Point dipole model

The quality of the results that can be obtained with point charge or dipole models depends critically on the input solvation shell structure. In view of the computer power available today, taking the most rigorous route... 

It is generally thought that the ER effect happens only in nonconducting oils. Here an ER effect in solid-like matrices such as polymer gels will be discussed. The nature of the ER effect in polymer gels will be explained using the point dipole model in [44],... 

Polarization in the point dipole model occurs not at the surface of the particle but within it. If dipoles form in particles, an interaction between dipoles occurs more or less even if they are in a solid-like matrix [48], The interaction becomes strong as the dipoles come close to each other. When the particles contact each other along the applied electric field, the interaction reaches a maximum. A balance between the particle interaction and the elastic modulus of the solid matrix is important for the ER effect to transpire. If the elastic modulus of the solid-like matrix is larger than the sum of the interactions of the particles, the ER effect may not be observed macroscopically. Therefore, the matrix should be a soft material such as gels or elastomers to produce the ER effect. 

Since the unpaired electron in transition metal complexes is generally localized near the central ion and the ligand atoms in the first coordination sphere, summation in (5.5) over these nuclei is often sufficient. In this approximated form, the point-dipole model has frequently been applied in ENDOR studies of transition metal complexes to determine the proton positions from their hfs tensors (Sect. 6). In some cases the accuracy of this method has turned out to be significantly higher than that of an X-ray diffraction analysis62,130 131). 

In the present review the diverse notations used by different authors will be retained. For example Ciampolini et al. (7, 8, 12) for a point-dipole model initially used the parameters fx, and where / = effective Hgand-dipole of the ligand, Bn = , and R= metal-... 

For line shape calculations, purely exponential dipole models, and exponential models combined with a dispersion term, Dn/R 1, have been used, see Chapter 4 for details. The variation of the line shape with these dipole models has been studied. In all cases, the purely exponential dipole model gives inferior results when compared with the exp-7 models the influence of the dispersion term, while small, is nevertheless significant in line shape analyses moment analyses, in contrast, have reportedly not been able to demonstrate the significance of the dispersion term. It would seem that the accuracy of quantum line shape calculations of the absorption by rare gas pairs has reached the point where further progress must await more accurate experiments at low gas densities and over a wider range of frequencies and temperatures. 

In summary, the point dipole model with images can be made to account for the experimentally determined effects of intermole-cular dipole coupling. The magnitudes of the effects cannot be predicted from the properties of the free CO molecule but they can be used to estimate the changed values in the chemisorbed state. 

While the clathrate model is attractive, it is not correct to assume that the water is organized in some long-lived structure the observation that the self-diffusion coefficient for co-sphere water is larger than that for the solute rules this out. However, the rotational correlation time is shorter for ethanol and t-butyl alcohol in water (in the clathrate cage ) than in the pure liquid (Goldammer and Hertz, 1970 Goldammer and Zeidler, 1969). Nmr experiments show that in water the solvent dipole moments point away from the apolar groups (Hertz and Radle, 1973). 

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