Moment analysis of hydrated electron cluster spectra: Surface or internal states?

Bartels, David M.

doi:10.1063/1.1391476

Cited by 70 publications

(116 citation statements)

References 16 publications

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“…24 Instead, they proposed that the spectroscopy of the hydrated electron was more consistent with a solvent−anion complex, 24 a structure which shares many features in common with the LGS simulations. 15 Indeed, moment analysis of the hydrated electron's absorption spectrum tells us that the hydrated electron's charge density has a radius of gyration of 2.4 Å, 25 but nothing in the spectrum directly indicates whether the water molecules are primarily inside or outside of the charge density.…”

Section: ■ Controversy Over Hydrated Electron MD Simulationsmentioning

confidence: 99%

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To Be or Not to Be in a Cavity: The Hydrated Electron Dilemma

2013

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The hydrated electronthe species that results from the addition of a single excess electron to liquid waterhas been the focus of much interest both because of its role in radiation chemistry and other chemical reactions, and because it provides for a deceptively simple system that can serve as a means to confront the predictions of quantum molecular dynamics simulations with experiment. Despite all this interest, there is still considerable debate over the molecular structure of the hydrated electron: does it occupy a cavity, have a significant number of interior water molecules, or have a structure somewhere in between? The reason for all this debate is that different computer simulations have produced each of these different structures, yet the predicted properties for these different structures are still in reasonable agreement with experiment. In this Feature Article, we explore the reasons underlying why different structures are produced when different pseudopotentials are used in quantum simulations of the hydrated electron. We also show that essentially all the different models for the hydrated electron, including those from fully ab initio calculations, have relatively little direct overlap of the electron’s wave function with the nearby water molecules. Thus, a non-cavity hydrated electron is better thought of as an “inverse plum pudding” model, with interior waters that locally expel the surrounding electron’s charge density. Finally, we also explore the agreement between different hydrated electron models and certain key experiments, such as resonance Raman spectroscopy and the temperature dependence and degree of homogeneous broadening of the optical absorption spectrum, in order to distinguish between the different simulated structures. Taken together, we conclude that the hydrated electron likely has a significant number of interior water molecules.

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Section: ■ Controversy Over Hydrated Electron MD Simulationsmentioning

confidence: 99%

“…For example, experiment has shown that the hydrated electron has a radius of gyration of 2.45 Å, 25 respectively (all calculated without the use of Ewald summation, which is known to slightly alter these values 13,19 ). ).…”

Section: ■ Comparing Different Hydrated Electronmentioning

confidence: 99%

To Be or Not to Be in a Cavity: The Hydrated Electron Dilemma

2013

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“…13,29 Specifically, it was shown that the computed trends in the radius and the kinetic energy of the excess electron with cluster size for SB clusters reproduce the tendencies extracted from experiments. 30 Up to now, this is the strongest (and most intriguing) evidence in favor of strong surface-bound excess electronic states in water cluster anions. 13,29 Several recent ab initio quantum chemical studies have also appeared in the literature adding substantially to the debate on both sides.…”

