in the spectrum of A -methylcotarnine (9a) and that of JV-benzoylcotarnine (9c), which are real aldehydes, at 330 m/i in the form of an inflection. Even in alkaline solution the hypothetical amino-aldehyde form of cotarnine can only occur in amounts not detectable by spectroscopic methods. 

The infrared spectra of 2-, 3-, and 4-acetamido- and 2- and 3-benzamido-pyridine 1-oxides show bands characteristic of the 2-, 3-, or 4-substituted pyridine 1-oxide and of the —NHCOCH3... 

In the I.R. spectrum of pAANa, which is shown in Table 5, the absorption bands characteristic of the carboxylate group (- 00"), the covalent sulphate group (—O—SO2—O—), and the hydroxyl group (—OH) are due to the —COONa interaction with copper sulphate according to the following mechanisms ... 

The in-situ infrared study of H3PW12O40, H4SiWi204o and their caesium, potassium and ammonium salts evacuated at various temperatures revealed that these solids were stable up to 673 K since all the bands characteristic of the polyanions were still present at this temperature. Upon heating above 573 K, the terminal W-Ot band was observed to split into two bands at 980 and 962 cm, as already mentionned [16],... 

A series of spectra taken during TPR of a mixture of NO and O2 are presented in Figure 6. Bands are observed for both mon- and dinitrosyls, together with bands characteristic of NO2 and NO3- species. As the temperature rises, the ratio of nitrosyl to NO2/NO3 bands increases, consistent with what is expected on the basis of equilibrium considerations for the reaction NO + 1/2 O2 = NO2 [35]. 

Azo-bridged ferrocene oligomers also show a marked dependence on the redox potentials and IT-band characteristics of the solvent, as is usual for class II mixed valence complexes 21,22). As for the conjugated ferrocene dimers, 2 and 241 the effects of solvents on the electron-exchange rates were analyzed on the basis of the Marcus-Hush theory, in which the t/max of the IT band depends on (l/Dop — 1 /Ds), where Dop and Ds are the solvent s optical and static dielectric constants, respectively (155-157). However, a detailed analysis of the solvent effect on z/max of the IT band of the azo-bridged ferrocene oligomers, 252,64+, and 642+, indicates that the i/max shift is dependent not only on the parameters in the Marcus-Hush theory but also on the nature of the solvent as donor or acceptor (92). 

Figure 10.6. In situ Fourier transform infrared spectra of decane SCR-NO in the presence and absence of hydrogen on Ag/Al203 at 200°C. Evolution of intensities of the bands characteristic for adsorbed species (monodentate nitrates 1245 cm-1, bidentate nitrates 1295 cm-1, —CN 2150 cm-1 and —NCO 2230 cm-1. 1000 ppm NO, 6vol.%02,750 ppm decane, Oor 1000 ppm H2 (reproduced with permission from Ref. [12]).

To determine which mechanism was correct, the photolysis was studied at low temperature.<55) An intermediate with a strong ketene band at 2115 cm-1 was observed. No bands which could be attributed to the spirodienone could be detected. Warming of the matrix to -70°C caused the loss of the ketene absorption and the appearance of new bands characteristic of the ester (ROH = MeOH), indicating the ketene mechanism to be correct ... 

Irradiation of this compound at 77°K produced bands characteristic of benzaldehyde (vc0 = 1699 cm-1) and a new species with v00 = 1803 cm-1. Upon warming the irradiated sample to -40°C, new bands (v = 900 cm-1) appeared, characteristic of the following compound ... 

IR no bands characteristic of functional groups 200 MHz, solvent CDC13 H, l3C and DEPT spectra... 

Additional adsorption studies were also carried out using para- and ortho-chlorobenzaldehydes (Figure 4). The results obtained with p-chlorobenzaldehyde are very similar to the ones obtained with m-clilorobenzaldehyde and were omitted from this paper for brevity. In contrast, substantial differences are observed in the spectra of adsorbed o-chlorobenzaldehyde. In particular, in this case the 1620 cm"1 band characteristic... 

The material balance is consistent with the results obtained by OSA (S2+S4 in g/100 g). For oil A, the coke zone is very narrow and the coke content is very low (Table III). On the contrary, for all the other oils, the coke content reaches higher values such as 4.3 g/ 100 g (oil B), 2.3 g/ioo g (oil C), 2.5 g/ioo g (oil D), 2.4/100 g (oil E). These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands characteristic of C-H bands (3000-2720 cm-1), C=C bands (1820-1500 cm j have been measured. Examples of results are given in Fig. 4 and 5 for oils A and B. An increase of the temperature in the porous medium induces a decrease in the atomic H/C ratio, which is always lower than 1.1, whatever the oil (Table III). Similar values have been obtained in pyrolysis studies (4) Simultaneously to the H/C ratio decrease, the bands characteristics of CH and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C ratio may be comprised between 0.1 and 0.3 ... 

Increasing the initial concentration of zeaxanthin to 10 4 M, Figure 8.6b, produces a different dependence on the ethanol/water ratio. Under these initial conditions, adding water to a final ethanol/water ratio of 3 2 leads to a distinctly different absorption spectrum than that observed at lower initial concentration. The vibrational structure of the S2 state is preserved and a new absorption band characteristic of J-aggregates appears at 530 nm. When the water content was increased... 

Because protein ROA spectra contain bands characteristic of loops and turns in addition to bands characteristic of secondary structure, they should provide information on the overall three-dimensional solution structure. We are developing a pattern recognition program, based on principal component analysis (PCA), to identify protein folds from ROA spectral band patterns (Blanch etal., 2002b). The method is similar to one developed for the determination of the structure of proteins from VCD (Pancoska etal., 1991) and UVCD (Venyaminov and Yang, 1996) spectra, but is expected to provide enhanced discrimination between different structural types since protein ROA spectra contain many more structure-sensitive bands than do either VCD or UVCD. From the ROA spectral data, the PCA program calculates a set of subspectra that serve as basis functions, the algebraic combination of which with appropriate expansion coefficients can be used to reconstruct any member of the... 

Raman spectroscopy allows chemical identification of single phases and in the imaging mode a description of the morphology. Raman bands characteristic of the two main components PA and PTFE are easily distinguishable, as shown in Figure 6, where pure materials have been used from which to record reference spectra. To identify PTFE in the spectra of the bearing the symmetric C-F... 

The FTIR spectrum for the dried paint resin does have a reasonable match score to and feature bands characteristic of an alkyd resin [5]. Due to the presence of fillers though, the spectral analysis did not allow for a high-quality match to be obtained. Removal of the fillers and subsequent FTIR analysis would provide the best spectroscopic result for the identification of the alkyd type and provide a better comparison to such as the reference vinyl toluene-modified alkyd. 

Figure 11(a) shows the spectrum of adsorbed species on an active catalyst in a hydrogen-ethylene stream. This spectrum appears and stabilizes within minutes after hydrogen is blended into the ethylene stream. Three new bands appear in the presence of hydrogen at 2892, 2860, and 2812 cm-1. The appearance and location of these bands were verified by expanded scale spectra. Experiments at lower ethylene pressures reveal that there is an additional band at about 2940 cm-1 partially obscured in Fig. 11 by overlap of the ethylene spectrum. On a poisoned catalyst, which does not show the ZnH and OH bands, only the bands characteristic of chemisorbed ethylene are seen. 

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