Infrared spectroscopy overtone bands

The insoluble material is assumed to be the graft copolymer and this is verified by infrared spectroscopy. For grafting onto the butadiene portion of a copolymer, the C-H out-of-plane bending vibrations as well as the olefin C-H stretching vibration are most useful. The graft copolymer of acrylonitrile onto polystyrene cannot be analyzed by infrared spectroscopy since the only change would be in the C-H overtone region and these bands are too weak to permit interpretation. 

Although the Fourier compression method can be effective for reducing data into frequency components, it cannot effectively handle situations where the dominant frequency components vary as a function of position in the spectrum. For example, in Fourier transform near-infrared (FTNIR) spectroscopy, where wavenumber (cm-1) is used as the x-axis, the bandwidths of the combination bands at the lower wavenumbers can be much smaller than the bandwidths of the overtone bands at the higher wavenumbers.31,32 In any such case where relevant spectral information can exist at different frequencies for different positions, it can be advantageous to use a compression technique that compresses based on frequency but still preserves some position information. The Wavelet transform is one such technique.33... 

Raman Selection Rules. For polyatomic molecules a number of Stokes Raman bands are observed, each corresponding to an allowed transition between two vibrational energy levels of the molecule. (An allowed transition is one for which the intensity is not uniquely zero owing to symmetry.) As in the case of infrared spectroscopy (see Exp. 38), only the fundamental transitions (corresponding to frequencies v, V2, v, ...) are usually intense enough to be observed, although weak overtone and combination Raman bands are sometimes detected. For molecules with appreciable symmetry, some fundamental transitions may be absent in the Raman and/or infrared spectra. The essential requirement is that the transition moment F (whose square determines the intensity) be nonzero i.e.. 

Compared to the measurement of VCD the measurement of optical activity in the Raman spectrum offers all the well known advantages that Raman spectroscopy has over infrared spectroscopy the use of the inexpensive glass as the sample cell, and the occu-rance of fewer bands, overtones and combination bands are reduced in intensity, thereby diminishing the possibility of overlap. Very important also is the fact that water is usable as solvent. 

Hydroxyaryl)-3-hydroxyindolones Inductive effects 102 Infrared polarization spectroscopy 368 Infrared spectroscopy 367-386 density functional theory and 368 hydrogen bonding and 368, 370, 371, 375-386 in analysis 997 hnear dichroism (LD) 368 near-, overtone and combination bands in 371... 

The vibration of the X—H group is large in amplitude because of the low atomic weight of hydrogen, and consequently, deviates appreciably from true harmonic motion. The overtone and combination bands are therefore relatively intense. The phenomena most studied with near-infrared spectroscopy have been intermolecular associations, the type most familiar to biochemists being hydrogen bonding. 

The ideas fundamental to an understanding of infrared spectroscopy were introduced in this chapter. The electromagnetic spectrum was considered in terms of various atomic and molecular processes and classical and quantum ideas were introduced. The vibrations of molecules and how they produce infrared spectra were then examined. The various factors that are responsible for the position and intensity of infrared modes were described. Factors such as combination and overtone bands, Fermi resonance, coupling and vibration-rotation bands can lead to changes in infrared spectra. An appreciation of these issues is important when... 

Near-infrared (NIR) spectroscopy is also an excellent tool for examining plant tissue. As in the mid-infrared region, plants produce bands in the NIR region due to the presence of carbohydrates. The latter exhibit overlapped combination and overtone bands of the 0-H and C-H groups. Multivariate analysis of the near-infrared spectra of different plant species can be used to differentiate samples [54]. 

Near-infrared spectroscopy proved valuable for fhe analysis of pharmaceutical powders in a 1981 paper by Becconsall et al. [119]. Near-infrared and UV phofoacoustic spectroscopy were used for determination of propranolol-magnesium carbonate mixtures. Spectra were collected from 1300 to 2600 nm with carbon black as the reference. An aromatic C-H combination band at 2200 nm and an overtone band at 1720 nm were used to quantify propranolol. In this case, the UV data were nonlinear, while the NIR method provided a linear calibration. 

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