Near infrared absorption frequencies

Table 7.24 Absorption Frequencies of Other Double Bonds Table 7.25 Absorption Frequencies of Aromatic Bands Table 7.26 Absorption Frequencies of Miscellaneous Bands Table 7.27 Absorption Frequencies in the Near Infrared Table 7.28 Infrared Transmitting Materials...

TABLE 7.27 Absorption Frequencies in the Near Infrared Values in parentheses are molar absorptivity. 

In Welsh s first study [128], the shape of the absorption profile was found to be independent of the density of the gas if normalized by density squared, a(v)/n2, at nearly all frequencies v. Pair spectra show no variation with density other than the density squared relationship - up to the point where ternary (or higher-order) spectra affect the measurements (if monomers are infrared inactive in the spectral band considered). 

Very few experiments have been performed on vibrational dynamics in supercritical fluids (47). A few spectral line experiments, both Raman and infrared, have been conducted (48-58). While some studies show nothing unique occurring near the critical point (48,51,53), other work finds anomalous behavior, such as significant line broadening in the vicinity of the critical point (52,54-60). Troe and coworkers examined the excited electronic state vibrational relaxation of azulene in supercritical ethane and propane (61-64). Relaxation rates of azulene in propane along a near-critical isotherm show the three-region dependence on density, as does the shift in the electronic absorption frequency. Their relaxation experiments in supercritical carbon dioxide, xenon, and ethane were done farther from the critical point, and the three-region behavior was not observed. The measured density dependence of vibrational relaxation in these fluids was... 

In the near and the mid infrared, the absorption of light by matter originates from the interaction between the radiation from a light source and the chemical bonds of the sample. More precisely, if the atoms situated at the two extremes of a bond are different, they form an electric dipole that oscillates with a specific frequency. If such a non-symmetrical bond is irradiated by a monochromatic light source whose frequency is the same as the dipole, then an interaction will occur with the bond. Thus, the electrical component of the wave can transfer its energy to the bond on condition that the mechanical frequency of the bond and the electromagnetic frequency of the radiation are the same (Figure 10.1). This simplified approach can be used to rationalize that in the absence of a permanent... 

The near-constant absorption frequency of a particular bond or group is used to advantage to check for the presence or absence of certain bonds in a new compound or to follow the progress of a reaction—for example, to determine the presence and type, or absence, of C-H vibrations. Later in this chapter a general procedure for the qualitative interpretation of infrared spectra will be outlined. 

Finally, as shown in Figure 6-24a, the less ener-getic near- and mid-infrared radiation can bring about transitions only among the k vibrational levels of the ground state. Here, k potential absorption frequencies are given by k equations, which may be formulated as... 

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