Interaction with an electric field

The dielectric constant of a polymer (K) (which we also refer to as relative electric permittivity or electric inductive capacity) is a measure of its interaction with an electrical field in which it is placed. It is inversely related to volume resistivity. The dielectric constant depends strongly on the polarizability of molecules tvithin the polymer. In polymers with negligible dipole moments, the dielectric constant is low and it is essentially independent of temperature and the frequency of an alternating electric field. Polymers with polar constituents have higher dielectric constants. When we place such polymers in an electrical field, their dipoles attempt... 

Until quite recently, however, theoretical prediction of NMR spectral properties significantly lagged experimental work. The ultimate factor slowing theoretical work has been simply that it is more difficult to model the interactions of a wave function with a magnetic field than it is to model interactions with an electric field. Nevertheless, great progress has been made over the last decade, particularly with respect to DFT, and calculation of chemical shifts is becoming much more routine than had previously been true. 

There are several ways of expressing ionic mobility. According to one of them, the absolute mobility, is the velocity of an ion under an applied force of 1 dyne. The conventional mobility, on the other hand, is the velocity under the force exerted on an ion by its interaction with an electric field of 1 V cm . Deduce the relation between and... 

An enzyme or transporter must be able to interact with an electric field. This simply means that there is charge displacement in its structure that is associated with the T to T2 transition. An electric field favors a state with greater electric moment (assuming T2) than a state with smaller electric moment (assuming Tx). If the Tx to T2 transition changes the molar electric moment of the transporter by AMe, an electric field of Em will effect a shift in the equilibrium according to eq 6. 

In much the same way it can be proven that the total energy of a molecule interacting with an electric field with uniform field gradient is origin independent [56]. 

Consider an ensemble of non-degenerate two-level quantum systems interacting with an electric field, E (j[l,t) through the electric dipole interaction. In the absence of collisions, the quantum mechanical Hamiltonian for the j th molecule isl 7... 

For a molecule with a permanent electric dipole moment y the Hamiltonian for interaction with an electric field is ... 

The orientation process in a LC polymer is a result of its dielectric interaction with an electric field. The duration of this process depends on the polymerization degree, the greater the polymerization degree, the lon-... 

The dielectric constant, which determines how the dielectric material interacts with an electric field, is a characteristic property of dielectrics. It is a measure of the charge retention capacity of a medium. In general, low dielectric constants result in faster substrates, whereas large dielectric constants... 

If the electron is assumed to have an electric dipole moment of dg, then the interaction with an electric field E is given as... 

As our discussion of scattering proceeds, we shall examine the coupling between the oscillating electrical field of light and the electrons of the scatterer in detail. First, it is useful to consider the interaction of an electric field with matter, as this manifests itself in the dielectric behavior of a substance. This will not only introduce us to the field-matter interaction, but will also provide some relationships which will be useful later. 

The dielectric materials interact with the electrical fields and alter the characteristics of the electrical field. In some cases this is desirable and in others it is deleterious to the operation of the system and must be minimized. This is done by both the selection of the material and the configuration of the dielectric. To see how these concepts are applied, an example is presented of one of the major applications of plastics materials, i.e., to insulate wires, and show how a dielectric is designed to meet the service requirements. The specific requirements on a standard wire are ... 

Polyelectrolytes such as the ion exchange plastics form an interesting group of materials because of their ability to interact with water solutions. They have been used in medical applications involving the removal of heavy metal ions from the human body. They can be used to interact with external electric fields and change their physical properties drastically as is illustrated by the fact that some electrically active liquid crystals are polyelectrolytes of low molecular weight. 

Many of the initial theoretical models used to vahdate the concept of coherent control and optimal control have been based on the interaction of the electric field of the laser light with a molecular dipole moment [43, 60, 105]. This represents just the first, or lowest, term in the expression for the interaction of an electric field with a molecule. Many of the successful optimal control experiments have used electric fields that are capable of ionizing the molecules and involve the use of electric field strengths that lead to major distortions of the molecular electronic structure. With this in mind, there has been discussion in the... 

We can divide commodity plastics into two classes excellent and moderate insulators. Polymers that have negligible polar character, typically those containing only carbon-carbon and carbon-hydrogen bonds, fall into the first class. This group includes polyethylene, polypropylene, and polystyrene. Polymers made from polar monomers are typically modest insulators, due to the interaction of their dipoles with electrical fields. We can further divide moderate insulators into those that have dipoles that involve backbone atoms, such as polyvinyl chloride and polyamides, and those with polar bonds remote from the backbone, such as poly(methyl methacrylate) and poly(vinyl acetate). Dipoles involving backbone atoms are less susceptible to alignment with an electrical field than those remote from the backbone. 

Any periodic distortion that causes polarization of a molecule can also cause interaction with the electric field component of radiation. An example is the asymmetric stretching vibration of the CO2 molecule, that creates a fluctuating dipole moment as shown below. 

T IE- E j erj IT/2 >. Here E Ej eri is the one-electron operator describing the interaction of an electric field of magnitude and polarization E with the instantaneous dipole moment... 

The modification of the electronic potentials due to the interaction with the electric field of the laser pulse has another important aspect pertaining to molecules as the nuclear motion can be significantly altered in light-induced potentials. Experimental examples for modifying the course of reactions of neutral molecules after an initial excitation via altering the potential surfaces can be found in Refs 56, 57, where the amount of initial excitation on the molecular potential can be set via Rabi-type oscillations [58]. Nonresonant interaction with an excited vibrational wavepacket can in addition change the population of the vibrational states [59]. Note that this nonresonant Stark control acts on the timescale of the intensity envelope of an ultrashort laser pulse [60]. 

In this section we discuss the interaction between an electric field and a charge that is free to move with the field. Such a charge experiences a force that accelerates it with the field. If the field is oscillating, the acceleration of the charge will also oscillate. One of the basic results of classical electromagnetics is that the acceleration of a charge leads to the emission of radiation. 

FIG. 5.4 Coordinates and acceleration relevant to the interaction of an electric field with a charge (a) the coordinates of an electric field E relative to an oscillating charge located at the origin (b) projection of the acceleration in the plane perpendicular to the line of sight. 

Once ionized, the analyte ions are separated by their interaction with an electric or magnetic field in a high vacuum (usually —10 " —10 N m , which is 10 —10 bar) in order to minimize the interaction of the gaseous analyte ions with molecules in the air. In some cases, the mass analysis process can be made to produce data with high mass accuracy. The various options for the process of mass analysis are discussed in Section 5.4. 

All of the heteroatoms possess at least one naturally occurring isotope with a magnetic moment (Table 15). The nuclei 14N, 170 and 33S also possess an electric quadrupole moment which interacts with the electric field gradient at the nucleus, providing a very efficient mechanism for relaxing the nuclear spin. The consequence of this facilitation of relaxation is a broadening of the NMR signals so that line widths may be 50-1000 Hz or even wider. To some extent this problem is offset by the more extensive chemical shifts that are observed. The low natural abundances and/or sensitivities have necessitated the use of accumulation techniques for all of these heteroatoms. The relative availability of 170 and 15N enriched... 

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