Dipole Alignment of Ions

The other mechanism of ion ahgnment is the orientation of ion dipole that, in general, comprises permanent and induced components.Their effects are considered in 2.7.1 through 2.7.3 and 2.7.4, respectively. 

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Coulomb field of an ion packet Minimum and maximum E allowing dipole alignment of ions Normalized field intensity... 

Shvartsburg, A.A., Bryskiewicz, T., Purves, R.W., Tang, K., Guevremont, R., Smith, R.D., Field asymmetric waveform ion mobility spectrometry studies of proteins dipole alignment in ion mobility spectrometry J. Phys. Chem. B 2006, 110, 21966. 

While the FAIMS separation power for macroions may be greatly raised by reversible alignment of ion dipoles in asymmetric electric field (3.3.5), the extraction of absolute collision cross sections and thus ion geometries from such data has... 

Only at extremely high electric fields are the water molecules fiilly aligned at the electrode surface. For electric fields of the size normally encountered, a distribution of dipole directions is found, whose half-widtli is strongly dependent on whether specific adsorption of ions takes place. In tlie absence of such adsorption the distribution fiinction steadily narrows, but in the presence of adsorption the distribution may show little change from that found at the PZC an example is shown in figure A2.4.10 [30]. 

If we had any means of reducing the electrostatic repulsion without, at the same time, affecting the quantum-mechanical attraction, we should have the possibility of forming such doubly charged molecular ions. Now a polar solvent has just the required properties the alignment of the solvent dipoles greatly reduces the electrostatic repulsion, but the quantum-mechanical forces of attraction arise from the rapid motion of... 

Note that two distinct types of interactions (ion-quadrupole and dipole-dipole) contribute to an overall R 3 dependence, and the number of distinct multipole types having similar R n dependences continues to increase with increasing n. For uncharged systems, the dipole-dipole interaction (5.23d) is expected to dominate, with an angular term that favors parallel alignment of the two dipoles. 

In the gas phase the dipole moment determined through Eq. (4.10) refers to an individual adsorbed particle. This is not so in the electrochemical situation. The dipole moment of an adsorbed species will tend to align neighboring solvent molecules in the opposite direction, thereby reducing the total dipole potential drop (see Fig. 4.3). Only the total change in dipole potential can be measured, and there is no way of dividing this into separate contributions from the adsorbate bond and the reorientation of the solvent. The apparent dipole potential of an ion adsorbed from a solution on a particular metal is often substantially smaller than that of the same ion adsorbed in the vacuum (see Table 4.1), since it contains a contribution from the solvent. For comparison we note that the dipole moments of alkali ions adsorbed from the vacuum are usually of the order of the order of 10 29 C m. 

An interesting observation should be made concerning the dependence of the physical properties on molecular cyclicity, since it will have a significant effect on the formulation of electrolytes for lithium ion cells. While all of the ethers, cyclic or acyclic, demonstrate similar moderate dielectric constants (2—7) and low viscosities (0.3—0.6 cP), cyclic and acyclic esters behave like two entirely different kinds of compounds in terms of dielectric constant and viscosity that is, all cyclic esters are uniformly polar (c = 40—90) and rather viscous rj = 1.7—2.0 cP), and all acyclic esters are weakly polar ( = 3—6) and fluid (77 = 0.4—0.7 cP). The origin for the effect of molecular cyclicity on the dielectric constant has been attributed to the intramolecular strain of the cyclic structures that favors the conformation of better alignment of molecular dipoles, while the more flexible and open structure of linear carbonates results in the mutual cancellation of these dipoles. 

In some ceramic compounds, the different kinds of ions possess different and strong magnetic dipoles. In addition, both kinds are partially oppositely aligned in an external field. Since the sizes of the magnetization are unequal, the result is a net magnetization which can considerably reinforce the external field. This is called ferrimagnetism. 

Figure 3. Different mechanisms for inducing polarization through (a) redistribution of electron density, (b) bond stretching, (c) alignment of dipoles, and (d) separation of ions.

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