Électrons en excès dans les milieux polaires homogènes et hétérogènes

Abstract

RCsumC : Une synthkse des connaissances actuelles concernant la solvatation des Clectrons en excks (e,,, + e-s,l,) produits par photoionisation ou par radiolyse dans les milieux polaires a Ct C tentee. Sont successivement envisagees les diverses propriCtCs de l'espece alors forrnCe : les rnCcanisrnes proposCs pour sa solvatation, sa structure, ses caractCristiques physico-chimiques. En dCpit de certaines analogies entre les anions halogenure solvatCs et e-,,,, celui-ci ne parait pas pouvoir en constituer le prototype. Le cornporternent de e; , , dans des systkmes hCtCrogknes modeles, tels que solutions micellaires et agrCgats molCculaires, est tgalement abordC et corrC1C aux rCsultats relatifs aux solutions homogenes.Mots c l b : electrons en excks, milieux polaires homogknes et hCtCrogenes, photoionisation, radiolyse, solvatation, transfert de charge au solvant, propriCtCs de I'Clectron solvatC, solutions micellaires, agrCgats moleculaires, comparaison avec la solvatation des anions.Abstract: A review of our present knowledge concerning the solvation of excess electrons (e-,,, + e-,,lv) produced by photoionization or radiolysis in polar media has been attempted. Various properties of the solvated electron (proposed solvation mechanisms, structure, physicochemical characteristics) are considered. In spite of some similarities, e-,,,, does not seem to be a good prototype for solvated halide anions. The behavior of e-,,, in heterogeneous model systems, such as micellar solutions and molecular clusters, is described and correlated with that observed in homogeneous media.

Effect of water density on the absorption maximum of hydrated electrons in sub- and supercritical water up to 400 °C

“…4, the temperature corresponding to = 0.65 g / cm 3 at 25 MPa is ϳ358°C. 17,34,43,44 Simple microscopic arguments, based on the large density fluctuations ͑or inhomogeneities͒ and the highly disrupted hydrogen-bond network associated with criticality, can be employed to attempt to shed some light on the molecular-level mechanisms underlying the localization and hydration of excess electrons in near-critical water and SCW. In contrast, at higher temperatures and especially above t c , the two curves move away from each other owing to the fact that the density of water at 25 MPa decreases quickly with increasing temperature.…”

“…As a result, the instantaneous picture of SCW can be viewed as that of an inhomogeneous medium with coexisting high-and low-density regions. 16,17 In fact, secondary ͑or "dry"͒ electrons slow down to subexcitation energies and, following thermalization, get localized ͑or "trapped," then forming the so-called "wet" electrons whose exact physical nature is still the subject of investigation͒ and eventually become hydrated ͑for example, see Refs. 11 With increasing temperature and/or decreasing density, the hydrogen bonding becomes weaker and less persistent, and correspondingly the average cluster size ͑characterized by the number of water molecules belonging to it, n͒ decreases.…”

“…11 With increasing temperature and/or decreasing density, the hydrogen bonding becomes weaker and less persistent, and correspondingly the average cluster size ͑characterized by the number of water molecules belonging to it, n͒ decreases. 17,[23][24][25][26][27][28][29][30][31][32][33] Moreover, a series of pulse radiolysis experiments has shown that hydrated electrons can form in irradiated water up to the critical temperature and beyond. 12,13 For example, at the supercritical conditions of ϳ400-800°C and ϳ0.12-0.66 g / cm 3 , these simulations indicate that although most water molecules exist as single entities or small clusters ͑n = 5 or less͒, larger molecular clusters ͑n Ն 20͒ might also exist.…”

Electron affinity of liquid water

“…Figure 2 shows the electron energy diagram in liquid water constructed from our EA calculations and the most recent measurements for AEA, VDE, and μ . Specifically, AEA = 1.34 eV was obtained by extrapolation of water cluster data 46 ; VDE = 3.7 eV was measured by photoemission spectroscopy including corrections for surface scattering effects 47 ; and μ = 1.73 eV is a well-established position of the maximum in the measured optical absorption spectrum of the solvated electron 48 . The reorganization energy λ derived from the data of Fig.…”

Retrapping and solvation dynamics after femtosecond UV excitation of the solvated electron in water

“…2 Only the optical generation allows the direct observation of the fast processes in the femtosecond range during and after the build up of the solvated electron. In this way a large number of experiments on the generation of the solvated electron in water 3-7 and aqueous salt solutions 4,8-12 was performed.…”