Polarization dipolar

The first moments or dipolar polarization components of the charge distribution are defined by three-dimensional integrals for a given basin 2 according to ... 

It is important to understand that the atomic charges refer to atoms that are not spherical. Consequently the centroid of electronic charge of an atom does not in general coincide with the nucleus, and each atom therefore has an electric dipole moment—or, more generally, an electric dipolar polarization (since only the dipole moment of electrically neutral atoms is origin independent). 

The total dipole moment of a molecule is the resultant of the vector sum of the atomic dipolar polarization ( a.lp) of all the atoms in the molecule and of all the charge transfer dipoles arising from the transfer of charge between bonded... 

Thermal effects (dielectric heating) can result from dipolar polarization as a consequence of dipole-dipole interactions of polar molecules with the electromagnetic field. They originate in dissipation of energy as heat, as an outcome of agitation and intermolecular friction of molecules when dipoles change their mutual orientation at each alternation of the electric field at a very high frequency (v = 2450 MHz) [10, 11] (Scheme 3.1). 

A decrease in the activation energy AG is certainly a major effect. Because of the contribution of enthalpy and entropy to the value of AG (= AH -TAS ), it might be predicted that the magnitude of the -TAS term would increase in a microwave-induced reaction, because organization is greater than with classical heating, as a consequence of dipolar polarization. 

Microwave effects result from material-wave interactions and, because of the dipolar polarization phenomenon, the greater the polarity of a molecule (such as the solvent) the more pronounced the microwave effect when the rise in temperature [43] is considered. In terms of reactivity and kinetics the specific effect has therefore to be considered according to the reaction mechanism and, particularly, with regard to how the... 

Dipolar ion, reaction with solvents, 17 782 Dipolar polarization, 10 21 Dipole-dipole interactions, 15 103 23 91-92 in water, 26 16... 

Microwave radiation, as all radiation of an electromagnetic nature, consists of two components, i.e. magnetic and electric field components (Fig. 1.3). The electric field component is responsible for dielectric heating mechanism since it can cause molecular motion either by migration of ionic species (conduction mechanism) or rotation of dipolar species (dipolar polarization mechanism). In a microwave field, the electric field component oscillates very quickly (at 2.45 GHz the field oscillates 4.9 x 109 times per second), and the strong agitation, provided by cyclic reorientation of molecules, can result in an... 

MAOS is mainly based on the efficient heating of materials by the microwave dielectric heating effect [15] mediated by dipolar polarization and ionic conduction. When irradiated at microwave frequencies, the dipoles (e.g., the polar solvent... 

Fig. 2.38 Variation of e and with frequency. Space charge and dipolar polarizations are relaxation processes and are strongly temperature dependent ionic and electronic polarizations are resonance processes and sensibly temperature independent. Over critical frequency ranges energy dissipation is a maximum as shown by peaks in ...

The dipolar polarization mechanism is present in substances containing molecules with permanent dipole moments. In these compounds, the bulk material is neutral, since normally the orientation of the polar molecules constituting the material is randomly distributed due to the action of thermal energy. In this situation, under the influence of the electric field, the dipoles will be partially oriented in the direction of the electric field. The dipole moment can be written as... 

In the frame of the Debye model, the dipolar polarization decay is given by... 

Molecular dipolar polarization was difficult to define from dielectric measurements. A large first dispersion in time for isothermal cures of Resin 5208 is attributed to charge migration in a viscous medium. High values of dielectric constant and dielectric loss factor are attributed to the formation of an ion double-layer and sample conductivity, respectively. Limited frequency data on a smaller second dispersion prevent unequivocal assignment of its relationship to molecular changes. 

The first moment provides a measure of the extent and direction of the dipolar polarization of the atom s charge density by determining the displacement of the atom s centroid of negative charge from the position of its nucleus. The dipole moment of a neutral molecule is expressed as... 

Unlike the polarization of the base atom in a regular hydrogen bond interaction, the dipolar polarization of a noble gas atom is towards the hydrogen. In the relatively weak complex of HF with N2, the change in the polarization of the base N away from H is very small. This interaction is transitional between the two patterns of atomic polarizations that result from the mutual penetration of closed-shell systems with little or no accompanying charge transfer, the features common to van der Waals and hydrogen-bonded interactions. 

In addition to the dipolar polarization term, a significant heating effect may also result from resistive heating, as charge carriers are displaced under the influence of the field. This term is significant in solid conductors such as some forms of carbon, and aqueous electrolyte solutions where ionic conduction gives rise to a heating effect comparable to that from dipolar loss terms. 

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