Absolute infrared intensities

McMahon s group reported room temperature ZTRID values for dissociation of a number of cluster ions. Particularly interesting for thermochemical analysis are recent measurements of the temperature dependence of several reactions, because the temperature dependence is directly related to the dissociation energy. A further promising development is the ab initio calculation of the absolute infrared intensities for the vibrational modes of two of these complexes, which allows an independent derivation of from the data. For one of the complexes, (H20)3Cr,... 

The C coefficients are obtained from the vibrational wave functions calculated as described above the measured relative dipole moments are listed in table 8.19 and the absolute infrared intensity measurements [108] are given in table 8.20. 

Pine, A. S. and Howard, B. J., Hydrogen bond energies of the HF and HCl dimers from absolute infrared intensities, J, Chem. Phys. 84, 590-596 (1986). 

The dipole moment components as a function of time are usually computed with a fixed charge approximation. Values of atomic charges are often taken from quantum chemical calculations of representative models, although absolute charge values play no role (other than influencing the MD trajectory) unless absolute infrared intensities are to be computed. FFowever, the relative values of charges are of importance for reproducing relative band intensities. 

Rogers, J. D. and Stephens, R. D. (1988). Absolute Infrared Intensities for F-113 and F-114 and an Assessment of Their Greenhouse Warming Potential Relative to Other Chlorofluorocar-bons. J. Geophys. Res. 93(D3), 2423-2428. 

The theoretical conclusion from the comparison of these structures is that the Si-Si bond distances increase in the order 19 >20 >18, while the experimental order (of substituted derivatives) is 18>19>20. The discrepancy has been attributed109 to the presence of bulky substituents in the experimentally determined smaller rings108a,b. Grev and Schaefer have also calculated the vibrational frequencies and the absolute infrared intensities of the compounds109. 

The absolute infrared intensities of the two translational lattice mode lines at 49 and 70 cm i were calculated by Ron and Schnepp (1967) using the quadrupole-induced theory of Schnepp (1967),These authors made crude estimates of the observed intensities and found them to be of the... 

David and Person (1968) measured the absolute infrared intensities of the translational lattice modes of the solid halogens. They did not carry out a complete calculation adapted to the crystal structure of these solids. These authors found, however, very good correlation between the measured absolute intensities and the molecular properties, i.e., quadrupole moments and polarizabilities, as expected from the theory. 

Friedrich (1970) has measured the absolute infrared intensities of the two optic librational modes of the solids of CICN and BrCN. He also calculated the intrinsic intensities of these modes using a dipolar coupling theory referred to in Section IVB.2. Good agreement was obtained between calculated and measured values. It was found that the local field correction [Eq. (4.22)] causes an increase of about 100% in the theoretical intensities for these substances, whereas the Lorentz effective field correction gave rise to an increase of less than 50%. The samples were prepared by deposition of gas on a cold window and the sample thicknesses were measured by an interference fringe technique. 

Friedrich (1967) measured the absolute infrared intensities of the librational mode of OCS crystal. In his calculation, he introduced an effective field correction factor, which had been determined by other authors by fitting to the observed infrared intensity of the intramolecular bending mode in the solid. Agreement between measured and calculated intensities was then excellent. 

Because of the lowering of molecular symmetry, the inversion center is lost and the most relevant Raman lines (fl mode) become active in the infrared spectrum (see Fig. 28.15). The values of the absolute infrared intensities of fl modes are very large, even two orders of magnitude larger than the values usually measured in infrared intensity spectroscopy. 

The great chemical stability of polyalkoxylhiophenes has initiated a systematic experimental spectroscopic study of the charge injection by the oxygen atom into the thiophene ring. The absolute infrared intensity of... 

Cartesian reference systems, geometric parameters and symmetiy coordinates for H2O and NH3 are given in Chapter 3. Dipole moment derivatives with respect to symmetiy coordinates for H2O, evaluated in analyzing experimental absolute infrared intensities, are also presented there. dp/dSj dipole moment derivatives for ammonia used in the present calculations were taken from Ref. [147] and are presented in Table 4.13. The signs of these quantities have been fixed with the aid of ab initio MO calculations [147]. Elements of the respective matrices for both molecules were evaluated by employing the heavy isotope mediod [34], weighting the respective heavy atoms by a factor of 1000. The rotational correction terms for ammonia are tabulated in Table 3.3. The Rs matrix for H2O has the following form (in D A l or D rad )... 

The paramount difficulties in the experimental determination of accurate absolute infrared intensities and differential Raman scattering cross sections seem, however, to persist in the theoretical evaluation of these quantities as well. As we will see, predicted Raman intensities appear to be more consistent with experiment as compared to infrared intensities. 

Similar results are obtained for the absolute infrared intensities F.. 

How does the advent of F.T.I.R. spectroscopy change this picture Rather little work has as yet been published on the measurement of absolute infrared intensities by F.T. methods, although the ability of the technique to accurately and rapidly handle spectral subtractions is a major aspect of most of its... 

A useful comparison of F.T. and conventional I.R. instrumentation has been given by Chenery and Sheppard.The advantages of the former - which have yet to be fully exploited in the field of absolute infrared intensities are ... 

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