Electron in liquids

For highly polar media, the yield of the solvated electron can serve as a lower limit to the ionization yield. This method needs short-time measurement and may work for liquid water and ammonia. Farhataziz et al. (1974) determined the G value—that is, the 100-eV yield—of solvated electrons in liquid NH3 to be about 3.1 at -50 ns. This corresponds to a W value of 32 eV, compared with the gas-phase value of 26.5 eV. The difference may be attributed to neutralization during the intervening time. In liquid water, it has been found that G(eh) increases at short times and has a limiting value of 4.8 (Jonah et al., 1976 Sumiyoshi et al, 1985). This corresponds to W,. = 20.8 eV compared with Wgas = 30 eV (Combecher, 1980). Considering that the yield of eh can only be a lower limit of the ionization yield, suggestions have... 

The more incisive calculation of Springett, et al., (1968) allows the trapped electron wave function to penetrate into the liquid a little, which results in a somewhat modified criterion often quoted as 47r/)y/V02< 0.047 for the stability of the trapped electron. It should be noted that this criterion is also approximate. It predicts correctly the stability of quasi-free electrons in LRGs and the stability of trapped electrons in liquid 3He, 4He, H2, and D2, but not so correctly the stability of delocalized electrons in liquid hydrocarbons (Jortner, 1970). The computed cavity radii are 1.7 nm in 4He at 3 K, 1.1 nm in H2 at 19 K, and 0.75 nm in Ne at 25 K (Davis and Brown, 1975). The calculated cavity radius in liquid He agrees well with the experimental value obtained from mobility measurements using the Stokes equation p = eMriRr], with perfect slip condition, where TJ is liquid viscosity (see Jortner, 1970). Stokes equation is based on fluid dynamics. It predicts the constancy of the product Jit rj, which apparently holds for liquid He but is not expected to be true in general. 

In most cases, the reaction requires external stimulation in which a catalytic amount of electrons is injected into the solution. Solvated electrons in liquid ammonia, sodium amalgam in the same solvent71 light,66-68 electrodes1167 and... 

Migus, A., Gauduel, Y., Martin, J. L. and Antonetti, A. Excess electrons in liquid water first evidence of a prehydrated state with femtosecond lifetime., Phys. Rev. Lett., 58 (1987), 1559-1562... 

Equilibria of this type have been used to determine the ground state of the electron in liquids [100]. Some of the values of AGs(e) given in Table 1 were evaluated this way. The reaction of the electron with COp was used to measure AGs(e) for hexamethyldisiloxane... 

Figure 4 Relative dipole oscillator strength distribution,/( ), for liquid water [63] and frequency of a given energy loss by 1-MeV electrons in liquid water [64].

It was also observed, in 1973, that the fast reduction of Cu ions by solvated electrons in liquid ammonia did not yield the metal and that, instead, molecular hydrogen was evolved [11]. These results were explained by assigning to the quasi-atomic state of the nascent metal, specific thermodynamical properties distinct from those of the bulk metal, which is stable under the same conditions. This concept implied that, as soon as formed, atoms and small clusters of a metal, even a noble metal, may exhibit much stronger reducing properties than the bulk metal, and may be spontaneously corroded by the solvent with simultaneous hydrogen evolution. It also implied that for a given metal the thermodynamics depended on the particle nuclearity (number of atoms reduced per particle), and it therefore provided a rationalized interpretation of other previous data [7,9,10]. Furthermore, experiments on the photoionization of silver atoms in solution demonstrated that their ionization potential was much lower than that of the bulk metal [12]. Moreover, it was shown that the redox potential of isolated silver atoms in water must... 

Fig. 33. Decay of the absorption at 1525 nm attributed to the solvated electron in liquid propane at 88 K irradiated with a pulse of 35 MeV electrons of duration 70 ns. The data were normalised to the initial absorption during the electron pulse and were obtained at electron doses of O, 7 X 1016 eV cm 3 n, 3.0 X 1016 eV cm 3 , 1.92 X1016 eV cm 3. After Gillis et al. [394g].

Correlation between tunneling distances for reactions of trapped electrons in vitrified solutions and the cross-sections for reactions of solvated electrons in liquid solutions... 

Of the three models that have been proposed to explain the properties of excess electrons in liquid helium, two are considered in detail (1) The electron is localized in a cavity in the liquid (2) The electron is a quasi-free particle. The pseudopotential method is helpful in studying both of these models. The most useful treatment of electron binding in polar solvents is based on a model with the solution as a continuous dielectric medium in which the additional electron induces a polarization field. This model can be used for studies with the hydrated electron. 

What information about the dynamical and statistical geometry of the liquid state can be gained by studying the behavior of excess electrons in liquids ... 

To date, three models have been proposed to explain the properties of excess electrons in liquid He ... 

The pseudopotential method is extremely useful for studying both the free and localized states of excess electrons in liquids. In the case of the free electron states, a plane wave pseudowave function can be used. This formalism is also found to be extremely useful in studying localized electron states in simple liquids (—e.g., liquid helium). A direct solution to this problem in the SCF scheme is obviously impossible at present while the pseudopotential method makes the problem tractable. 

From the gas phase scattering data we conclude that a plane wave state for the electron in liquid helium lies at positive energy relative to the vacuum level in agreement with Sommers electron injection experiment. We proceed now to a semiquantitative treatment of free electron states in liquids characterized by a positive scattering length, which will be used to estimate the energy of interaction of a free electron with liquid helium (18). 

At 4.2 °K. we find /x = 36 cm.2/volt sec. The experimental value is very different, being only 0.03 cm.2/volt sec. This discrepancy and its direction suggest that the electron is much more localized than a delocalized plane wave would allow. The analysis just described is applicable only when the electron atom pseudopotential is weak or attractive, and can therefore be used for studying low field mobility of excess electrons in liquid Ne, Ar, Kr, and Xe. 

The Bubble Model for a Localized Electron in Liquid Helium... 

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. 

What predictions for new experiments are provided by the theoretical analysis presented herein It would be extremely interesting to obtain direct spectroscopic evidence regarding the energy levels and charge distribution of the excess electron in liquid helium. Applying the pulse radiolysis technique, recently developed for studying bound electron states in polar solvents (—e.g., H20 and aliphatic alcohols), should make the localized states of an excess electron amenable to spectroscopic study. 

Absorption Spectrum of e aq. The absorption spectrum of the hydrated electron is shown in Figure 1. The evidence that this spectrum is that of eaq is at least four-fold. First, the spectrum is suppressed by known electron scavengers, such as H30+, 02, N20 (4, 18). Second, it resembles in form the absorption bands of the solvated electron in liquid ammonia and methylamine (4, 18). Third, the rate constants calculated from the decay of this absorption in the presence of scavengers... 

The energy distribution of subexcitation electrons in liquids has not been studied thoroughly, and there is only a small number of papers on the matter.143,220 In Ref. 220 the authors have found 77(E) considering the liquid as a dense gas and using the formulas for the cross sections obtained within the theory of binary collisions.146 In Ref. 143 the spectrum of subexcitation electrons was calculated using the Monte Carlo method. Apparently, it was in this study the influence the state of aggregation of water has on the energy distribution of subexcitation electrons was considered for the first time. 

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