Time-resolved spectroscopy of solvated electrons

The theory of time-dependent transient spectra of solvated electrons is developed. It is shown that the evolution of the spectral line centre reproduces the time dependence of the classical correlation function of the random process of electronic energy level fluctuations. The results of this investigation are compared with experiment.     

Compton profiles of solvated electrons

The importance of applying a variety of experimental techniques to unravel the nature of solvated electrons is emphasized. Compton profiles are evaluated for these species from a range of models. Some comparisons are made with positron annihilation studies.     

Spectral moments of solvated electrons

A moment theory analysis is performed on the optical absorption spectra of surplus electrons localized in various media. The deduced attributes of the excess particle are compared with those obtained by a perturbation treatment of the exact ground state solution of a currently popular model potential for the species. Several frequency dependent observables are evaluated and a source of inadequacy in the current theory, the presence of a Coulomb tail, is revealed.     

Cleavage of carbon-carbon-bonds by solvated electrons

Benzylic C-C bonds in diarylmethanes and diarylethanes (Ar = phenyl, naphthyl) are cleaved by potassium in dimethoxyethane/octaglyme.     

Photo-detrapping of solvated electrons in an ionic liquid

We studied the dynamics of photo-detrapped solvated electrons in the ionic liquid trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) using laser flash photolysis. The solvated electrons were produced by the electron photodetachment from iodide via a 248 nm KrF excimer laser. The solvated electron decayed by first-order kinetics with a lifetime of about 240 ns. The spectrum of the solvated electron in the ionic liquid TMPA-TFSI is very broad with a peak around 1100 nm. After the 248 nm pulse, a 532 nm pulse was used to subsequently detrap the solvated electrons. After the detrapping pulse, quasi-permanent bleaching was observed. The relative magnitude of the bleaching in the solvated electron absorbance was measured from 500 to 1000 nm. The amount of bleaching depends on the probe wavelength. The fraction of bleached absorbance was larger at 500 nm than that at 1000 nm, suggesting that there are at least two species that absorb 532 nm light. We discuss the present results from viewpoint of the heterogeneity of ionic liquids.     

Electrochemical generation of solvated electrons from nanostructured carbon

Voltammograms for electrodes fabricated of nanostructured carbon of various morphology (nanotube paper, columnar and filament structures) in hexamethylphosphoric triamide (HMPA) solution have been obtained and analysed. Intensive dark-blue coloration near cathode surface at potentials as low as E ∼ −1.2 V (s.c.e.) has been observed. An ESR (electron spin resonance) spectrum of this frozen dark-blue solution was recorded. This spectrum coincides with one of free electrons. Experimental proofs of the existence of electron emission into electrolytic solutions at moderate cathodic potentials are present for all electrodes. This effect is established to be connected with the presence of atomically sharp areas on the electrode surfaces.     

Resonance Raman spectra of electrons solvated in liquid alcohols

Resonance Raman spectra of electrons solvated in liquid methanol, ethanol, and n-propanol are presented. At least five distinct solvent modes exhibit resonantly enhanced scattering, including the OH torsion, CO/CC stretches, the OH in-plane bend, methyl deformations, and the OH stretch. The 200-350 cm-1 frequency downshift of the OH stretch indicates a strong H-bond interaction between the electron and the hydroxyl group. The multiple modes including alkyl vibrations that are coupled to the electronic transition of the solvated electron reveal the extension of the electron's wavefunction into the alkyl solvent environment.     

The absorption coefficient of a polar liquid with solvated electrons

An equation for the absorption coefficient of a polar liquid with excess (solvated) electrons is derived. It is taken into account that (1) each excess electron can for a certain time reside on only one liquid molecule (during this time, the molecule is in the anion-resonance state), and (2) a polar liquid is electrostatically nonuniform because it has different local potentials, which can be calculated for each molecule. The probabilities of quantum movements of excess electrons in a liquid from one molecule to another caused by the absorption of photons are considered.     

Time-resolved photoelectron spectroscopy of solvated electrons in aqueous NaI solution

Time-resolved photoelectron spectroscopy was used to study the energetics and dynamics of solvated electrons in aqueous solution. Solvated electrons are generated by ultrafast photodetachment in a 100 mM aqueous NaI solution. Initially, an ensemble of strongly bound ("cold") solvated electrons and an ensemble of weakly bound ("hot") electrons in an unequilibrated solvent environment are observed. We report an ultrafast recombination channel for the "hot" electrons with a rate of (800 fs)(-1) which is in competition with thermalization occurring with a rate of (1.1 ps)(-1). The thermalized electrons recombine with the iodide radical with a rate of (22 ps)(-1). About 35% of the thermalized electrons escape geminate recombination and form free, solvated electrons. The vertical detachment energy for the solvated electron is determined to be 3.40 eV. No indication for a surface-bound electron at lower binding energies was observed.     

Stability of InP oxide versus solvated electrons in liquid ammonia

In alkaline aqueous medium (pH 9), potassium ferricyanide was used as an oxidizing agent on InP. This electroless process was successfully controlled by capacity measurements, AFM and XPS analyses. For the first time, the chemical stability of the oxide has been studied against the strongest reducing agent in liquid ammonia (?50 °C): the solvated electron. It was obtained in two ways; an electroless process which involved the addition of metallic potassium and by cathodic galvanostatic treatment on InP in neutral medium. As a first result, the electroless process required a strong rinsing step of the surface by pure liquid ammonia. As a second result, the galvanostatic process gave also promising results. A significant decrease of the amount of oxide was evidenced by capacity measurements, AFM and XPS analyses.     

