Ultrafast formation of hydrated electrons in water at high concentration: Experimental evidence of the free electron

Plasma physics of liquids—A focused review

“…Moreover, the quasi-free electron lifetime is locally extended in the presence of a large number of excited electron states, an effect observed in Ref. 151 and attributed to the saturation of preexisting trapping states.…”

“…The lifetime of quasi-free electrons in water, for instance, is less than 1 ps, according to measurements and molecular dynamics simulations. [149][150][151] Figure 7 depicts a semiclassical interpretation of the solvation dynamics, where a conduction band electron first gets trapped at a weakly H-bonded OH group and subsequently decays to its stable solvation state. The fast solvation dynamics has formed the base of a second influential criticism on the electronic mechanism.…”

“…The experimental investigation of excess electrons in a liquid in a static field, for instance right below the threshold for plasma formation, can be performed with similar methods as applied in the absence of an external field. In these methods, the excess electrons are usually generated by means of radiolysis [164][165][166][167] or laser-induced ionization [150][151][152] with short beam pulses. The produced solvated or quasi-free electrons can be measured with synchronized optical methods, such as pump-probe transient absorption measurements, 159,168 timeresolved resonance Raman spectroscopy, 159 transient terahertz spectroscopy, 150 core-hole decay spectroscopy, 152 and the time-resolved optical interferometric technique described in Ref.…”

“…The produced solvated or quasi-free electrons can be measured with synchronized optical methods, such as pump-probe transient absorption measurements, 159,168 timeresolved resonance Raman spectroscopy, 159 transient terahertz spectroscopy, 150 core-hole decay spectroscopy, 152 and the time-resolved optical interferometric technique described in Ref. 151, as well as steady-state or time-resolved electron paramagnetic resonance spectroscopy. 169,170 The latter two techniques are able to detect solvated electrons in the form of radical pairs or radical-ion pairs, due to interaction with coexistent radicals or ions in the solution.…”

Picture of the wet electron: a localized transient state in liquid water

“…[23][24][25][26] The latter is a short-lived state, which is thought to form upon the trapping of the excess electron (e aq ) at defective water molecule sites, 27 likely where broken hydrogen bonds are present possibly due to thermal uctuations of the solvent. 23,24 When the trapping is ineffective, the e aq remains within the conduction states of the aqueous solvent, giving rise to a quasi-free electron 28 delocalized over distances of $40Å. 29 Building on spectroscopic observations, the following dynamics for the formation of the hydrated electron have been tentatively invoked.…”