Electron Solvation Dynamics Research Articles

Femtosecond Electron Solvation Kinetics in Water

Recent experimental and theoretical studies of electron solvation in liquid water have led to a detailed kinetic picture of this process. The electron solvation dynamics can be viewed as an excited state relaxation process between different electronic energy levels of the solvated electron. Simulations have suggested the importance of direct relaxation from upper excited electronic states as well as from the lowest excited electronic state (the wet electron state) to the ground electronic state. Using this as a model to analyze the experimental data, it is found that the quantum yield of wet electron formation cannot be less than 0.5 and that the peak of the wet electron absorption spectrum shifts to the IR with a decrease of wet electron formation quantum yield, with limiting values for the peak of 1.1−1.5 eV.

Primary Photochemical Processes in Water

The primary photochemical processes which occur in neat water after 282 nm high-intensity excitation via a two-photon mechanism were studied. Using probe pulses in UV, visible, and near-IR spectral ranges, the absorption process itself and the time evolution of the generated electrons and other photoproducts in the 0.1−80 ps scale were investigated. Different to previous femtosecond laser studies of water a quantitative analysis of the absorption process and yields of primary photoproducts was carried out. The two-photon absorption coefficient of liquid water for femtosecond pulses at 282 nm was measured to be β = (1.9 ± 0.5) × 10-12 m/W, while the quantum yield of the hydrated electron at the same wavelength was determined to be Φ (eaq-) = 0.11 ± 0.03. The results of the electron solvation and geminate recombination dynamics at 282 nm (excitation energy E2hν = 8.8 eV) are in accordance with the findings of other groups for different excitation wavelengths. The numerical simulations of our data suggest that the energy threshold for H2O+ ion formation is above 8.8 eV.

Microscopic model of electron solvation dynamics in polar liquids

Nous decrivons un modele microscopique de solvatation de l'electron dans un liquide polaire. L'electron est localise a l'interieur d'une cavite spherique. La dynamique de solvatation est representee par la contraction de la cavite. L'hydrodynamique est utilisee pour decrire le flux du solvant. La theorie variationnelle du polaron est utilisee pour calculer le changement d'energie libre lors du processus de contraction de la cavite. Nous predisons un temps de solvatation electronique dans l'eau en accord avec les resultats experimentaux. Nous fournissons une explication theorique au tres faible effet isotopique mesure pour la solvatation electronique dans l'eau.

Electron solvation dynamics in polar liquids

A hydrodynamic model of electron solvation in polar liquids is suggested. The electron is assumed to be localized within a spherical cavity in an ideal incompressible liquid. The solvation process is modelled by the contraction of the cavity size to its equilibrium value. The contraction dynamics are determined by the competition between the gain in electron-solvent interaction energy and increase in kinetic energy of the electron. An explicit expression for the timescale of the process is derived. Its dependence on the solvent density and polarity, external pressure and initial radius of the cavity is explored. The calculated timescale of the electron solvation in water is in agreement with experimental data. The theory predicts a small isotope effect (∼5%) on the electron solvation process in heavy water.

The role of solvent intramolecular modes in excess electron solvation dynamics

The role played by solvent molecular flexibility in the dynamics of the solvation of an initially energetically excited excess electron in water is investigated using nonadiabatic molecular dynamics simulation and a classical flexible water model. It is found that the effect of flexibility on relaxation times is substantial, but the effect on the branching ratio for excess electrons passing through alternative intermediate excited states is small. Examination of the optical absorption spectra of the hydrated electron shows that the effect of solvent flexibility is also small here. An analysis of transient spectra supports the validity of a kinetic analysis based on species with individual well defined signatures. However, the data suggest that a two state analysis of the dynamics neglects a potentially important role for early time delocalized electrons.

L'ion positif géminé intervient-il sur le destin de l'électron piégé incomplètement relaxé dans les liquides polaires irradiés?

A model is proposed concerning the influence of the parent positive ion on the fate of the incompletely relaxed trapped electron (eir−) in irradiated polar liquids. This model is based on the release, by a tunneling and (or) a trap-hopping mechanism in the Coulomb field of the cation, of the electrons captured in preexisting shallow localized states below the bottom of the conduction band of the solvent. The released electrons would either recombine with the parent positive ion or get retrapped. The net effect would be an accumulation of electrons in deeper traps. The removal of weakly trapped electrons would contribute to the decrease of the infrared part of the optical absorption spectrum during the very early time dynamics of electron solvation. Such a process would imply, as a consequence, the existence of a maximum of the eir− absorption spectrum.

