How Do Small Water Clusters Bind an Excess Electron?

Hammer, Nathan I.; Shin, Jae–Heon; Headrick, Jeffrey M.; Diken, Eric G.; Roscioli, Joseph R.; Weddle, Gary H.; Johnson, Mark A.

doi:10.1126/science.1102792

Cited by 277 publications

(303 citation statements)

References 36 publications

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“…(12)(13)(14)(15) Already a water dimer is capable of binding an excess electron, (12) however, its character is very different from the bulk hydrated species. In small systems, these are weakly bound and very diffuse dipole-bound electrons, which reside at the exterior of the water cluster.…”

Section: Introductionmentioning

confidence: 99%

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

et al. 2011

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Understanding the properties of hydrated electrons, which were first observed using pulse radiolysis of water in 1962, is crucial because they are key species in many radiation chemistry processes. Although time-resolved spectroscopic studies and molecular simulations have shown that an electron in water (prepared, for example, by water photoionization) relaxes quickly to a localized, cavity-like structure similar to 2.5 angstrom in radius, this picture has recently been questioned. In another experimental approach, negatively charged water clusters of increasing size were studied with photoelectron and IR spectroscopies. Although small clusters can bind an excess electron, their character is very different from bulk hydrated species. As data on electron binding in liquid water have become directly accessible experimentally, the cluster-to-bulk extrapolations have become a topic of lively debate. Quantum electronic structure calculations addressing experimental measurables have, until recently, been largely limited to small clusters; extended systems were approached mainly with pseudopotential calculations combining a classical description of water with a quantum mechanical treatment of the excess electron. In this Account, we discuss our investigations of electrons solvated in water by means of ab initio molecular dynamics simulations. This approach, applied to a model system of a negatively charged cluster of 32 water molecules, allows us to characterize structural, dynamical, and reactive aspects of the hydrated electron using all of the system's valence electrons. We show that under ambient conditions, the electron localizes into a cavity close to the surface of the liquid cluster. This cavity is, however, more flexible and accessible to water molecules than an analogous area around negatively charged ions. The dynamical process of electron attachment to a neutral water cluster is strongly temperature dependent. Under ambient conditions, the electron relaxes in the liquid cluster and becomes indistinguishable from an equilibrated, solvated electron on a picosecond time scale. In contrast, for solid, cryogenic systems, the electron only partially localizes outside of the cluster, being trapped in a metastable, weakly bound "cushion-like" state. Strongly bound states under cryogenic conditions could only be prepared by cooling equilibrated, liquid, negatively charged clusters. These calculations allow us to rationalize how different isomers of electrons in cryogenic clusters can be observed experimentally. Our results also bring into question the direct extrapolation of properties of cryogenic, negatively charged water clusters to those of electrons in the bulk liquid. Ab initio molecular dynamics represents a unique computational tool for investigating the reactivity of the solvated electron in water. As a prototype, the electron proton reaction was followed in the 32-water cluster. In accord with experiment, the molecular mechanism is a proton transfer process that is not diffusion limited, but rat...

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Section: Introductionmentioning

confidence: 99%

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

et al. 2011

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“…This method has proven very useful in recent studies on the microhydration of anions, for example, SO 4 2-and SF 6 -, 24-26 and on water cluster anions. 27,28 Similar to SO 4 2-, NO 3 -is of sufficiently high symmetry to support degenerate vibrational levels. This degeneracy can be lifted upon asymmetric solvation, leading to a splitting of vibrational levels and additional bands in the experimental IR spectra, thereby directly probing the hydration shell environment.…”

Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopy of the Microhydrated Nitrate Ions NO₃⁻(H₂O)₁₋₆

et al. 2009

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We present infrared photodissociation spectra of the microhydrated nitrate ions NO 3 -(H 2 O) 1-6 , measured from 600 to 1800 cm -1 . The assignment of the spectra is aided by comparison with calculated B3LYP/augcc-pVDZ harmonic frequencies, as well as with higher-level calculations. The IR spectra are dominated by the antisymmetric stretching mode of NO 3 -, which is doubly degenerate in the bare ion but splits into its two components for most microhydrated ions studied here due to asymmetric solvation of the nitrate core. However, for NO 3 -(H 2 O) 3 , the spectrum reveals no lifting of this degeneracy, indicating an ion with a highly symmetric solvation shell. The first three water molecules bind in a bidentate fashion to the terminal oxygen atoms of the nitrate ion, keeping the planar symmetry. The onset of extensive water-water hydrogen bonding is observed starting with four water molecules and persists in the larger clusters.

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“…85 It has been shown that electrons can be stabilized by water clusters via dangling hydrogen atoms, i.e., hydrogen atoms that do not participate in the hydrogen bond. [86][87][88] And then this concept was applied to explain the electronic structure at interfaces. )…”

Section: Adsorption Of Methanol On Tio 2 (110)mentioning

confidence: 99%

Surface photochemistry probed by two-photon photoemission spectroscopy

Zhou

Ren

et al. 2012

Energy Environ. Sci.

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Two-photon photoemission (2PPE) has been widely used in the study of electronic structure and dynamics of unoccupied electronic states on different types of surfaces and interfaces. Since 2PPE probes electronically excited states, it should be sensitive to surface excited electronic structure changes that accompany surface chemical reactions. Therefore, this method could potentially be used to study the kinetics and dynamics of surface chemical reactions as well as surface photocatalysis. In this article, we briefly review recent progress made in the study of surface photochemistry and photocatalysis using the time-dependent 2PPE (TD-2PPE) method. A few examples are given to demonstrate the application of this method in probing surface photochemistry and photocatalysis, particularly photocatalysis of methanol on TiO 2 surfaces. Since many problems associated with surface photochemistry and surface photocatalysis are related to energy and environmental issues, the 2PPE technique could have important applications in the study of the fundamental problems in energy and environmental sciences.

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How Do Small Water Clusters Bind an Excess Electron?

Cited by 277 publications

References 36 publications

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

Infrared Spectroscopy of the Microhydrated Nitrate Ions NO₃⁻(H₂O)₁₋₆

Surface photochemistry probed by two-photon photoemission spectroscopy

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How Do Small Water Clusters Bind an Excess Electron?

Cited by 277 publications

References 36 publications

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

Structure, Dynamics, and Reactivity of Hydrated Electrons by Ab Initio Molecular Dynamics

Infrared Spectroscopy of the Microhydrated Nitrate Ions NO3−(H2O)1−6

Surface photochemistry probed by two-photon photoemission spectroscopy

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Infrared Spectroscopy of the Microhydrated Nitrate Ions NO₃⁻(H₂O)₁₋₆