Vibrational infrared region

Most chemists refer to the radiation in the vibrational infrared region of the electromagnetic spectmm in terms of a unit called a wavenumber (v), rather than wavelength (/i or /im). Wavenumbers are expressed as reciprocal centimeters (cm ) and are easily computed by taking the reciprocal of... 

In organic chemistry, we use a portion of the electromagnetic spectrum called the vibrational infrared region. This region extends from 2.5 X 10 to 25 X 10 m and corresponds to energies from 48-4.8 kj/mol (11—1.2 kcal/mol). We commonly refer to radiation in the vibrational infrared region by its wavenumber (v), the number of waves per centimeter ... 

Fingerprint region The portion of the vibrational infrared region that extends from 1000 to 400 cm and that is unique to every compound. 

The vibrational infrared region, which extends from 2.5 X 10" to 2.5 X 10 m... 

Radiation in the vibrational infrared region is commonly referred to by its frequency in wavenumbers, or the number of waves per centimeter (cm read reciprocal centimeters). 

The range of photon energies (160 to 0.12 kJ/mol (38-0.03 kcal/mol)) within the infrared region corresponds to the energies of vibrational and rotational transitions of individual molecules, of electronic transitions in many semiconductors, and of vibrational transitions in crystalline lattices. Semiconductor electronics and crystal lattice transitions are beyond the scope of this article. 

Stretching vibration in the infrared region. The imine salts possess an active hydrogen, whereas their quaternization products exhibit the same spectral properties as the enamine salts (187). 

Matrix Raman spectroscopy allows detection of some additional vibrations which are inactive in IR spectra (e.g. symmetrical vibrations vi in AB3 molecules having 3 symmetry) or which tie in the far infrared region. In practice, matrix-isolated organic intermediates have not been studied by Raman spectroscopy the main objects of these investigations are inorganic molecules (AICI3, PbS, Gep2, SiO, etc.) which are evaporated from solids in effusion cells. 

In SFG vibrational spectroscopy, cOi is usually fixed in the visible region and CO2 is scanned in the infrared region. In the most widely used geometry, the two laser... 

It is the mid-infrared region that is used for the study of molecular vibrations and is therefore of greatest importance in the present context. The first studies in the mid-IR on catalysis were by Eischens and Pliskin (1958) whose review is still a standard work of reference. 

Obviously, a great deal more information could be obtained if the isomeric ions could be probed spectroscopically. Vibrational states of the various isomers are not generally well known, but some structural information is available. Thus, the rotational structure of vibrational transitions may provide a better signature for particular isomers. Certainly, insufficient data are available about the potential surfaces of electronically excited states for electronic excitation to be used as a probe, e.g., as in the very sensitive laser induced fluorescence. At present, there are sensitivity limitations in the infrared region of the spectrum, but this may well be an avenue for the future. The study of isomeric systems and their potential surfaces has just begun ... 

In 1990 we showed that ethenedithione (115) is a stable molecule under matrix conditions. It can be prepared by photolysis of the matrix-isolated precursors 113, 114, and 116.143 Different pathways to 115 have been found by Wentrup et al.144 The matrix IR spectrum of 115 shows one absorption corresponding to the only IR active stretching mode. The IR active bending vibration is expected to appear in the for us unobservable far infrared region. The position of both IR inactive stretching vibrations were derived from two observed combination bands. The IR spectra allow no decision about the multiplicity of 115, since calculations show, that the equilibrium geometries of both states are almost identical. Recent calculations121 145 favor the triplet state. 

Absorption of electromagnetic radiation in the infrared region of the spectrum resulting in changes in the vibrational energy of molecules. 

Absorption of radiation in the infrared region of the electromagnetic spectrum results in changes in the vibrational energy of molecules. Energy changes are typically 6 x 103 to 42 x 103J mol-1, which corresponds to 250-... 

Infrared spectroscopy is the most common form of vibrational spectroscopy. Infrared radiation falls into three categories, as indicated in Table 8.1. It is the mid-infrared region that is of interest to us. 

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