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confidence: 99%

Interior- and surface-bound excess electron states in large water cluster anions

Madarász

Rossky

Túri

2009

The Journal of Chemical Physics

122

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We present the results of mixed quantum/classical simulations on relaxed thermal nanoscale water cluster anions, ( ), with n=200, 500, 1000 and 8000. By using initial equilibration with constraints, we investigate stable/metastable negatively charged water clusters with both surface-bound and interior-bound excess electron states. Characterization of these states is performed in terms of geometrical parameters, energetics, and optical absorption spectroscopy of the clusters. The calculations provide data characterizing these states in the gap between previously published calculations, and experiments, on smaller clusters and the limiting cases of either an excess electron in bulk water, or an excess electron at an infinite water/air interface. The present results are in general agreement with previous simulations and provide a consistent picture of the evolution of the physical properties of water cluster anions with c E-mail: turi@chem.elte.hu, fax: (36)-1-372-2592 madaradam@gmail.com, fax: (36)-1-372-2592 rossky@mail.utexas.edu, fax: (1)-512-471-1624 3 size over the entire size range, including results for vertical detachment energies and absorption spectra that would signify their presence. In particular, the difference in size dependence between surface-bound and interior-bound state absorption spectra is dramatic, while for detachment energies the dependence is qualitatively the same.4 IntroductionThe physics of water cluster anions has remained an important focus of research efforts for more than two decades. The intense scientific interest is largely motivated by the central role of water cluster anions in various important physical processes in atmospheric chemistry, interstellar chemistry, and in electron-initiated processes in aqueous systems. 1 Furthermore, the finite size and the anticipated relative simplicity of water cluster anions, compared to a condensed phase 1 renders them an excellent model for both experimental 2,3,4,5,6,7,8,9,10 and theoretical methods under welldefined conditions. 11,12,13,14 Despite the considerable effort invested, there is still no consensus on the most basic structural properties of water cluster anions. Two distinct localization patterns have been predicted by theory for water cluster anions. In the interior-bound (IB)states, the excess electron localizes in a solvent void surrounded by properly oriented water molecules in clear analogy to the hydrated electron. 11-14, 15,16,17,18,19,20 Theoretical work also suggested that an alternative binding motif may exist with the excess electron being stabilized by the electrostatic reaction field of the cluster dipole, in surface-bound (SB) states, with significant electronic amplitude appearing outside the molecular framework. 11-20Sophisticated experiments on size selected clusters, however, observe at least three characteristic cluster anion classes reflected by three distinctly different trends in the variation of the vertical electron detachment energy with size. 8,9,21 The systematic trends clearly suggest a commonali...

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“…The assignment of the experimentally available data 27,32,33,44,45 to these isomers still generates intense debates. 22,23,32,41,44,76,77 Therefore, it is important to anticipate and examine physical properties that are potentially different in these two states. Here we observe that the two types of cluster isomers relax with significant differences, interior state cavity type clusters relaxing more efficiently than surface cluster…”

Section: Discussionmentioning

confidence: 99%

“…in interior or surface excess electronic states. 21,22,23,32,41,42,43,44,45 Since it is plausible that the main character of the relaxation is different in different localization modes, simulations of electron localization and/or electronic excitation in water cluster anions may provide clues on how to distinguish these isomers experimentally.…”

Section: Introductionmentioning

confidence: 99%

Hydration dynamics in water clusters via quantum molecular dynamics simulations

Túri

2014

The Journal of Chemical Physics

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We have investigated the hydration dynamics in size selected water clusters with n=66, 104, 200, 500 and 1000 water molecules using molecular dynamics simulations. To study the most fundamental aspects of relaxation phenomena in clusters, we choose one of the simplest, still realistic, quantum mechanically treated test solute, an excess electron. The project focuses on the time evolution of the clusters following two processes, electron attachment to neutral equilibrated water clusters and electron detachment from an equilibrated water cluster anion. The relaxation dynamics is significantly different in the two processes, most notably restoring the equilibrium final state is less effective after electron attachment. Nevertheless, in both scenarios only minor cluster size dependence is observed. Significantly different relaxation patterns characterize electron detachment for interior and surface state clusters, interior state clusters relaxing significantly faster. This observation may indicate a potential way to distinguish surface state and interior state water cluster anion isomers experimentally. A Cluster relaxation was also investigated using two different computational models, one preferring cavity type interior states for the excess electron in bulk water, while the other simulating non-cavity structure. While the cavity model predicts appearance of several different hydrated electron isomers in agreement with experiment, the non-cavity model locates only cluster anions with interior excess electron distribution. The present simulations show that surface isomers computed with the cavity predicting potential show similar dynamical behavior to the interior clusters of the non-cavity type model. Relaxation associated with cavity collapse presents, however, unique dynamical signatures.

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Moment analysis of hydrated electron cluster spectra: Surface or internal states?

Cited by 70 publications

References 16 publications

To Be or Not to Be in a Cavity: The Hydrated Electron Dilemma

To Be or Not to Be in a Cavity: The Hydrated Electron Dilemma

Interior- and surface-bound excess electron states in large water cluster anions

Hydration dynamics in water clusters via quantum molecular dynamics simulations

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