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Permittivity effects, polar molecule dielectric

From Maxwell s theory of electromagnetic waves it follows that the relative permittivity of a material is equal to the square of its refractive index measured at the same frequency. Refractive index given by Table 1.2 is measured at the frequency of the D line of sodium. Thus it gives the proportion of (electronic) polarizability still effective at very high frequencies (optical frequencies) compared with polarizability at very low frequencies given by the dielectric constant. It can be seen from Table 1.2 that the dielectric constant is equal to the square of the refractive index for apolar molecules whereas for polar molecules the difference is mainly because of the permanent dipole. In the following discussion the Clausius-Mossoti equation will be used to define supplementary terms justifying the difference between the dielectric constant and the square of the refractive index (Eq. (29) The Debye model). [Pg.10]

The temperature dependence of the dielectric constant of polar molecules also differs from that of nonpolar molecules. Change of temperature has a small effect only for nonpolar molecules (change of density). For polar molecules, the orientation polarization falls off rapidly with increasing temperature, because thermal motion reduces the alignment of the permanent dipoles by the electric field. In the following discussion we will see that it is possible to have increasing values of dielectric permittivity with increasing temperature. [Pg.10]

The FIR response (0.1 cm to 100 cm ) of polar dielectrics is related to inertial effects and the libration of dipoles Ions in polar media contribute in a complex manner. Information is provided by Lambert-Beer s law related to the complex relative permittivity containing the conductance contribution to e" when electrolyte solutions are investigated. The rotational motion of polar molecules gives rise to a broad-band absorption with a maximum in the FIR region . Models proposing the libration of each molecule in the cage of its neighbours are used to explain the excess absorption observed 294,332,333) solution interact specifically. [Pg.72]

D18.3 Dipole moments are not measured directly, but are calculated from a measurement of the relative permittivity, (dielectric constant) of the medium. Equation 18.IS implies that the dipole moment can be determined from a measurement of function of temperature. This approach is illustrated in Example 18.2. In another method, the relative permittivity of a solution of the polar molecule is measured as a function of concentration. The calculation is again based on the Debye equation, but in a modified form. The values obtained by this method are accurate only to about 10%. See the references listed under Furiher reading for the details of this approach. A third method is based on the relation between relative permittivity and refractive index, eqn 18.17, and thus reduces to a measurement of the refractive index. Accurate values of the dipole moments of gaseous molecules can be obtained from the Stark effect in their microwave spectra. [Pg.357]

The origin of the effect here represented by x0) can be derived from modelistic considerations. Solvent molecules are mobile entities and their contribution to the dielectric response is a combination of different effects in particular the orientation of the molecule under the influence of the field, changes in its internal geometry and its vibrational response, and electronic polarization. With static fields of moderate intensity all the cited effects contribute to give a linear response, summarized by the constant value e of the permittivity. This molecular description of the dielectric response of a liquid is... [Pg.10]

The rate of displacing atoms and electrons within a molecule corresponds to optical frequencies, and hence no dielectric dispersion of Mm is normally encountered in or below the microwave range (v < 10 GHz). Since all other polarization effects are not that fast, the polarizabilities a, determine exclusively the electric permittivity at optical frequencies, eop. Thus at sufficiently high frequencies the relations (12) and (13) may be combined with (1) to evaluate a,. For the pure species s consisting of isotropic spherical molecules, a, can be given by the refractive index n, if Maxwell s relation... [Pg.93]

The dielectric constant (relative permittivity) is a macroscopic property. If molecules 1 and 2 approach each other so closely, there will be no room for a solvent molecule between them. Then we may question the use of the medium s r in the denominator of the related expressions, because if any polarization takes place, this may be due to a much smaller effective value of r. On the other hand, some associated solvents apply forces on solute molecules, which are determined mainly by the orientation of the molecules of 1 and 2 in the medium 3, so that the resultant distribution functions are not only functions of r but also dependent on the orientation angle. [Pg.51]

According to Frohlich, a pure condensed dielectric consisting of polarizable molecules with a permanent dipole moment p may be formally represented by a continuum permittivity accounting for the molecular polarizability, embedded in the bulk continuum with the effective permittivity 8. The fundamental polarization equation for such a polar dielectrics is... [Pg.154]

In Fig. 2, the relative permittivities (static dielectric numbers) e of carbon dioxide [23], argon [24], and liquid pentane [25] are plotted against pressure p up to 200 MPa. Even at the highest pressures corresponding to liquid-like densities, e (CO2) is smaller than 1.8, and thus nearly equal to that of a liquid alkane (such as pentane). Since CO2 molecules do not have any permanent electrical dipole moment, the polarization is more or less restricted to the contributions of the electrons and the nuclei. Therefore, typical solvation effects are normally less important, and the intermolecular interactions are predominantly of van-der-Waals type with some higher electrostatic such as quadrupolar interactions. [Pg.33]


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Dielectric effective

Dielectric effects

Dielectric permittivities

Dielectric permittivity

Dielectric polarization

Effective dielectric polarization

Effective permittivity

Molecule polarity

Molecules effects

Molecules polar molecule

Permittance

Permittivities

Permittivity

Polar effect

Polarity, effect

Polarization effects

Polarized molecules

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