Electric field orientation

A paraelectric substance is not polarized macroscopically because the dipoles are oriented randomly. However, they can be oriented by an external electric field (orientation polarization). The orientation is counteracted by thermal motion, i.e. the degree of polarization decreases with increasing temperature. 

The general problem of the orienting effect of a static electric field (orientation of polar molecules) was first considered by Debye [6, 7], Frolich [8], and more recently Bottcher [9,10]. 

In contrast, the n ==> Jt transition has a ground-excited state direct product of B2 x Bj = A2 symmetry. The C2V s point group character table clearly shows that the electric dipole operator (i.e., its x, y, and z components in the molecule-fixed frame) has no component of A2 symmetry thus, light of no electric field orientation can induce this n ==> Jt transition. We thus say that the n ==> 7t transition is El forbidden (although it is Ml allowed). 

Effects of Electric Field Orientation of Molecules in a Magnetic Field... 

Measurement of practical standard value of parallelism degree in the orientation of polymer main chains in an electric-field-oriented film. 

Molecular Design for Enhanced Electric Field Orientation of Second-Order Nonlinear Optical... 

When a photon reflects off any molecule, the orientation of the electric field produced by that photon is rotated. The mirror image of that molecule will rotate the electric field to the same degree but in the opposite direction. In a typical compound where a photon is just as likely to collide with either mirror image, there are so many millions of molecules producing so many collisions that the photon is most likely to leave the compound with the same electric field orientation with which it... 

When an electric field is applied to an ideal dielectric material there is no long-range transport of charge but only a limited rearrangement such that the dielectric acquires a dipole moment and is said to be polarized. Atomic polarization, which occurs in all materials, is a small displacement of the electrons in an atom relative to the nucleus in ionic materials there is, in addition, ionic polarization involving the relative displacement of cation and anion sublattices. Dipolar materials, such as water, can become polarized because the applied electric field orients the molecules. Finally, space charge polarization involves a limited transport of charge carriers until they are stopped... 

Fig. 10. Dependence of the steady-state dipolar splitting upon the polymer concentration. 1, PELG in CH2CI2 (+, equal proportions of PELG and PEDG) 2, PELG in CH2Br2. The full lines are for the magnetic-field orientation and the broken lines for the electric-field orientation. The d ree of polymerization of the polypeptides is approximately 1500...

No change in the splitting is observed when tire NMR sample tube is rotated by 180° after the steady-state separation is reached, indicating that the magnetic-field orientation is caused by the induced (magnetic) dipoles of the polymer molecules in contrast to the electric-field orientation in high dielectric solvent... 

The 90 geometry of Figure 6.25 does not require a polarizer to determine p but does require rotation of the laser polarization. The intensity (/j) is determined with the laser electric field oriented on the y axis, with the observation axis along the x axis. Then the laser electric field is rotated 90 (usually with a quarter wave plate) to position it parallel to the x axis. The observed intensity is now /x, and p may be calculated directly from the two spectra. 

In the linear-response range, a time-dependent electric field oriented along the axis ... 

Figure 2-4. A simplified scheme of the proposed water-gated mechanism of proton translocation. Each numbered state shows haem a and the binuclear site (left and right rectangles, respectively) the A-propionate of haem is shown schematically. Three water molecules (oxygen in red hydrogen in yellow) are shown to mediate Grotthuss proton transfer from the glutamic acid (GLU-OH) to the propionate or the binuclear site, respectively. In state 1, an electron is transferred to haem a. The formed electric field between the redox sites orientates the water molecules towards the propionate (state 2). In state 3, electron transfer to the binuclear site is accompanied by proton transfer via the propionate a proton is deposited above haem and the glutamate is reprotonated via the D-pathway (state 4). The switch of electric field orientation reorientates the water array towards the binuclear site (state 5). Finally, a proton is transferred to this site, and the first proton is ejected (state 6). Reprotonation of the glutamate transfers the system back to state 1. For details, see the text and ref. 17.

Yamaoka K, Fukudome K. Electric field orientation of nucleic acids in aqueous solutions. 1. Dependence of steady-state electric birefringence of rodlike DNA on field strength and the comparison with new theoretical orientation functions. J Phys Chem 1988 92 4994-5001. 

When such a permanent dipole is placed in an electric field, orientation takes place as the molecule attempts to align with the field in order to adopt a low-energy configuration. This orientation is clearly time dependent and gives rise to Pd(t), the time-dependent macroscopic polarization discussed previously. 

From this and what has been mentioned so far, the electric-field orientation of liquid crystalline solutions of polypeptides in high dielectric solvent must be caused by the excess of the dipole moments due to fluctuation of the distribution in the molecular cluster. The number of polymer molecules in the cluster, N, may be given in the form /N = 730 for PBLG (of degree of polymerization 650) in methylene bromide (see Section III-B), and the following result is obtained ... 

---