Localized excess electron

In the case of a localized excess electron, the excess electron wave function tends toward zero for large distances from the center of localization and the liquid structure will be modified because of the following effects ... 

Simple cavity models have been used to study solvated electrons in liquid ammonia. In that case the dominant interactions arise from long range polarization effects, so that the energy of the localized state is not very sensitive to the fluid deformation in the vicinity of the localized charge. In the case of an excess electron in liquid helium, however, the electron-fluid interaction arises mainly from short range electron-atom interactions, and we shall show that the localized excess electron in a cavity in liquid helium lies lower in energy than the quasi-free electron. 

Localized Excess Electron States in Polar Solvents... 

The accumulated evidence for the electrolytic nature of dilute metal solutions is overwhelming—metal atoms introduced into a variety of nonaqueous solvents spontaneously dissociate into localized excess electrons and positive ions (37, 39, 164). 

In 1958, Pitzer (141), in a remarkable contribution that appears to have been the first theoretical consideration of this phenomenon, likened the liquid-liquid phase separation in metal-ammonia solutions to the vapor-liquid condensation that accompanies the cooling of a nonideal alkali metal vapor in the gas phase. Thus, in sodium-ammonia solutions below 231 K we would have a phase separation into an insulating vapor (corresponding to matrix-bound, localized excess electrons) and a metallic (matrix-bound) liquid metal. This suggestion of a "matrix-bound analog of the critical liquid-vapor separation in pure metals preceeded almost all of the experimental investigations (41, 77, 91,92) into dense, metallic vapors formed by an expansion of the metallic liquid up to supercritical conditions. It was also in advance of the possible fundamental connection between this type of critical phenomenon and the NM-M transition, as pointed out by Mott (125) and Krumhansl (112) in the early 1960s. 

In the period 1940-1946, Ogg (132) developed the first quantitative theory for the solvated electron states in liquid ammonia. The Ogg description relied primarily on the picture of a particle in a box. A spherical cavity of radius R is assumed around the electron, and the ammonia molecules create an effective spherical potential well with an infinitely high repulsive barrier to the electron. It is this latter feature that does not satisfactorily represent the relatively weakly bound states of the excess electron (9,103). However, the idea of a potential cavity formed the basis of subsequent theoretical treatments. Indeed, as Brodsky and Tsarevsky (9) have recently pointed out, the simple approach used by Ogg for the excess electron in ammonia forms the basis of the modem theory (157) of localized excess-electron states in the nonpolar, rare-gas systems. [The similarities between the current treatments of trapped H atoms and excess electrons in the rare-gas solids has also recently been reviewed by Edwards (59).]... 

In the following, the difference p - Pm will be designated as contrast. The local excess electron density may be spHt into a part depending on the contrast P Pm function Ap(F) independent of contrast ... 

Io(0) and the radius of gyration Rg are now related to the local excess electron density and it is easy to show that... 

By means of pulse radiolysis, two types of localized excess electrons were identified in the irradiated ice. One of them has a visible absorption band with a maximum at 630 nm (e is ) the other has an intense band in the infi ared region with rj 2,350 nm (ei, ). The two bands have different decay times and show different sensitivities to the experimental conditions. Buxton et al. (1977) suggested that the electron trap, which leads to Cyis is vacancy produced by irradiation. The other band, e r , represents an electron localized at a natural cavity in the ice. 

Localized excess electron states are energetically stable in some nonpolar solvents such as liquid He and liquid Ne. In polar solvents and in polar dense gases electron localization occurs at low concentrations. 

GENERAL FEATURES OF ELECTRON-MEDIUM INTERACTIONS Quasifree and Localized Excess Electron States... 

This condition establishes the configurational stability of the localized excess electron. The resulting energy E (R ) can be, of course, either positive or negative as the liquid rearrangement process requires the investment of energy (Ej (R )>0) which is (wholly or partially) compensated by the electronic energy... 

For alkali halide clusters it was first proposed to classify species corresponding to (i) cuboid or deformed sections of the rock salt lattice with the localized excess electrons in the vacancy (surface F-centers), for which relatively high IPs were measured and a strong absorption in the visible-infrared region, in analogy with the bulk color centers, is expected (ii) filled cuboids with excess electrons highly delocalized... 

At the beginning of the century, nobody knew that a small proportion of atoms in a crystal are routinely missing, even less that this was not a mailer of accident but of thermodynamic equilibrium. The recognition in the 1920s that such vacancies had to exist in equilibrium was due to a school of statistical thermodynamicians such as the Russian Frenkel and the Germans Jost, Wagner and Schollky. That, moreover, as we know now, is only one kind of point defect an atom removed for whatever reason from its lattice site can be inserted into a small gap in the crystal structure, and then it becomes an interstitial . Moreover, in insulating crystals a point defect is apt to be associated with a local excess or deficiency of electrons. 

Fig. 8. Scheme of the electronic structure of (A) [3Fe-4S] centers and (B) [4Fe-centers according to the standard model. The thin and thick dashed fines indicate the Emtiferromagnetic and double exchEmge coupling, respectively. Configurations a and b correspond to the two possible locations of the excess electron in the mixed-valence pair. In part (B), the local spin values are Sc = Sd = 2 in the case of [4Fe-4S] centers and Sc = Sd = i in the case of [4Fe-4S] + centers. 

C and C are the electrostatic attractive interactions of the excess electron of one fragment with the electron hole of the other fragment and G and G are local fragment excitation energies. 

The charge on the surface of an ionic conductor arises from a local excess of cations over anions or anions over cations. For example if the surface of Na-) -Al203 has a positive charge there will be an excess of Na ions in the surface of the electrolyte over the number of Na" ions which would be required to maintain electroneutrality. Likewise if the surface has a negative charge there will be an overall deficit of Na" ions compared with the number required for electroneutrality. For a metal surface the surface charge (an excess or deficit of electrons) is generally assumed to be within 10 pm of the surface. 

Fe—2S] clusters cysteines, 38 294 P-band spectrum, 38 191-192 X-band spectrum, 38 189 [2Fe—2S] clusters EPR spectroscopy, 38 187 excess electron localization, 38 179-180 [3Fe-4S] clusters, 38 16-24, 119-120 conversion reactions, 38 17-18 D. africanus Fd III, 38 138-144 electronic structure, 38 19 electron transfer series, 38 18-19 formation, oxidation and spin states, 38 17-22... 

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