Femtosecond relaxation dynamics of solvated electrons in liquid ammonia.

The ultrafast relaxation dynamics of the well-known solvated electron in liquid ammonia solutions are investigated with femtosecond near-infrared pump-probe absorption spectroscopy. Immediately after photoexcitation, the dynamic absorption spectrum of the electron is substantially red-shifted with respect to its stationary spectrum. A subsequent dynamic blue shift of the pump-probe spectrum occurs on a timescale of 150 fs. The data are understood in terms of ground-state "cooling" and can be quantitatively simulated by an intuitive temperature-jump model employing a dynamically evolving Kubo line shape for the electronic resonance. A simple estimate implies that, on average, the electron in the liquid is coordinated to six nearest-neighbor ammonia molecules. An equivalent analysis of the data based on a bubble-formation/cavity-contraction mechanism is briefly outlined.     

Reactivity between biphenyl and precursor of solvated electrons in tetrahydrofuran measured by picosecond pulse radiolysis in near-ultraviolet, visible, and infrared

The initial decrease of solvated electrons in tetrahydrofuran (THF) upon addition of biphenyl was investigated by picosecond pulse radiolysis. Transient absorption spectra derived from the biphenyl radical anion (centered at 408 and 655 nm) and solvated electrons of THF (infrared) were successfully measured in the wavelength region from 400 to 900 nm by the extension of a femtosecond continuum probe light to near-ultraviolet using a second harmonic generation of Ti:sapphire laser and a CaF2 plate. From the analysis of kinetic traces at 1300 nm considering the overlap of primary solvated electrons and partial biphenyl radical anion, C37, which is defined by the solute concentration to reduce the initial yield of solvated electrons to 1/e, was found to be 87 +/- 3 mM. The rate constant of solvated electrons with biphenyl was determined as 5.8 +/- 0.3 x 10(10) M(-1) s(-1). We demonstrate that the kinetic traces at both 408 nm mainly due to biphenyl radical anion and 1300 nm mainly due to solvated electrons are reproduced with high accuracy and consistency by a simple kinetic analysis. Much higher concentrations of biphenyl (up to 2 M) were examined, showing further increase of the initial yield of biphenyl radical anion accompanying a fast decay component. This observation is discussed in terms of geminate ion recombination, scavenging, delayed geminate ion recombination, and direct ionization of biphenyl at high concentration.     

Electrogenerated chemiluminescence with solvated electrons in hexamethylphosphoroamide (HMPA)

The electrogenerated chemiluminescence of N-toluenesulfonyl carbazole, 9-chlorofluorene derivatives and N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) with solvated electrons in HMPA are discussed. The fairly bright emissions occurred simultaneously when solvated electrons were generated electrochemically. In the case of N-toluenesulfonyl carbazole and 9-chlorofluorene derivatives, the respective carbanions formed by “dissociative electron transfer reactions” are the fluorescents. The singlet state of TMPD seems to be directly formed by the electron transfer reactions between radical cations of TMPD and solvated electrons.     

Moving solvated electrons with light: nonadiabatic mixed quantum/classical molecular dynamics simulations of the relocalization of photoexcited solvated electrons in tetrahydrofuran (THF)

Motivated by recent ultrafast spectroscopic experiments [Martini et al., Science 293, 462 (2001)], which suggest that photoexcited solvated electrons in tetrahydrofuran (THF) can relocalize (that is, return to equilibrium in solvent cavities far from where they started), we performed a series of nonequilibrium, nonadiabatic, mixed quantum/classical molecular dynamics simulations that mimic one-photon excitation of the THF-solvated electron. We find that as photoexcited THF-solvated electrons relax to their ground states either by continuous mixing from the excited state or via nonadiabatic transitions, approximately 30% of them relocalize into cavities that can be over 1 nm away from where they originated, in close agreement with the experiments. A detailed investigation shows that the ability of excited THF-solvated electrons to undergo photoinduced relocalization stems from the existence of preexisting cavity traps that are an intrinsic part of the structure of liquid THF. This explains why solvated electrons can undergo photoinduced relocalization in solvents like THF but not in solvents like water, which lack the preexisting traps necessary to stabilize the excited electron in other places in the fluid. We also find that even when they do not ultimately relocalize, photoexcited solvated electrons in THF temporarily visit other sites in the fluid, explaining why the photoexcitation of THF-solvated electrons is so efficient at promoting recombination with nearby scavengers. Overall, our study shows that the defining characteristic of a liquid that permits the photoassisted relocalization of solvated electrons is the existence of nascent cavities that are attractive to an excess electron; we propose that other such liquids can be found from classical computer simulations or neutron diffraction experiments.     

Determination of the characteristics of solvated electrons from optical absorption data

As difficulties are encountered with model theories in describing the nature of solvated electrons, it is suggested that possible non-model relations in the theory of solvated electrons be used. In the present work the results that follow from the sum rules, virial theorem and threshold formulae of the quantum theory of scattering are examined. In this way it is possible to establish relationships that can be used for determining some of the physical characteristics of solvated electrons directly from optical data.     

Low temperature reaction of aromatic hydrocarbons with ethylene and solvated electrons

A wide variety of aromatic hydrocarbons can be ethylated at benzylic and aromatic positions by treatment with ethylene and potassium in glyme/octaglyme at ?25°C.     

A method for the generation of solvated electrons in polar solvents

A simple method for generating solvated electrons in a polar liquid by a rapid discharge of a capacitor bank is suggested. New theoretical concepts of excess electrons in polar liquids are used.