Solvation dynamics of electron ejected by photoionization of p-phenylenediamine in several alcohols: temperature effect studied by picosecond transient absorption measurements

Solvation dynamics of electron ejected by photoionization of p-phenylenediamine in several alcohols: temperature effect studied by picosecond transient absorption measurements

Solvation dynamics of electrons ejected by picosecond dye laser pulse excitation of p-phenylenediamine in several alcoholic solutions

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSolvation dynamics of electrons ejected by picosecond dye laser pulse excitation of p-phenylenediamine in several alcoholic solutionsYoshinori. Hirata and Noboru. MatagaCite this: J. Phys. Chem. 1990, 94, 23, 8503–8505Publication Date (Print):November 1, 1990Publication History Published online1 May 2002Published inissue 1 November 1990https://doi.org/10.1021/j100386a004RIGHTS & PERMISSIONSArticle Views114Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (343 KB) Get e-Alerts

Femtosecond studies of electrons in liquids

Femtosecond time-resolved measurements were performed on the geminate recombination and solvation of electrons in liquids. The electrons were generated by multiphoton ionization in neat water and alkanes and by multiphoton detachment from Cl− and OH− ions in aqueous solution. For the neat liquids, the results are compared with the Onsager model of ion-pair recombination. An isotope effect is observed in the dynamics of both solvation and recombination in neat D2O relative to H2O. Studies with improved time resolution of electron solvation in neat water have measured the formation, decay, and absorption spectrum of the wet electron, i.e., the presolvated electron. By the discovery of an isosbestic wavelength, the formation of the wet electron is shown to involve two states; i.e., the transition is not continuous. The picture of the wet electron as an excited state of the solvated electron is presented. The differences in the solvation dynamics of electrons that are generated from neat water and from OH− and Cl− ions show that short-range molecular effects are important.

Equilibrium and nonequilibrium solvation and solute electronic structure

When a molecular solute is immersed in a polar and polarizable solvent, the electronic wave function of the solute system is altered compared to its vacuum value; the solute electronic structure is thus solvent-dependent. Further, the wave function will be altered depending upon whether the polarization of the solvent is or is not in equilibrium with the solute charge distribution. More precisely, while the solvent electronic polarization should be in equilibrium with the solute electronic wave function, the much more sluggish solvent orientational polarization need not be. We call this last situation “non-equilibrium solvation.” We outline a nonlinear Schrödinger equation approach to these issues. The nonlinearity arises from the self-consistent aspect that the solute electronic Hamiltonian depends on the solvent electronic polarization which is induced by the solute charge distribution. We illustrate the predictions of the theory for electron transfer reactions, ionic dissociations, and solvation dynamics in polar solvents. Special features of interest include activation barriers that differ markedly from standard predictions, and novel solvent dynamical features.

Dynamics of excess electron migration, solvation, and spectra in polar molecular clusters

The dynamics of excess electron localization, migration, and solvation in water and ammonia clusters, and the time-resolved spectroscopic consequences of these processes, are investigated via computer simulations. In these simulations, the solvent evolves classically and the electron propagates in the ground state. The coupling between the polar molecular cluster and the electron is evaluated via the quantum expectation value of the electron–molecule interaction potential. Starting from an electron attached to a cold molecular cluster in a diffuse weakly bound surface state, temporal stages of the electron solvation and migration processes, leading to the formation of an internally solvated state, and the associated variations in the excitation spectra are described. The migration of the excess electron during the penetration is characterized by a nonhopping, polaronlike mechanism.

Dynamics of electron localization, solvation, and migration in polar molecular clusters.

The time evolution of electron localization, migration, and solvation in water and ammonia clusters is investigated via computer simulations. The attachment of an electron to a cold molecular cluster in a diffuse weakly bound surface state, the dynamics of solvation, the nonhopping mechanism of migration leading to the formation of an internally solvated state, and the spectral manifestation of these processes are demonstrated.

Femtosecond molecular motions and implications for electron solvation dynamics in liquids

Molecular motions at femtosecond times are observed experimentally, via nonlinear laser spectroscopy, as responses to the imposition of a sudden, intense laser field in the optical Kerr effect. The electronic, librational, collision-induced translational and reorientational diffusional motions identified through the nonlinear polarizability responses are linked to the probable responses of the disordered medium to an excess electron undergoing multiple scattering at times <10 -12s.

