Far-infrared spectral regions

The C—C bond was found to be slightly more perturbed than in the monolithium species (i.e., LiC2H4) and the Li—C interactions somewhat more rigid. The normal coordinate analysis showed that such a model is capable of satisfactorily reproducing the measured isotopic shifts on the observed 12 fundamentals. However, the very important Li—Li vibration, which could prove the proposed geometry, was not detected in the expected far-infrared spectral region ... 

Thermal emission spectroscopy can be used in middle- and far-infrared spectral regions to make stratospheric measurements, and it has been applied to a number of important molecules with balloon-borne and satellite-based detection systems. In this approach, the molecules of interest are promoted to excited states through collisions with other molecules. The return to the ground state is accompanied by the release of a photon with energy equal to the difference between the quantum states of the molecule. Therefore, the emission spectrum is characteristic of a given molecule. Calculation of the concentration can be complicated because the emission may have originated from a number of stratospheric altitudes, and this situation may necessitate the use of computer-based inversion techniques (24-27) to retrieve a concentration profile. 

Raman spectroscopy can offer vibrational information that is complementary to that obtained by IR. Furthermore, since the Raman spectrum reveals the backbone structure of a molecular entity [55], it is particularly useful in the examination of polymer film-coated electrodes. There are also some distinct advantages over in situ IR. For example, both the mid and far infrared spectral regions can be accessed with the same instrumental setup (in IR spectroscopy, these two regions typically require separate optics) [55]. Second, solvents such as water and acetonitrile are weak Raman scatterers thus the solvent medium does not optically obscure the electrode surface as it does in an in situ IR experiment. 

Passive remote sounding instruments for both the mm-wave and sub-mm or far-infrared spectral regions have been developed for atmospheric remote sounding. Some examples are briefly described below. 

Lattice dimerization in the course of the spin-Peierls-like transition leads to the appearance of new optically active modes folded from a boundary of the Brillouin zone to its center. Charge ordering results in a dielectric anomaly observable in the far-infrared spectral region. 

The analysis of the dynamics and dielectric relaxation is made by means of the collective dipole time-correlation function (t) = (M(/).M(0)> /( M(0) 2), from which one can obtain the far-infrared spectrum by a Fourier-Laplace transformation and the main dielectric relaxation time by fitting < >(/) by exponential or multi-exponentials in the long-time rotational-diffusion regime. Results for (t) and the corresponding frequency-dependent absorption coefficient, A" = ilf < >(/) cos (cot)dt are shown in Figure 16-6 for several simulated states. The main spectra capture essentially the microwave region whereas the insert shows the far-infrared spectral region. 

List the upper and lower limits of the near-, mid-, and far-infrared spectral regions in... 

In the far-infrared spectral region water vapour can absorb radiation by transition between different rotational levels without any vibrational or electronic changes. Such a pure rotational spectrum can only be exhibited by a molecule with a permanent dipole moment. The rotational spectrum has been measured for wavelengths up to 2 mm(Herzberg, 1945, p. 58 Furashov, 1966), where this type of absorption ceases and, in good agreement with theory, consists of relatively sharp lines distributed in what looks... 

A bibliography of approximately 500 papers concerning the far-infrared spectral region was published in the December 1960 Journal of the Optical Society of America by Palik [ ]. He summarized this body of work as follows ... 

---