Electron liquid water

The fimctiong(ri is central to the modem theory of liquids, since it can be measured experimentally using neutron or x-ray diffraction and can be related to the interparticle potential energy. Experimental data [1] for two liquids, water and argon (iso-electronic with water) are shown in figure A2.4.1 plotted as a fiinction ofR = R /a, where a is the effective diameter of the species, and is roughly the position of the first maximum in g (R). For water, a = 2.82 A,... 

One of the most efficient ways to treat this problem is to combine the ab initio MO method and the RISM theory, and this has been achieved by a slight modification of the original RISM-SCF method. Effective atomic charges in liquid water are determined such that the electronic structure and the liquid properties become self-consistent, and along the route of convergence the polarization effect can be naturally incorporated. 

Mahoney MW, Jorgensen WL (2001) Rapid estimation of electronic degrees of freedom in Monte Carlo calculations for polarizable models of liquid water. J Chem Phys 114(21) 9337-9349... 

Curioni et al.148 studied the protonation of 1,3-dioxane and 1,3,5-trioxane by means of CP molecular dynamics similations. The dynamics of both molecules was continued for few ps following protonation. The simulation provided a detailed picture the evolution of both the geometry and the electronic structure, which helped to rationalize some experimental observations. CP molecular dynamics simulations were applied by Tuckerman et al.149,150 to study the dynamics of hydronium (H30+) and hydroxyl (OH-) ions in liquid water. These ions are involved in charge transfer processes in liquid water H20 H+. .. OH2 - H20. .. H+-OH2, and HOH. . . OH- -> HO-. . . HOH. For the solvatetd H30+ ion, a picture consistent with experiment emerged from the simulation. The simulation showed that the HsO+ ion forms a complex with water molecules, the structure of which oscillates between the ones of H502 and I L/ij clusters as a result of frequent proton transfers. During a consid-... 

Table 2.1 summarizes some of the events that occur in radiation chemistry through the various stages. The earliest discernible time, obtained from uncertainty principle, AE At - fi, is 1CH7 s, which accounts for the production of fast secondary electrons with energy > 100 eV Times shorter than these are just computed values. It has been suggested that, following ionization in liquid water, the dry hole H20+ can move by exact resonance until the ion-molecule reaction H20+ + H20 — H30+ + OH localizes the hole. The... 

Finally, the integral of the oscillator strength up to E = 30 eV only amounts to -3.0 in both gaseous and liquid water, which falls much shorter than the value 10 if all the electrons were to participate in plasma excitation, giving an excitation energy -21 eV... 

FIGURE 3.5 Energy partition among the track entities (spurs, blobs, and short tracks) as a function of electron energy in liquid water. Data from Pimblott et at. (1990), with permission of Am. Chem. Soc. ... 

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... 

Integral W values oj ionization for incident electron energies E, as measured in Combecher s (1980) experiments on gaseous water, can be well fitted by the equation W(E) = W(°°)(l - I/E)-1, where W(°°) = 30.0 eV is the value in the high-energy limit. A similar equation is assumed for liquid water. In contrast, the entity-specific Wi value of ionization, defined for a certain energy deposition in a spur, shows a minimum at 20 eV in... 

When averaged over the distribution of energy loss for a low-LET radiation (e.g., a 1-MeV electron), the most probable event in liquid water radiolysis generates one ionization, two ionizations, or one ionization and excitation, whereas in water vapor it would generate either one ionization or an excitation. In liquid water, the most probable outcomes for most probable spur energy (22 eV) are one ionization and either zero (6%) or one excitation (94%) for the mean energy loss (38 eV), the most probable outcomes are two ionizations and one excitation (78%), or one ionization and three excitations (19%). Thus, it is clear that a typical spur in water radiolysis contains only a few ionizations and/or excitations. 

The first subnanosecond experiments on the eh yield were performed at Toronto (Hunt et al., 1973 Wolff et al., 1973). These were followed by the subnanosecond work of Jonah et al. (1976) and the subpicosecond works of Migus et al. (1987) and of Lu et al. (1989). Summarizing, we may note the following (1) the initial (-100 ps) yield of the hydrated electron is 4.6 0.2, which, together with the yield of 0.8 for dry neutralization, gives the total ionization yield in liquid water as 5.4 (2) there is -17% decay of the eh yield at 3 ns, of which about half occurs at 700 ps and (3) there is a relatively fast decay of the yield between 1 and 10 ns. Of these, items (1) and (3) are consistent with the Schwarz form of the diffusion model, but item (2) is not. In the time scale of 0.1-10 ns, the experimental yield is consistently greater than the calculated value. The subpicosecond experiments corroborated this finding and determined the evolution of the absorption spectrum of the trapped electron as well. 

Mozumder s (1988) conjecture on electron thermalization, trapping and solvation time scales in liquid water is based on combining the following theoretical and experimental information ... 

Tapia, O., Colonna, F. and Angyan, J. G. Generalized self-consistent reaction field theory in multicenter-multipole ab initio LCGO framework. I. Electronic properties of the water molecule in a Monte Carlo sample of liquid water molecules studied with standard basis sets, J.ChimPhys., (1990), 875-903... 

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... 

Pommeret, S., Antonetti, A. and Gauduel, Y. Electron hydration in pure liquid water. Existence of two nonequilibrium configuration in the near-IR region, JAm.Chem.Soc., 113 (1991). 9105-9111... 

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