Vibrational spectroscopy of hydrated electron clusters(H2O)15–50− via infrared multiple photon dissociation

Asmis, Knut R.; Santambrogio, Gabriele; Zhou, Jia; Garand, Etienne; Headrick, Jeffrey M.; Goebbert, Daniel J.; Johnson, Mark A.; Neumark, Daniel M.

doi:10.1063/1.2741508

Cited by 78 publications

(94 citation statements)

References 37 publications

(29 reference statements)

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“…The set of vibrational spectra has been recently extended with the infrared free electron laser FELIX to clusters as large as n ) 50. 29 While IR spectra up to n ) 24 reproduced the previous findings, larger clusters showed continuous broadening of the AA feature until it merged with the main bending mode at 1640 cm -1 around n ) 50, raising the question about a potential structural transition in this size range. The nature of the electron binding motif in larger water cluster anions has also been the focus of several recent theoretical investigations.…”

Section: Water Cluster Anionssupporting

confidence: 65%

Dynamics of Electron Solvation in Molecular Clusters

Ehrler

Neumark

2009

Acc. Chem. Res.

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S olvated electrons, and hydrated electrons in particular, are important species in condensed phase chemistry, physics, and biology. Many studies have examined the formation mechanism, reactivity, spectroscopy, and dynamics of electrons in aqueous solution and other solvents, leading to a fundamental understanding of the electron-solvent interaction. However, key aspects of solvated electrons remain controversial, and the interaction between hydrated electrons and water is of central interest. For example, although researchers generally accept that hydrated electrons, e aq -, occupy solvent cavities, another picture suggests that the electron resides in a diffuse orbital localized on a H 3 O radical. In addition, researchers have proposed two physically distinct models for the relaxation mechanism when the electron is excited. These models, formulated to interpret condensed phase experiments, have markedly different time scales for the internal conversion from the excited p state to the ground s state.Studies of negatively charged clusters, such as (H 2 O) n -and I -(H 2 O) n , offer a complementary perspective for studying aqueous electron solvation. In this Account, we use time-resolved photoelectron spectroscopy (TRPES), a femtosecond pump-probe technique in which mass-selected anions are electronically excited and then photodetached at a series of delay times, to focus on time-resolved dynamics in these and similar species. In (H 2 O) n -, TRPES gives evidence for ultrafast internal conversion in clusters up to n ) 100. Extrapolation of these results yields a p-state lifetime of 50 fs in the bulk limit. This is in good agreement with the nonadiabatic solvation model, one of the models proposed for relaxation of e aq -. Similarly, experiments on (MeOH) n -up to n ) 450 give an extrapolated p-state lifetime of 150 fs.TRPES investigations of I -(H 2 O) n and I -(CH 3 CN) n probe a different aspect of electron solvation dynamics. In these experiments, an ultraviolet pump pulse excites the cluster analog of the charge-transfer-to-solvent (CTTS) band, ejecting an electron from the iodide into the solvent network. The probe pulse then monitors the solvent response to this excess electron, specifically its stabilization via solvent rearrangement. In I -(H 2 O) n , the iodide sits outside the solvent network, as does the excess electron initially formed by CTTS excitation. However, the iodide in I -(CH 3 CN) n is internally solvated, and both experimental and theoretical evidence indicate that electrons in (CH 3 CN) n -are internally solvated. Hence, these experiments reflect the complex dynamics that ensue when the electron is photodetached within a highly confined solvent cavity.

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Section: Water Cluster Anionssupporting

confidence: 65%

Dynamics of Electron Solvation in Molecular Clusters

Ehrler

Neumark

2009

Acc. Chem. Res.

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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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“…Results from femtosecond resolved photoelectron imaging of the electron dynamics in (H 2 O) n Ϫ (19,20) suggest that an interior electronic state was probed (19). Recent infrared spectroscopy data of such clusters provide important insights into electron-water interactions, but do not resolve the electron location debate (27).…”

Section: ؉mentioning

confidence: 99%

Nanocalorimetry in mass spectrometry: A route to understanding ion and electron solvation

Donald

Leib

O’Brien

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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A gaseous nanocalorimetry approach is used to investigate effects of hydration and ion identity on the energy resulting from ionelectron recombination. Capture of a thermally generated electron by a hydrated multivalent ion results in either loss of a H atom accompanied by water loss or exclusively loss of water. The energy resulting from electron capture by the precursor is obtained from the extent of water loss. Results for large-size-selected clusters of Co(NH 3)6(H2O)n 3؉ and Cu(H2O) n 2؉ indicate that the ion in the cluster is reduced on electron capture. The trend in the data for Co(NH 3)6(H2O)n 3؉ over the largest sizes (n > 50) can be fit to that predicted by the Born solvation model. This agreement indicates that the decrease in water loss for these larger clusters is predominantly due to ion solvation that can be accounted for by using a model with bulk properties. In contrast, results for Ca(H 2O)n 2؉indicate that an ion-electron pair is formed when clusters with more than Ϸ20 water molecules are reduced. For clusters with n ‫؍‬ Ϸ20 -47, these results suggest that the electron is located near the surface, but a structural transition to a more highly solvated electron is indicated for n ‫؍‬ 47-62 by the constant recombination energy. These results suggest that an estimate of the adiabatic electron affinity of water could be obtained from measurements of even larger clusters in which an electron is fully solvated.clusters ͉ ECD ͉ recombination ͉ hydration I on-solvent interactions are fundamental to many important phenomena in chemistry and biology, including ion transport across cell walls, salt-bridge formation, surface tension, and protein stability, yet many aspects of such interactions are still not well understood. Mass spectrometry is an important tool for probing ion-solvent interactions and has been widely used to obtain valuable thermochemical information. The ability to form gaseous hydrated clusters of many di-(1) and trivalent (2) ions has greatly expanded the capabilities of mass spectrometry to investigate important ion solvation problems. Structural information of hydrated ions has been obtained from a variety of thermochemical methods (3-5) and spectroscopy (6-9). From these studies, information about how water molecules organize around ions and how water can affect the structures of ions themselves can be obtained (8,9).Investigating the most fundamental aqueous ion, the hydrated electron, is challenging because of its powerful reducing nature (E 1/2 0 ϭ Ϫ2.87 V) (10) and high reactivity. Solvated electrons have been observed in many different solvents (11) and are important intermediates in radiation chemistry, electron transfer processes, and many biological processes, including those that can lead to irreversible cell damage. The structure of the hydrated electron has been investigated by several methods, including electron spin resonance (12) and Raman spectroscopy (13), but many details about the structure of the solvent cavity that traps the electron remain elusive.Information ab...

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Vibrational spectroscopy of hydrated electron clusters(H2O)15–50− via infrared multiple photon dissociation

Cited by 78 publications

References 37 publications

Dynamics of Electron Solvation in Molecular Clusters

Dynamics of Electron Solvation in Molecular Clusters

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

Nanocalorimetry in mass spectrometry: A route to understanding ion and electron solvation

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Vibrational spectroscopy of hydrated electron clusters(H2O)15–50− via infrared multiple photon dissociation

Cited by 78 publications

References 37 publications

Dynamics of Electron Solvation in Molecular Clusters

Dynamics of Electron Solvation in Molecular Clusters

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

Nanocalorimetry in mass spectrometry: A route to understanding ion and electron solvation

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