Localization Of Excess Electron Research Articles

Excess Electron Localization in Solvated DNA Bases

We present a first-principles molecular dynamics study of an excess electron in condensed phase models of solvated DNA bases. Calculations on increasingly large microsolvated clusters taken from liquid phase simulations show that adiabatic electron affinities increase systematically upon solvation, as for optimized gas-phase geometries. Dynamical simulations after vertical attachment indicate that the excess electron, which is initially found delocalized, localizes around the nucleobases within a 15 fs time scale. This transition requires small rearrangements in the geometry of the bases.

Theoretical study of the localization of excess electrons at the surface of ice

The localization of excess electrons at the basal plane surface of hexagonal ice Ih isinvestigated theoretically, combining density functional theory (DFT) with a partialself-interaction correction (SIC) scheme, to account for spurious self-interactioneffects that artificially delocalize the excess electrons. Starting from energeticallyfavored surface geometries, we find strong localization of excess electrons at surfacedangling bonds, in particular for surface adsorbed water monomers and dimers.

Electron hydration energy: Nonempirical estimate

Based on the results of quantum chemical calculations, the energies of vertical (photoionization) electron removal from superficial and bulk water layers are estimated as 2.9 and 4.4 eV respectively. For the first time, a nonempirical estimate of the electron hydration energy is obtained, 2.6 eV, which characterizes the electron state both at the superficial and bulk hydration. To find these value, molecular cluster systems modeling the Bjerrum defects of the hydrogen-bond network of water localizing the additional electron were calculated. Typical ways of the reorganization of defects upon the electron removal are identified. Conditions under which the relaxation of defects is reversible upon the re-addition of the charge are determined. The pre-existence of defects is shown not to be an indispensable condition of the effective localization of excess electrons by water. Small distortions, as well as breakage, of the continuity of the hydrogen-bond network are sufficient.

Excess electron kinetics by dispersive conductivity: A proposition

A proposition for the simultaneous experimental determination of mobility and scavenger rate coefficient of localized excess electrons is exposed. Based on an earlier theory [Schiller, R., Balog, J., Nagy, G., 2005. Continuous-time random-walk theory of interfering diffusion and chemical reaction with an application to electrochemical impedance spectra of oxidized Zr–1%Nb. J. Chem. Phys. 123, 094704-1-7], it is expected that the steady state conductivity of an insulating liquid, irradiated or illuminated in the presence of some scavenger, depends on frequency. By analyzing the frequency dependence one can obtain the values of the above material properties.

Direct dynamics simulations of photoexcited charge-transfer-to-solvent states of the I −(H 2O) 6 cluster

Direct molecular dynamics simulations have been carried out to understand the relaxation dynamics of photoexcited charge-transfer-to-solvent (CTTS) states for the I −(H 2O) 6 cluster and the subsequent excess electron stabilization dynamics by solvent molecules. Due to a small singlet–triplet splitting, the lowest triplet potential energy surface at the B3LYP-level calculations was used to model the CTTS singlet excited-state surface. Two book-type structures, which correspond to the lowest ground-state minimum-energy geometries, were vertically excited with the initial kinetic energy being zero. Although these two structures have a very similar geometry, it was found that the excess electron localization dynamics was totally different.

Excess Electrons Stabilized on Ionic Oxide Surfaces

Surface excess electrons are remarkable chemical entities that provide great opportunities for the design of new materials with precisely tuned electronic and magnetic properties. In this Account, we describe the structure and electronic properties of excess electron centers generated at the surface of insulating oxides. We also outline the elementary mechanisms that are at the basis of the generation of excess electrons at solid surfaces, setting a comparison to the general problem of excess electron localization in condensed media. Emphasis is given to morphological aspects relative to the surface-trapping sites as deduced from combined electron paramagnetic resonance and accurate quantum chemical calculations. The remarkable reactivity featured by the so formed "electron-rich" surfaces is illustrated, describing the reduction of simple diatomic molecules that form adsorbed radical anions via direct surface to adsorbate electron transfer.

Excess electron localization sites in neutral water clusters

We present approximate pseudopotential quantum-mechanical calculations of the excess electron states of equilibrated neutral water clusters sampled by classical molecular dynamics simulations. The internal energy of the clusters are representative of those present at temperatures of 200 and 300 K. Correlated electronic structure calculations are used to validate the pseudopotential for this purpose. We find that the neutral clusters support localized, bound excess electron ground states in about 50% of the configurations for the smallest cluster size studied (n = 20), and in almost all configurations for larger clusters (n > 66). The state is always exterior to the molecular frame, forming typically a diffuse surface state. Both cluster size and temperature dependence of energetic and structural properties of the clusters and the electron distribution are explored. We show that the stabilization of the electron is strongly correlated with the preexisting instantaneous dipole moment of the neutral clusters, and its ground state energy is reflected in the electronic radius. The findings are consistent with electron attachment via an initial surface state. The hypothetical spectral dynamics following such attachment is also discussed.