Femtosecond reactivity of electron in aqueous solutions

Femtosecond optical techniques allowing the generation of intense optical pulses from the near ultraviolet to the near infrared are used in the monitoring of ultrafast photophysical and photochemical reactions in aqueous solutions. Selected examples for dynamics of electron solvation in water and aqueous solution of ferrocyanide are discussed.

Influence of Viscous Media on Charge Transfer Reactions

The influence of viscous H2O‐Dextran media on two charge transfer reactions has been investigated using laser photolysis coupled with pico and nanosecond time resolved absorption spectroscopy.In the first case, a charge‐transfer reaction from a solute (potassium ferrocyanide) to the solvent was studied and the electron solvation dynamics was followed. A solvation time delay, depending on the polymer concentration, is observed which indicates that electrons remain quasi‐free for longer periods in these media.In the second case, the quenching process of the triplet state of an excited metallo porphyrin(ZnP4+) by an electron acceptor, methylviologen chloride (MV2+, 2 Cl–) is studied. The measured triplet quenching rate constant values decrease with increasing dextran concentration, but remain higher than those calculated, taking into account a simple viscosity effect. This result is explained in terms of a competition between a decay of the diffusion rate constants of (ZnP4+)* and MV2+ due to a viscosity effect and an enhanced cage effect around the ions (ZnP4+*, MV2+). Once formed, this last effect favours the charge transfer reaction.

Femtosecond electron solvation in micellar solutions: Application to one-electron transfer kinetic in the univalent reduction of a coenzyme

Femtosecond UV pulses are used to generate solvated electrons and then initiate the univalent reduction of an oxidized coenzyme (βNAD+). These phenomena are monitored, at the same femtosecond level, by time-resolved absorption spectroscopy techniques. These experiments show that the subpicosecond dynamics of electron solvation in the polar water bulk of micellar solutions is strongly dependent on the nature and the type of micelles forming the surfactant. In deoxygenated aqueous micelles, the charged micellar surface prevents the reverse electron transfer with cationic radical (PTH+) entrapped in the nonpolar inner core. Univalent reduction of oxidized nicotinamide adenine dinucleotide (βNAD+). by one-electron transfer reaction with a time constant of 270 ps has been observed implying that this coenzyme has retained its ability to mediate electron transfer when solubilized in the semirigid environment of the polar water bulk of aqueous micelles.

Dynamics of electron solvation in the n-propanol-3-methylpentane system at low temperature

The dynamics of electron solvation in n-propanol-3-methylpentane system have been investigated. Some correspondence between solvation time, τ s and the relaxation time for hydrogen bond breaking, τ 1 was found.

Dynamics of electron solvation in liquid water

The absorption of the solvated electron was measured to appear less than 0.3 ps after photolysis of aqueous ferrocyanide solutions with subpicosecond ultraviolet pulses This upper limit for the electron solvation tine in water suggests a mechanism involving pre-existing deep traps, rather than known mechanisms requiring molecular reorientation.

Molecular relaxation processes in very dilute systems: A 13C NMR study of alcohols in alkanes

13C T 1 relaxation times have been determined for n-butanol in C 6D 12 in the concentration range 0.001 ⩽ x ⩽ 1 (using 13C labelled alcohol) and for t-butanol in the range 0.01 ⩽ x ⩽ 1. In the former case, this has allowed us to probe molecular mobility down to the region of monomeric alcohols. Comparison with previous results from measurements of 1H chemical shifts, dielectric relaxation, and the picosecond dynamics of electron solvation allows us to build up a detailed picture of molecular clustering and liquid structure in alkane—alcohol mixtures. For n-butanol, the local liquid structure is established by x = 0.2 while t-butanol does not appear to form aggregates larger than trimers until x = 0.5.

13C NMR studies of molecular relaxation processes in polar fluids

A study of the dynamical molecular structure of a dilute polar fluid is reported, in which 13C spin-lattice relaxation times of decanol in deuterated cyclohexane are presented for the individual carbon atoms, and the results are discussed in the context of viscosity data of decanol in alkane systems. The two techniques provide complementary information about the mobility of the alcohol chains and the onset of multimer formation, which is also pertinent to the dynamics of electron solvation in the same systems.