Absorbance, infrared spectroscopy

FIGURE 5.15 Fourier transform infrared spectroscopy absorbance spectra at different temperatures for a C22 monomeric stationary-phase. (Reproduced from Sander, L.C., et al., Anal. Chem.,55, 1068, 1983. With permission.)... 

Most infrared spectroscopy of complexes is carried out in tire mid-infrared, which is tire region in which tire monomers usually absorb infrared radiation. Van der Waals complexes can absorb mid-infrared radiation eitlier witli or without simultaneous excitation of intennolecular bending and stretching vibrations. The mid-infrared bands tliat contain tire most infonnation about intennolecular forces are combination bands, in which tire intennolecular vibrations are excited. Such spectra map out tire vibrational and rotational energy levels associated witli monomers in excited vibrational states and, tluis, provide infonnation on interaction potentials involving excited monomers, which may be slightly different from Arose for ground-state molecules. 

ATR infrared spectroscopy can be used to construct a depth profile showing the way in which the surface composition of a polymer changes as a function of distance away from the surface and into the polymer [3], As long as the polymer is not a very strong absorber, the absorbance of an infrared band in ATR is ... 

Infrared (IR) spectroscopy (Section 13.20) Analytical technique based on energy absorbed by a molecule as it vibrates by stretching and bending bonds. Infrared spectroscopy is useful for analyzing the functional groups in a molecule. 

Tests, The acid absorbs strongly in the infrared at i 739cm"1 and can be detd by infrared spectroscopy (Ref 7)... 

Recently, nonliving biomass of S. cucullata has been described as a low-cost absorbent of Cr(VI).106 Optimum conditions for the Cr(VI) adsorption by acid-treated S. cucullata were found out using a full factorial design. The Cr(VI) removal efficiency of the adsorbent was found to increase with the increase in time, temperature, adsorbate concentration, and stirring speed, and to decrease with increase in pH and adsorbent dose. The Fourier transform infrared spectroscopy (FT-IR) analysis revealed that in addition to electrostatic force, the adsorption may be due to... 

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 ... 

A combination of infrared spectroscopy with size exclusion chromatography has a wide application range in the characterization of copolymers, adhesives, impurity profiling in polymers and branching in polyolefines [60-65]. Commonly, the solvent used as a mobile phase absorbs strongly in the... 

The carbonyl index is not a standard technique, but is a widely used convenient measurement for comparing the relative extent and rate of oxidation in series of related polymer samples. The carbonyl index is determined using mid-infrared spectroscopy. The method is based on determining the absorbance ratio of a carbonyl (vC = 0) band generated as a consequence of oxidation normalised normally to the intensity of an absorption band in the polymer spectrum that is invariant with respect to polymer oxidation. (In an analogous manner, a hydroxyl index may be determined from a determination of the absorbance intensity of a vOH band normalised against an absorbance band that is invariant to the extent of oxidation.) In the text following, two examples of multi-technique studies of polymer oxidation will be discussed briefly each includes a measure of a carbonyl index. 

To evaluate the reactivity of model compounds III-VIII in photoinitiated cationic polymerization, we have employed real-time infrared spectroscopy (RTIR). Thin film samples of the model compounds containing 0.5 mol% of (4-n-octyloxyphenyl)phenyliodonium SbF - as a photoinitiator were irradiated in a FTIR spectrometer at a UV intensity of 20 mW/cm2. During irradiation, the decrease in the absorbance of the epoxy ether band at 860 cm-1 was monitored. 

Infrared spectroscopy is an excellent tool in iminoborane chemistry, which readily permits, to distinguish between iminoboranes and nitrile-borane adducts and to identify monomeric and dimeric forms of iminoboranes. This event is due to the fact that the i>CN of CN multiple bonds absorbs outside the fingerprint region and can be considered to be a valuable group frequency even when mixed with other vibrational modes. In some cases other vibrations like NH, BH, B-halogen or B-S stretching modes are helpful for determining the structure of iminoboranes. 

Several forms of infrared spectroscopy are in use, as illustrated in Fig. 8.4. The most common form of the technique is transmission infrared spectroscopy. In this case the sample consists typically of 10-100 mg of catalyst, pressed into a self-supporting disk of approximately 1 cm2 and a few tenths of a millimeter in thickness. Transmission IR can be applied if the bulk of the catalyst absorbs weakly. This is usually the... 

In this section, we shall look at the way these various absorptions are analysed by spectroscopists. There are four kinds of quantized energy translational, rotational, vibrational and electronic, so we anticipate four corresponding kinds of spectroscopy. When a photon is absorbed or generated, we must conserve the total angular momentum in the overall process. So we must start by looking at some of the rules that allow for intense UV-visible bands (caused by electronic motion), then look at infrared spectroscopy (which follows vibrational motion) and finally microwave spectroscopy (which looks at rotation). 

---