Ab initio Study of [Mg,nH2O]‐ Reactive Decay Products: Structure and Stability of Magnesium Oxide and Magnesium Hydroxide Water Cluster Anions [MgO,(n—1)H2O]‐, [HMgOH,(n—1)H2O]‐ and [Mg(OH)2,(n—2)H2O]‐

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Ab initio study of [Mg,nH2O]−reactive decay products: structure and stability of magnesium oxide and magnesium hydroxide water cluster anions [MgO,(n − 1)H2O]−, [HMgOH,(n − 1)H2O]−and [Mg(OH)2,(n − 2)H2O]−

Geometrical as well as electronic structures of hydrated magnesium oxide and hydroxide anions with the stoichiometry [MgO,(n − 1)H2O]−, [HMgOH,(n − 1)H2O]− and [Mg(OH)2,(n − 2)H2O]− are investigated by ab initio calculations at the MP2 level of theory. Different structural archetypes emerge and the excess electron localization modes within them are elucidated. The oxidation state of the central Mg atom is found to correlate with the coordination number, which exhibits a strong influence on the localization mode of the excess electron. Only in [HMgOH,(n − 1)H2O]−, n = 1–2, and [Mg(OH)2,(n − 2)H2O]− , n = 2–3, a valence bound state of the excess electron is favored, whereas for all larger cluster sizes the excess electron resides within the hydration shell and is localized by dangling O–H bonds. These act as molecular tweezers which trap the hydrated electron. The investigated magnesium oxide and hydroxide water cluster anions are discussed as potential products of a reactive decay of anionic magnesium water clusters [Mg,nH2O]−, elucidating the chemical reactivity of these species. The minimum energy pathway of the O–H insertion by Mg in [Mg,nH2O]− is investigated in detail.

Excess electron transport in cryoobjects

Experimental results on excess electron transport in solid and liquid phases of Ne, Ar, and solid N2–Ar mixture are presented and compared with those for He. The muon spin relaxation technique in frequently switching electric fields was used to study the phenomenon of delayed muonium formation: excess electrons liberated in the μ+ ionization track converge upon the positive muons and form Mu (μ+e−) atoms. This process is shown to be crucially dependent upon the electron’s interaction with its environment (i.e., whether it occupies the conduction band or becomes localized in a bubble of tens of angstroms in radius) and upon its mobility in these states. The characteristic lengths involved are 10−6–10−4 cm, and the characteristic times range from nanoseconds to tens of microseconds. Such a microscopic length scale sometimes enables the electron to spend its entire free lifetime in a state which may not be detected by conventional macroscopic techniques. The electron transport processes are compared in: liquid and solid helium (where the electron is localized in a bubble); liquid and solid neon (where electrons are delocalized in the solid, and the coexistence of localized and delocalized electron states in the liquid was recently found); liquid and solid argon (where electrons are delocalized in both phases); orientational glass systems (solid N2–Ar mixtures), where our results suggest that electrons are localized in an orientational glass. This scaling from light to heavy rare gases enables us to reveal new features of excess-electron localization on a microscopic scale. Analysis of the experimental data makes it possible to formulate the following tendency of the muon end-of-track structure in condensed rare gases. The muon–self-track interaction changes from isolated-pair (muon plus the nearest track electron) in helium to multipair (muon in the vicinity of tens of track electrons and positive ions) in argon.

Ultrafast dynamics of excess electrons in a molten salt: Femtosecond investigation of K–KCl melts

Pump–probe studies of localized excess electrons in liquid KCl have been performed at probe wavelengths between 600 and 1530 nm at elevated temperatures. After photoexcitation with 50 fs pulse centred at 800 nm a transient bleach is observed at wavelengths between 600 and 1245 nm while at wavelengths longer than 1300 nm only a transient absorption is observed. The transient bleach recovery can be assigned to the lifetime of strongly localized electrons (F-centres) and represents ground state dynamics with a time constant of (200 ± 50) fs, in reasonable agreement with theoretical calculations for polaron-like states in liquid K–KCl. The transient absorption at longer wavelengths, that decays with the same time constant, might be due to weakly localized electrons. Consequently, the ionic motion of the alkali halide melt determines the dynamics in this system. These investigations represent the first direct ultrafast study with fs time resolution of localized electrons in the molten K–KCl sytems.

