Solvent electrostatic configuration

Figure 7-14. Comparison between the statistical distribution and the average value obtained using the average solvent electrostatic configuration (central vertical line)...

According with experimental data, the n-n band of MOx is shifted by —2,145 90 cm (—0.266 0.011 eV) when the solvent changes from iso-octane to water [16] and extrapolated as —2,410 90 cm (—0.299 0.011 eV) from gas phase to water using a linear regression in the a plot of the experimental values for the maximum absorption transition energy, Emax. of the MOx in several solvent [16] versus the normalized Reichardt solvent polarity scale, Ej [2] (see Fig. 3). In order to discuss, the absorption spectrum of solute MOx (S) in water different theoretical representations of the solvent was adopted (1) the polarizable continuum model (S -I- PCM), which provides a simplified representation of the solvent as a continuum dielectric medium (2) the average solvent electrostatic configuration (S -I- ASEC), where 250 water molecules of... 

ASEP/MD, acronym for average solvent electrostatic potential obtained from molecular dynamics data, is a sequential QM/MM method that makes extensive use of the mean field approximation (MFA) [24], In solution, any static property A of the system must be calculated by averaging over the configurational space A defined by all the configurations thermally accessible to the system ... 

Tacticity of products. Most solid catalysts produce isotactic products. This is probably because of the highly orienting effect of the solid surface, as noted in item (1). The preferred isotactic configuration produced at these surfaces is largely governed by steric and electrostatic interactions between the monomer and the ligands of the transition metal. Syndiotacticity is mostly produced by soluble catalysts. Syndiotactic polymerizations are carried out at low temperatures, and even the catalyst must be prepared at low temperatures otherwise specificity is lost. With polar monomers syndiotacticity is also promoted by polar reaction media. Apparently the polar solvent molecules compete with monomer for coordination sites, and thus indicate more loosely coordinated reactive species. 

Theoretical studies of the role of polymer additives lag behind their analogs in electrostatic stability since polymer molecules have considerably more configurational freedom and since the interaction of the polymer molecules with the solvent is an inseparable part of phenomena in polymer-colloid mixtures. We begin with some of the general issues and a thermodynamic analysis of the role of polymer on stability in Section 13.5. 

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