Excess electrons in liquid water: First evidence of a prehydrated state with femtosecond lifetime

Migus, A.; Gauduel, Y.; Martin, James L.; Antonetti, A.

doi:10.1103/physrevlett.58.1559

Cited by 500 publications

(425 citation statements)

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“…3 Since liquid water contains no preexisting cavities, the ejected electron must force significant local solvent reorganization, explaining the marked spectral shifts observed following both CTTS excitation of aqueous iodide 4,9 and the multiphoton ionization of neat water. 4,65,68 We propose that the CTTS dynamics of I -in THF are sensibly explained if the single s-like CTTS excited state lies relatively high in the manifold of disjoint states energetically, as suggested at the center of Figure 7. Thus, CTTS excitation of I -in THF leads to rapid nonadiabatic coupling to disjoint states (as depicted by the wiggly green arrow in Figure 7), such that few electrons relax to their ground states near their iodine atom partners.…”

Section: Discussion: Understanding the Roles Of The Solute And Somentioning

confidence: 80%

“…22 In contrast, the tightly packed structure of liquid water does not contain preexisting voids, 62 such that any relocalization 63,64 or other accommodation of a new aqueous electron requires substantial solvent reorganization, as observed both in the aqueous I -CTTS process 1,2,4,24,25 and in the relaxation of excited hydrated electrons. 2,4,[65][66][67][68][69] The presence of preexisting electron traps in liquid THF also can explain the change in Na -CTTS recombination dynamics with excitation energy; excitation at higher energies increases the probability that the initially created CTTS excited state can couple with a disjoint electronic state encompassing other cavities, thus increasing the probability that the excited electrons localize further from the Na 0 core. 22 On the other hand, it is unclear how the s-like CTTS excited state of I -, which in water has been described as an asymmetrically shaped orbital that is larger and more nonspherical than an equilibrated hydrated electron, 58 would be affected by coupling to the low-lying disjoint states that exist as a natural part of the electronic structure of liquid THF.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Charge-Transfer-to-Solvent Dynamics of Iodide in Tetrahydrofuran. 2. Photoinduced Electron Transfer to Counterions in Solution

Bragg

Schwartz

2008

J. Phys. Chem. A

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Although they represent the simplest possible charge-transfer reactions, the charge-transfer-to-solvent (CTTS) dynamics of atomic anions exhibit considerable complexity. For example, the CTTS dynamics of iodide in water are very different from those of sodide (Na -) in tetrahydrofuran (THF), leading to the question of the relative importance of the solvent and solute electronic structures in controlling charge-transfer dynamics. In this work, we address this issue by investigating the CTTS spectroscopy and dynamics of I -in THF, allowing us to make detailed comparisons to the previously studied I -/H 2 O and Na -/THF CTTS systems. Since THF is weakly polar, ion pairing with the counterion can have a substantial impact on the CTTS spectroscopy and dynamics of I -in this solvent. In this study, we have isolated "counterion-free" I -in THF by complexing the Na + counterion with 18-crown-6 ether. Ultrafast pump-probe experiments reveal that THF-solvated electrons (e THF -) appear 380 ( 60 fs following the CTTS excitation of "free" I -in THF. The absorption kinetics are identical at all probe wavelengths, indicating that the ejected electrons appear with no significant dynamic solvation but rather with their equilibrium absorption spectrum. After their initial appearance, ejected electrons do not exhibit any additional dynamics on time scales up to ∼1 ns, indicating that geminate recombination of e THF -with its iodine atom partner does not occur. Competitive electron scavenging measurements demonstrate that the CTTS excited state of I -in THF is quite large and has contact with scavengers that are several nanometers away from the iodide ion. The ejection time and lack of electron solvation observed for I -in THF are similar to what is observed following CTTS excitation of Na -in THF. However, the relatively slow ejection time, the complete lack of dynamic solvation, and the large ejection distance/lack of recombination dynamics are in marked contrast to the CTTS dynamics observed for I -in water, in which fast electron ejection, substantial solvation, and appreciable recombination have been observed. These differences in dynamical behavior can be understood in terms of the presence of preexisting, electropositive cavities in liquid THF that are a natural part of its liquid structure; these cavities provide a mechanism for excited electrons to relocate to places in the liquid that can be nanometers away, explaining the large ejection distance and lack of recombination following the CTTS excitation of I -in THF. We argue that the lack of dynamic solvation observed following CTTS excitation of both I -and Na -in THF is a direct consequence of the fact that little additional relaxation is required once an excited electron nonadiabatically relaxes into one of the preexisting cavities. In contrast, liquid water contains no such cavities, and CTTS excitation of I -in water leads to local electron ejection that involves substantial solvent reorganization.

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Section: Discussion: Understanding the Roles Of The Solute And Somentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Ultrafast Charge-Transfer-to-Solvent Dynamics of Iodide in Tetrahydrofuran. 2. Photoinduced Electron Transfer to Counterions in Solution

Bragg

Schwartz

2008

J. Phys. Chem. A

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“…This time constant, most likely, reflects the excited state lifetime in accord with previous reports. 20,25,31,40,44,47,49 A single-exponential fit to the remainder of the signal yields a decay of ∼110 fs. A rapidly decaying induced transparency and a slowly decaying induced absorption of hydrated electrons excited at 780 nm have been reported before.…”

Section: Methodsmentioning

confidence: 99%

“…The wellseparated spectral line shapes of the intermediate and the fully relaxed electron 38 strongly support a description in terms of three levels, in agreement with the interpretation of earlier experiments and model calculations. 20,58 An alternative route to study the interaction of electrons with water is to perform pump-probe experiments on electrons that have already been equilibrated. 39 It has been argued that the dynamics observed in this type of experiment as, for instance, the relaxation from the excited state, can be fundamentally different, because the electron has substantially changed the local solvent structure in the initial equilibration process.…”

Section: Introductionmentioning

confidence: 99%

“…[13][14][15][16][17][18][19] About a decade ago the first grasp of subpicosecond solvation dynamics was gained by multiphoton ionization of neat water using intense pulses from an amplified CPM laser system. [20][21][22][23][24] A more thorough understanding of the ultrafast dynamics of the electron in water was acquired by subsequent experimental and theoretical investigations. The following picture has emerged from these studies.…”

Section: Introductionmentioning

confidence: 99%

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Wave Packet Dynamics in Ultrafast Spectroscopy of the Hydrated Electron

et al. 1998

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Hydrated-electron dynamics is examined by frequency-resolved pump-probe experiments using pulses of 13 fs centered at 780 nm. A recurrence at ∼40 fs signifies a strong coupling of the electronic transition to underdamped solvent motions. Wave packet dynamics launched by the pump pulse produces an ultrafast red-shift of the electronic transition by approximately 6500 cm -1 . Gross features of the pump-probe experiments are analyzed using a two-level system.

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