Ab initio treatment of magnesium water cluster anions [Mg,nH2O]−, n ≤ 11

Geometrical as well as electronic structures of magnesium water cluster anions with the formal stoichiometry [Mg,nH2O]−, n≤11, are investigated through application of various correlated ab initio methods. Different structural archetypes emerge and the excess electron localization mode within them are elucidated. Their stability against electron detachment are predicted through calculation of vertical and adiabatic detachment energies of the most stable cluster geometries. Minimum cluster sizes of vertically and adiabatically stable [Mg,nH2O]− clusters are discussed. The impact of the excess electron on cluster structures is explored and the extent of the cluster structure reorganization upon electron detachment in [Mg,nH2O]− is quantified.

Structural Dependence of Electron Transfer to Non‐Covalent Polar Complexes

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Excess electron transport and delayed muonium formation in condensed rare gases

Experimental studies of excess electron transport in solid and liquid phases of Ne and Ar are presented and compared with those for He. The technique of muon spin relaxation in frequently reversed electric fields was used to study the phenomenon of delayed muonium formation, whereby excess electrons liberated in the ${\ensuremath{\mu}}^{+}$ ionization track converge upon the positive muons and form ${\ensuremath{\mu}}^{+}{e}^{\ensuremath{-}}$ atoms. This process is shown to be crucially dependent upon the electron's interaction with its environment (i.e., whether it occupies the conduction band or becomes localized) and upon its mobility in these states. The characteristic lengths involved are ${10}^{\ensuremath{-}6}$ to ${10}^{\ensuremath{-}4} \mathrm{cm};$ the characteristic times range from nanoseconds to tens of microseconds. Such a microscopic length scale sometimes enables the electron to spend its entire free lifetime in a state which may not be detected by conventional macroscopic techniques. The end-of-track processes are compared in (i) liquid and solid helium (where the electron is known to be localized in a bubble in the liquid phase and is thought to behave in a similar manner in the solid); $(\mathrm{ii})$ liquid and solid neon (where both localized and bandlike electrons are found in the liquid phase while most are delocalized in the solid); and $(\mathrm{iii})$ liquid and solid argon (where most electrons are bandlike in both phases). This scaling from light to heavy rare gases enables us to demonstrate new features of excess electron localization on the microscopic scale and provides insight into the structure of the end of the muon track in condensed rare gases.

Structural dependence of electron transfer to non-covalent polar complexes.

Electron attachment to polar molecules and their non-covalent complexes can lead to different kinds of anions which differ from their excess electron localization. Spectroscopic methods for studying anion structures are reviewed. In many cases, the neutral and anion structures are identical and can be deduced from the electron attachment properties. Examples are given for complexes containing polar solvents or building blocks of biomolecules (nucleobases, amino acid residues...).

Computer simulation of water and concentrated ionic solutions. Potential fluctuations and electron localization

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article Bartczak Witold M., Kroh Jerzy, Zapalowski Michal and Pernal Katarzyna 2001Computer simulation of water and concentrated ionic solutions. Potential fluctuations and electron localizationPhil. Trans. R. Soc. A.3591593–1609http://doi.org/10.1098/rsta.2001.0867SectionRestricted accessComputer simulation of water and concentrated ionic solutions. Potential fluctuations and electron localization Witold M. Bartczak Witold M. Bartczak Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Department of Theoretical Chemistry, University of Lodz, Pomorska 149/153, 90–236 Lodz, Poland () Google Scholar Find this author on PubMed Search for more papers by this author , Jerzy Kroh Jerzy Kroh Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Google Scholar Find this author on PubMed Search for more papers by this author , Michal Zapalowski Michal Zapalowski Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Google Scholar Find this author on PubMed Search for more papers by this author and Katarzyna Pernal Katarzyna Pernal Google Scholar Find this author on PubMed Search for more papers by this author Witold M. Bartczak Witold M. Bartczak Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Department of Theoretical Chemistry, University of Lodz, Pomorska 149/153, 90–236 Lodz, Poland () Google Scholar Find this author on PubMed Search for more papers by this author , Jerzy Kroh Jerzy Kroh Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Google Scholar Find this author on PubMed Search for more papers by this author , Michal Zapalowski Michal Zapalowski Institute of Applied Radiation Chemistry, Technical University of Lodz, Wroblewskiego 15, 93-590 Lodz, Poland Google Scholar Find this author on PubMed Search for more papers by this author and Katarzyna Pernal Katarzyna Pernal Google Scholar Find this author on PubMed Search for more papers by this author Published:15 August 2001https://doi.org/10.1098/rsta.2001.0867AbstractThe possibilities of trapping an excess electron by potential traps in liquid water and aqueous ionic solutions have been investigated by means of a computer simulation method.The equilibrium configurations of water molecules are generated by the molecular dynamics (MD) method and the molecular configurations are searched for local minima of the potential energy. The analysis of a large set of the minima allows us to obtain an extensive statistical description of the microscopic trapping sites. The estimated concentration of the electron traps in liquid water is ca. 0.5 mol dm–3.The possibility of electron trapping depends very strongly on the lifetime of the potential traps. The simulations yielded the distribution of the trap lifetime with an average of 84 fs. A substantial fraction (20%) of the traps live longer than 100 fs, a small fraction (0.2%) live as long as 1 ps. These values can be compared with experimental measurements of the electron hydration time of the order of 100 fs.The calculations of the localized excess electron in concentrated solutions of LiCl and NaCl have been performed. The MD simulations of the solutions provided an ensemble of configurations of ions and water molecules. The quantum calculations (based on density functional theory, non–local version) of an excess electron in the clusters of ions and water molecules extracted from the MD configurations have been performed for a few hundred cases. It appears that most of the hydrated Li+ cations can trap an excess electron. The histograms of the distribution of energy of the HOMO orbitals and a histogram of the electron excitation spectrum have been constructed. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetails This Issue15 August 2001Volume 359Issue 1785Theme Issue ‘Structures of water and aqueous solutions‘ compiled by M. C. R. Symons Article InformationDOI:https://doi.org/10.1098/rsta.2001.0867Published by:Royal SocietyPrint ISSN:1364-503XOnline ISSN:1471-2962History: Published online15/08/2001Published in print15/08/2001 License: Citations and impact Keywordselectron localizationwatercomputer simulationpotential trapsionic solutions

