Solvated electron shell

The general or universal effects in intermolecular interactions are determined by the electronic polarizability of solvent (refraction index n0) and the molecular polarity (which results from the reorientation of solvent dipoles in solution) described by dielectric constant z. These parameters describe collective effects in solvate s shell. In contrast, specific interactions are produced by one or few neighboring molecules, and are determined by the specific chemical properties of both the solute and the solvent. Specific effects can be due to hydrogen bonding, preferential solvation, acid-base chemistry, or charge transfer interactions. 

Background alkali metal chemistry. The alkali metals have the lowest ionization potentials of any group in the periodic table and hence their chemistry is dominated by the M+ oxidation state. However, it has been known for some time that a solution of an alkali metal (except lithium) in an amine or ether forms not only M+ ions and solvated electrons but also alkali anions of type M (Matalon, Golden Ottolenghi, 1969 Lok, Tehan Dye, 1972). That is, although an alkali metal atom very readily loses its single s-shell electron ... 

As already stated, the diffusion coefficient and mobility of a solvated electron, though much smaller than that of a free electron in a conduction band, are some 4-5 times larger than for the solvated cation. There is some doubt whether the electron carries along a solvated shell with it, and there has been discussion in the literature of mechanisms by which molecules drift across the cavity, changing their orientation as they do so. 

In aqueous solutions, it has been shown that the solvated electron e" circulates in the solvation shell until it is captured by I2 to given an I, radical ion which is finally stabilized to I . The solvated electrons have a characteristic absorption band near 700 nm which has been detected in flash pbotolytic studies of aqueous KI. The orbital of the excited electron may be considered to be spherically symmetric like that of a hydrogen atom, with its centre coinciding with the centre of the cavity containing the ion. 

Some solvated anions like I-, Fe (CN)j - r phenate, etc. eject an electron into the solvation shell on electronic excitation. Such a solvated electron thus generated, absorbs at 700 nm as observed by flash photolysis. 

When an electron is injected into a polar solvent such as water or alcohols, the electron is solvated and forms so-called the solvated electron. This solvated electron is considered the most basic anionic species in solutions and it has been extensively studied by variety of experimental and theoretical methods. Especially, the solvated electron in water (the hydrated electron) has been attracting much interest in wide fields because of its fundamental importance. It is well-known that the solvated electron in water exhibits a very broad absorption band peaked around 720 nm. This broad absorption is mainly attributed to the s- p transition of the electron in a solvent cavity. Recently, we measured picosecond time-resolved Raman scattering from water under the resonance condition with the s- p transition of the solvated electron, and found that strong transient Raman bands appeared in accordance with the generation of the solvated electron [1]. It was concluded that the observed transient Raman scattering was due to the water molecules that directly interact with the electron in the first solvation shell. Similar results were also obtained by a nanosecond Raman study [2]. This finding implies that we are now able to study the solvated electron by using vibrational spectroscopy. In this paper, we describe new information about the ultrafast dynamics of the solvated electron in water, which are obtained by time-resolved resonance Raman spectroscopy. 

The separation distance R should affect primarily the orientation polarization contribution to X rather than the vibrational contribution from the inner coordination shell (5). If R is about the same for this reaction as it is for reaction with the solvated electron then X2 is the same. The difference in X2 would probably be relatively minor in any case for typical R9 s. 

We come here to a rather special concept of condensed-phase e.t. reactions, according to which the solvent itself would act as an intermediary between the actual electron acceptor and electron donor partners. According to this model, each molecule would be surrounded by a solvent cage which would keep them seperated, so that the solvated electron would be the primary species formed by e.t., from the donor, as well as the actual donor to the final electron acceptor. In Fig. 10 this model is illustrated for the case of two spherical molecules embedded in their specific solvation shells, although the word specific is not clearly defined in this respect. 

Solvated electrons are commonly thought to have a solvation shell somewhat similar to that of a normal anion such as Cl-. Solvation occurs in less than 1 ps and the resulting e-aq units are much less reactive than dry electrons). Relatively low yields of hydrogen atoms are also present, possibly formed from H20 homolysis, or from reaction between dry electrons and H20 (to give H and OH-), and also H202 seems to be formed at a very early stage. However, the main reactive radicals are OH and e-aq. 

Narayana M, Kevan L. (1980) Electron spin echo modulation study of the geometry of solvated electrons in ethanol glass An example of a molecular dipole oriented solvation shell. J Chem Phys 72 2891-2892. 

The solvated electron in ammonia has a strong absorption band in the infrared region, and /Imax shifts from 1850 nm at 23 °C to 1410 nm at —75°C this is attributed to the effect of temperatiu-e on the orientation of the ammonia molecules in the first solvation shell [37], On the other hand, G(e am) = 0-32 pmol J remains constant over the same temperature range [37]. It is relatively straightforward, therefore, to study one-electron redox reactions in liquid ammonia by pulse radiolysis, but relatively few investigations have been made. 

Of interest are the results obtained in studies not of the excess electrons themselves, but of solvent (e.g. hexamethylphosphotriamide) molecules on introducing the solvated electrons. In the Raman spectrum, obtained by the coherent ellipsometry method, with the introduction of solvated electrons a positive shift in the C—H bond vibrational frequency is observed This has been attributed to the appearance of increased electron density at the C—H bond when a hexamethylphosphotriamide molecule enters into the solvate shell of an electron. 

In Section 2 we estimated the reorganization energy for an isolated solvated electron (in fact, we talked therein about the reorganization energy for the process of removing an electron from its solvation shell to infinity). In the case of the... 

Many of the available computations on radicals are strictly applicable only to the gas phase they do not account for any medium effects on the molecules being studied. However, in many cases, medium effects cannot be ignored. The solvated electron, for instance, is all medium effect. The principal frameworks for incorporating the molecular environment into quantum chemistry either place the molecule of interest within a small cluster of substrate molecules and compute the entire cluster quantum mechanically, or describe the central molecule quantum mechanically but add to the Hamiltonian a potential that provides a semiclassical description of the effects of the environment. The 1975 study by Newton (28) of the hydrated and ammoniated electron is the classic example of merging these two frameworks Hartree-Fock wavefunctions were used to describe the solvated electron together with all the electrons of the first solvent shell, while more distant solvent molecules were represented by a dielectric continuum. The intervening quarter century has seen considerable refinement in both quantum chemical techniques and dielectric continuum methods relative to Newton s seminal work, but many of his basic conclusions... 

Solvated electrons appear to be characteristic of small anions with regard to their equilibrium solvation shell structures. For example, the OH bond orientation of water around solvated electrons can be compared with the same water orientation around fluoride ion in hydrated crystals of KF [Be 64]. Electron spin echo modulation studies have been suggested [Ic 80] therefore for the study of the solvation shell structure of anions. Tetracyanoethylene anion (TCNE ) was found to be a suitable model. The investigations were performed in the frozen solutions with CD3OH, CH3—OD, CD3CO and ( 03)280 at 4.2 K temperature. The results indicated that TCNE" is solvated by four methanol molecules with the methanol molecular dipole oriented toward the anion the distances from the anion to the hydroxyl and methyl deuterons are 0.59 and 0.38 nm, respectively. TCNE" is solvated by two molecules of acetone or dimethyl sulphoxide it is suggested that these solvating molecules are above and below the TCNE" plane with their molecular dipoles oriented toward the C=C bond in TCNE". 

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