Vibrational spectroscopy group frequencies

Molecular vibrations are the basis of infrared (IR) spectroscopy Certain groups of atoms vibrate at characteristic frequencies and these frequencies can be used to detect the pres ence of these groups in a molecule... 

The interactions of photons with molecules are described by molecular cross-sections. For IR spectroscopy the cross-section is some two orders of magnitude smaller with respect to UV or fluorescence spectroscopy but about 10 orders of magnitude bigger than for Raman scattering. The peaks in IR spectra represent the excitation of vibrational modes of the molecules in the sample and thus are associated with the various chemical bonds and functional groups present in the molecules. The frequencies of the characteristic absorption bands lie within a relatively narrow range, almost independent of the composition of the rest of the molecule. The relative constancy of these group frequencies allows determination of the characteristic... 

The frequencies of absorption bands present gives diagnostic information on the nature of functional groups in materials as well as information from any observed frequency shifts on aspects such as hydrogen bonding and crystallinity. In many cases, spectra can be recorded non-destructively using either reflection or transmission procedures. IR spectra of small samples can also be obtained through microscopes (IR microspectrometry). Chalmers and Dent [8] discuss the theory and practice of IR spectroscopy in their book on industrial analysis with vibrational spectroscopy. Standard spectra of additives for polymeric materials include the major collection by Hummel and Scholl [9]. 

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. 

The presence of group frequencies or "finger print" regions in infrared spectra make vibrational spectroscopy a key analytical method in identifying classes of molecules. 

One of the great advantages of vibrational spectroscopy is that many hydrocarbon groupings, such as CH3, CH2, C=C, C=C, etc., have characteristic vibration frequencies/wavenumbers, many of which fall in the wavenumber ranges transmitted by oxide supports. Furthermore, for use in connection with... 

The most basic information that is needed for constructing a global potential energy surface for gas phase MD simulations is the structures and vibrational frequencies. The earliest information about gas-phase RDX molecular structures was obtained from theoretical calculations [54-58]. In 1984 Karpowicz and Brill [59] reported Fourier transform infrared spectra for vapor-phase (and for the a - and p -phase) RDX in 1984, however, their data precluded a complete description of the molecular conformations and vibrational spectroscopy. More recently, Shishkov et al. [60] presented a more complete description based on electron-scattering data and molecular modeling. They concluded that the data were best reproduced by RDX in the chair conformation with all the nitro groups in axial positions. 

In vibrational studies (IR/Raman, see Infrared Spectroscopy and Raman Spectroscopy), characteristic frequencies for Au bonds have been compiled, which are useful for suggestions regarding molecular synunetries and structures and to calculate force constants for the Au bonds. The values have been tabulated in handbooks, and they show consistent results for the individual groups of compounds. Moreover,... 

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