Muonium formation in condensed neon and argon

We review our studies of atomic muonium formation under the influence of applied electric fields in condensed Ne and Ar. The comparison of muonium formation processes in solid neon, where electrons are delocalized, liquid neon, where the coexistence of delocalized and localized electrons was found recently, and condensed Ar, where electrons are delocalized in both phases, brings a new understanding of excess electron localization on a microscopic scale.

Electronic isomers in [(CO2)nROH]− cluster anions. II. Ab initio calculations

Ab initio MO calculations have been performed for the [(CO2)nROH]− (R=H and CH3) anions with n=1 and 2. Three stable structures are found for [(CO2)H2O]−, and two structures for [(CO2)CH3OH]−. All the [(CO2)ROH]− structures are characterized by the charge localization on the CO2 moiety, which interacts with ROH through an O–H⋯O linkage. It is also revealed that the addition of ROH to CO2− leads to the formation of a potential barrier against autodetachment higher than that of a bare CO2−, which results in the increasing stability of [(CO2)ROH]− species. For n=2 the calculations predict the existence of two types of isomers having different degrees of the excess electron localization: CO2−⋅ROH(CO2) and C2O4−⋅ROH isomers. These “electronic isomers” are calculated to be close in energy, while their calculated vertical detachment energies (VDEs) differ by more than 1 eV. The ab initio results are discussed in comparison with recent experimental ones derived from photoelectron spectra of [(CO2)nROH]−.

Photodetachment of small water cluster anions in the near-infrared through the visible region

Water cluster anions were efficiently generated by attachment of slow photoelectrons ejected from laser-excited zirconium metal surface, and photodetachment cross sections for (H 2O) n − ( n=2, 6, 7, and 11) were measured for a photon energy range of 0.74–2.54 eV. A gradual decrease of the cross section with the photon energy was observed for all the species. It was also found that the larger cluster exhibits the larger cross section. Size-dependent features of the spectra were discussed in relation to the excess electron localization with evolution of the cluster size.

Dynamics of Excess Electron Localization in Liquid Helium and Neon

In this paper, we address the relations between the structure, electronic level structure, energetics, and localization dynamics of an excess electron in a bubble in liquid 4He, 3He, and Ne. Our treatment of the dynamics of formation for the electron bubble rests on a quantum mechanical Wigner−Seitz description of the excess electron in conjunction with a hydrodynamic picture for the liquid. The dynamics of electron localization is described in terms of the initial formation of an incipient bubble of radius 3.3−3.5 Å followed by adiabatic bubble expansion in the ground electronic state. The hydrodynamic model for bubble expansion considers the expansion of a spherical cavity in an incompressible liquid with the energy dissipation being due to the emission of sound waves. This model predicts the bubble expansion time ( ) in liquid 4He to be = 8.5 ps at P = 0, exhibiting a marked pressure dependence (decreasing by a numerical factor of 4 at P = 16 atm) and revealing a small isotope effect of (4He)/ (3He) = 0.83 in liquid 3He, while for liquid Ne, ≅ 1 ps. The collapse times of the empty bubble formed by vertical photoionization of the electron bubble are τc = 19.8 ps for 4He and τc = 34 ps for 3He, with τc being considerably longer than , reflecting the effect of the kinetic electron energy on the fast electron bubble expansion. The interrogation of the electron bubble localization dynamics by femtosecond absorption spectroscopy is explored by the analysis of the temporal evolution of the electronic excitation energies.