Electrostatic interaction, molecular theories

Color from Transition-Metal Compounds and Impurities. The energy levels of the excited states of the unpaked electrons of transition-metal ions in crystals are controlled by the field of the surrounding cations or cationic groups. Erom a purely ionic point of view, this is explained by the electrostatic interactions of crystal field theory ligand field theory is a more advanced approach also incorporating molecular orbital concepts. 

The ions are regarded as rigid balls moving in a liquid bath. It is assumed that the macroscopic laws of motion in a viscous medium hold, and that the electrostatic interaction is determined by the theory of continuous dielectrics. This assumption implies that the moving particles are large compared to the molecular structure of the liquid. The most successful results of continuous theories can be found in any textbook of physical chemistry Stokes , law for viscous motion, Einstein s derivation of the dependence of viscosity on the concentration... 

In Equations 2.17-2.19, the Boltzmann factor contains contributions arising from the different interactions considered by the molecular theory. For example, 7t(z) and /(z) represent the repulsive and electrostatic interaction fields at z. It should be stressed that these fields are unknowns for the theory and that they depend on the distribution of all the different species across the film, that is. Equations 2.17-2.19. This has two consequences. First, a self-consistent solving process must be used, which means that simplicity is sacrificed in the theory in order to study the system in all its molecular complexity. Second, their interactions in the system are highly coupled and nonlocal [157]. 

The structural interpretation of dielectric relaxation is a difficult problem in statistical thermodynamics. It can for many materials be approached by considering dipoles of molecular size whose orientation or magnitude fluctuates spontaneously, in thermal motion. The dielectric constant of the material as a whole is arrived at by way of these fluctuations but the theory is very difficult because of the electrostatic interaction between dipoles. In some ionic crystals the analysis in terms of dipoles is less fruitful than an analysis in terms of thermal vibrations. This also is a theoretically difficult task forming part of lattice dynamics. In still other materials relaxation is due to electrical conduction over paths of limited length. Here dielectric relaxation borders on semiconductor physics. 

The nature of the bonds forming molecular addition compounds has been investigated by several workers, but up to now it has not been made sufficiently clear. Pfeiffer [112] held that complex formation was due to the mutual saturation of residual valencies , but Briegleb [113,114] advanced the theory that addition compounds should be regarded as polarization aggregates which owed their stability to electrostatic interactions, possibly due to polarization of one component by the other. Thus, in the case of polynitro compounds, their strongly polar mole cules influence the non polar molecules of the hydrocarbon. Further, no covalent bonds exist between these two kinds of molecules. This hypothesis has received considerable support and a new development. 

The DLVO-theory considers only the molecular van der Waals and electrostatic interactions. A complete analysis of the theory can be found in several monographs [e.g. 3-6] where original and summarised data about the different components of disjoining pressure in thin liquid films, including in foam films are compiled. 

Hence, the experimental isotherms of films from NaDoS cannot be explained with the DLVO-theory. The above analysis reveals that the reason for the deviations is not connected to the restrictions of the theory of molecular forces but to the theory of electrostatic interactions of double electric layers, especially at high surface charge and potential values. Another way to explain the deviations from the DLVO-theory is the expression of the structural interactions forces in spite of the fact that the scope of their actions appears to be very large. 

Silicon-organic interactions, where silicon is present as solid silica and as a dissolved species in aqueous solution, are examined using classical electrostatic and solvation theory, crystal chemistry, thermodynamics, and ab initio molecular orbital calculations. Specifically, I address why various silica polymorphs and other oxides interact... 

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