Electric symmetry

The electricity-producing system of electric fishes is built as follows. A large number of flat cells (about 0.1 mm thick) are stacked like the flat unit cells connected in series in a battery. Each cell has two membranes facing each other. The membrane potentials of the two membranes compensate for each other. In a state of rest, no electrostatic potential difference can be noticed between the two sides of any cell or, consequently, between the ends of the stack. The ends of nerve cells come up to one of the membranes of each cell. When a nervous impulse is applied from outside, this membrane is excited, its membrane potential changes, and its permeability for ions also changes. Thus, the electrical symmetry of the cell is perturbed and a potential difference of about 0.1 V develops between the two sides. Since nervous impulses are applied simultaneously to one of the membranes in each cell, these small potential differences add up, and an appreciable voltage arises between the ends of the stack. 

The intensity of an infrared absorption band arising from changes in the vibrational energy is related to the electrical symmetry of the bond. More symmetrical, less polarized bonds give weaker absorptions. In fact, if the bond is completely symmetrical, there is no infrared absorption. In contrast, unsym-metrical molecules in which the bonds are quite polarized, such as C=0 bonds, show strong infrared absorptions. 

Larter, R. Ortoleva, P. J. Theoret. Biol., "A Study of Instability to Electrical Symmetry Breaking in Unicellular Systems" (submitted for publication). 

An infrared spectrum thus represents the attenuation of the incident radiation as a function of frequency each absorption band corresponding to a jump between two vibrational levels and a specific vibrational movement. Moreover, the activity (a mode is said to be active when the corresponding absorption band can be detected) of the vibrational mode depends on the variation in an electrical property of the molecule, namely its dipole moment. In the case of a homonuclear molecule, such as N2 for example, the electrical symmetry is maintained during the elongation movement along the axis which connects the two nitrogen atoms and the corresponding absorption transition is prohibited. 

Let us consider the influence of metal d electrons on structure. If there are zero, five (unpaired), or ten d electrons present in the outer d subshell of an atom, there is no distortion of the structure of its complexes. This is true because empty, half-filled, and filled d subshells have spherical electrical symmetry a charged particle (for example, a ligand) on a sphere having the metal at its center will encounter the same electrostatic force regardless of its position on the sphere. Therefore, the position that a ligand will occupy is not influenced by d electrons in these cases. 

The birefringence of a spherulite A s is defined as — n, where is the refraetive index parallel to the spherulite radius and n, is the refractive index perpendicular (tangential) to the radial direction. If the amorphous phase is assumed to be isotropic. A j is directly related to the orientation of crystallites with respect to the radial direction in the spheruhte In polymer crystals, the largest refractive index 3 is along the molecular chain axis, while j and 2 are the refractive indices along the electric. symmetry axes perpendicular to the chain axis. 

The R oscillation can thus be seen as a mechanism able to generate a net electronic charge transfer along the doped chain within the doped domain. This mechanism is made possible by the breakdown of the electrical symmetry of carbon-carbon bonds induced by doping or photoexcitation. It must be remembered that the R oscillation is IR-inactive by symmetry (Ag mode) in the neutral species. 

It has already been pointed out that a modulation of the structure is related to a modulation of the intensity pattern. Starting from a centrosymmetric polyene structure (alternated), it is known that modes have selectively enhanced Raman intensities and vanishing infrared activities. As soon as electrical symmetry is broken, a variation of the dimerization is induced, thus determining an enhancement of the Raman intensity and the simultaneous activation of the modes in the infrared spectrum. This means that the molecule becomes /3-active and its NLO response increases as the degree of alternation decreases. Thus 3 reaches a maximum value after which the Raman intensity starts decreasing... 

A dipole may be created or induced in an atom or molecnle that is normally electrically symmetric—that is, the overall spatial distribution of fhe electrons is symmetric with respect to the positively charged nnclens, as shown in Fignre 2.21a. All atoms experience constant vibrational motion that can canse instantaneons and short-lived distortions of this electrical symmetry for some of the atoms or molecnles and the creation of small electric dipoles. One of these dipoles can in turn produce a displaeement of the electron distribntion of an adjacent molecnle or atom, which induces the second one also to become a dipole that is then weakly attracted or bonded to the first (Figure 2.21fe) this is one type of van der Waals bonding. These attractive forces, which forces are temporary and fluctuate with time, may exist between large numbers of atoms or molecules. 

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