Absorption bands number

Figure 4.17 Infrared spectra showing degree of cure of DGEBA epoxy resin by changes in the 912 cm absorption band. ° (Number indicates the cute time in hours.)...

In current practice, rationalized units are not used in IR the absorption bands have long been identified in terms of wavelengths, i. e., in micrometers. The general trend now is to express energy by a scale proportional to the frequency the wave number designated by v is defined as (... 

The intensity of a spectral absorption band at a given wave length is expressed in terms of absorption or extinction coefficients, dehned on the basis of the Beer-Lambert law. The latter states that the fraction of incident light absorbed is proportional to the number of molecules in the light path, i.e., to the concentration (c) and the path length (1). The law may be expressed mathematically as ... 

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). 

It is equivalent, when an ftk spectrometer is used, to re-apodization of the data. Curve fitting is a method of modeling a real absorption band on the assumption that it consists of a series of overlapped peaks having a specific lineshape. Typically the user specifies the number of peaks to attempt to resolve and the type of lineshape. The program then varies the positions, sizes, and widths of the peaks to minimize the difference between the model and the spectmm. The largest difficulty is in knowing the correct number of peaks to resolve. Derivative spectra are often useful in determining the correct number (18,53,54). 

The farther into the uv and the narrower the distribution of the resonant electron frequencies, the smaller the effect of dispersion in the visible region. The Pb(II) ion exhibits absorption in the near-uv, and addition of Pb(II) to a glass increases both n and dispersion. However, the use of Ba(II) and La(III) increases n without increasing dispersion. Fluorophosphates, having absorption bands located well into the uv, are examples of glasses with high AbbH numbers and low refractive indexes. 

A number of analytical methods have been developed for the determination of chlorotoluene mixtures by gas chromatography. These are used for determinations in environments such as air near industry (62) and soil (63). Liquid crystal stationary columns are more effective in separating m- and chlorotoluene than conventional columns (64). Prepacked columns are commercially available. ZeoHtes have been examined extensively as a means to separate chlorotoluene mixtures (see Molecularsieves). For example, a Y-type 2eohte containing sodium and copper has been used to separate y -chlorotoluene from its isomers by selective absorption (65). The presence of ben2ylic impurities in chlorotoluenes is determined by standard methods for hydroly2able chlorine. Proton (66) and carbon-13 chemical shifts, characteristic in absorption bands, and principal mass spectral peaks are available along with sources of reference spectra (67). 

The refractive index of the sample can be written as a complex number 2 = n2 — ik2. At wavelengths where the sample is not absorbing, 2, the absorption constant, equals zero. However, kj is non-zero at wavelengths where the sample is absorbing. In transmission spectroscopy, the intensity of an absorption band depends almost entirely on k2 while in ATR the intensity of the same band is a complex function of 2 and 2- Nevertheless, the statement made previously still holds. There will be absorption bands in ATR at wavelengths where 2 0. Thus, bands are expected at the same wavelengths in transmission and in ATR but their intensities may be dissimilar. 

NMR and visible spectra have established that a number of S-N anions are present in such solutions.The primary reduction products are polysulfides Sx, which dissociate to polysulfur radical anions, especially the deep blue 83 ion (/Imax 620nm). In a IM solution the major S-N anion detected by NMR spectroscopy is cycZo-[S7N] with smaller amounts of the [SSNSS] ion and a trace of [SSNS]. The formation of the acyclic anion 5.23 from the decomposition of cyclo-Sjl is well established from chemical investigations (Section 5.4.3). The acyclic anions 5.22 and 5.23 have been detected by their characteristic visible and Raman spectra. It has also been suggested that a Raman band at 858 cm and a visible absorption band at 390 nm may be attributed to the [SaN] anion formed by cleavage of a S-S bond in [SSNS]. ° However, this anion cannot be obtained as a stable species when [SsN] is treated with one equivalent of PPhs. 

Table 29. IR absorption bands of Nb-O and Nb-F bond vibrations in the compounds MsNbiOjFl4 [115], Cs Nb202F9 and Rb7Nb404F 9 [198] (underlined numbers refer to highest intensity bands)...

A quick analysis of Equation (77) shows that if the melt layer is thin (kd 1), the emission spectrum corresponds to an absorption spectrum. This means that the emission peaks occur at the same wave numbers as the absorption bands. In case of thick melt layers (kd 1) Equation (77) becomes the following expression ... 

The UV-visible spectra of the H- and nifro-azobenzene dendrimers in chloroform solution showed strong absorption bands within the visible region due to the transitions of azobenzene chromophores (Table 2). Because of the stronger delocalization of n-electrons in nitro-azobenzene, the maximum absorption band is at a longer wavelength compared with that for H-azoben-zene. There was little spectral shift of the absorption maximum for dendrimers with different numbers of azobenzene units, indicating that dendrimers did not form any special intermolecular aggregates. 

Another very interesting result obtained from these FURS measurements is the difference between adsorbed CO obtained from dissolved CO and that from the dissociation of adsorbed methanol. The shift in wave number is more important with dissolved CO. These shifts may also be correlated with the superficial composition of the alloys, and it was observed that the optimized composition for the oxidation of CO (about 50 at.% Ru) is different from that for the oxidation of methanol (about 15 at.% Ru). FTIR spectra also revealed that the amount of adsorbed CO formed from methanol dissociation is considerably higher on R than on Pt-Ru. For a Ptog-Ru-o i alloy, the amount of linearly adsorbed CO is very small (Fig. 8), suggesting a low coverage in the poisoning species. Moreover, by observing the potentials at which the COj IR absorption band appears, it is possible to conclude that the oxidation of both (CHO)ads and (CO)acis species occurs at much lower potentials on a R-Ru alloy electrode than on pure Pt. 

Table 3 a number of spectral data on Cu(I) complexes. Figure 15 gives an example of a spectrum. These are all characterized by a broad absorption band in the ultraviolet or visible. Many of these show luminescence with a large Stokes shift and high quantum efficiency, even at room temperature. 

---