Time-resolved scavenging and recombination dynamics from I:e− caged pairs

Kloepfer, J. A.; Vilchiz, Victor H.; Lenchenkov, Victor; Chen, Xiyi; Bradforth, Stephen E.

doi:10.1063/1.1483292

Cited by 71 publications

(148 citation statements)

References 42 publications

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“…Once the electron is in the lowest solventsupported excited state, the simulations found rapid (Ͻ20 fs) detachment in every run, followed by recombination on longer time scales, in good agreement with Bradforth and co-workers' one-photon experiments. The simulations also predict a unit detachment probability, in agreement with recent reports 12 that have challenged earlier measurements. 13 Although the theoretical results for CTTS discussed above are in good general agreement with experiment, they all have relied on one-electron, mixed quantum/classical MD simulations in which multielectron effects such as exchange are not taken into account.…”

Section: Introductionsupporting

confidence: 88%

The role of electronic symmetry in charge-transfer-to-solvent reactions: Quantum nonadiabatic computer simulation of photoexcited sodium anions

Smallwood

Bosma

Larsen

et al. 2003

The Journal of Chemical Physics

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Since charge-transfer-to-solvent (CTTS) reactions represent the simplest class of solvent-driven electron transfer reactions, there has been considerable interest in understanding the solvent motions responsible for electron ejection. The major question that we explore in this paper is what role the symmetry of the electronic states plays in determining the solvent motions that account for CTTS. To this end, we have performed a series of one-electron mixed quantum/classical nonadiabatic molecular dynamics simulations of the CTTS dynamics of sodide, Na−, which has its ground-state electron in an s orbital and solvent-supported CTTS excited states of p-like symmetry. We compare our simulations to previous theoretical work on the CTTS dynamics of the aqueous halides, in which the ground state has the electron in a p orbital and the CTTS excited state has s-like symmetry. We find that the key motions for Na− relaxation involve translations of solvent molecules into the node of the p-like CTTS excited state. This solvation of the electronic node leads to migration of the excited CTTS electron, leaving one of the p-like lobes pinned to the sodium atom core and the other extended into the solvent; this nodal migration causes a breakdown of linear response. Most importantly, for the nonadiabatic transition out of the CTTS excited state and the subsequent return to equilibrium, we find dramatic differences between the relaxation dynamics of sodide and the halides that result directly from differences in electronic symmetry. Since the ground state of the ejected electron is s-like, detachment from the s-like CTTS excited state of the halides occurs directly, but detachment cannot occur from the p-like CTTS excited state of Na− without a nonadiabatic transition to remove the node. Thus, unlike the halides, CTTS electron detachment from sodide occurs only after relaxation to the ground state and is a relatively rare event. In addition, the fact that the electronic symmetry of sodide is the same as for the hydrated electron enables us to directly study the effect of a stabilizing atomic core on the properties and solvation dynamics of solvent-supported electronic states. All the results are compared to experimental work on Na− CTTS dynamics, and a unified picture for the electronic relaxation for solvent-supported excited states of any symmetry is presented.

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Section: Introductionsupporting

confidence: 88%

The role of electronic symmetry in charge-transfer-to-solvent reactions: Quantum nonadiabatic computer simulation of photoexcited sodium anions

Smallwood

Bosma

Larsen

et al. 2003

The Journal of Chemical Physics

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“…Figure 1b). [1][2][3][4][5] The recombination dynamics following CTTS excitation of I -in THF are also quite different from those of Na -in THF, [10][11][12][13][14][15][16][17][18][19][20][21][22] although the electron ejection time and lack of solvation following ejection are similar for these two solutes (cf. Figure 1d).…”

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

confidence: 99%

“…Figure 1a shows the CTTS absorption spectrum of aqueous I -(blue solid curve), which consists of two broad and featureless bands that peak at 225 and 193 nm; these bands are associated with the two spinorbit states ( 2 P 3/2 and 2 P 1/2 ) of the neutral I atom photoproduct. 41 The dynamics following one-photon CTTS excitation of I -in polar liquids has been investigated extensively by Bradforth and co-workers [1][2][3][4][5]7,8 (as well as by others 9,28 ). A small subset of Bradforth and co-workers' ultrafast spectral measurements associated with the CTTS excitation of aqueous I -are highlighted in Figure 1b; 53 excitation of the I -CTTS band leads to the rapid (<100 fs) appearance of hydrated electrons with a near-unit quantum yield.…”

Section: Introductionmentioning

confidence: 99%

“…A small subset of Bradforth and co-workers' ultrafast spectral measurements associated with the CTTS excitation of aqueous I -are highlighted in Figure 1b; 53 excitation of the I -CTTS band leads to the rapid (<100 fs) appearance of hydrated electrons with a near-unit quantum yield. 3 The newly ejected electrons are formed out of equilibrium and thermalize on a ∼1 ps time scale; 4 the decay at red wavelengths (Figure 1b, red squares) and the corresponding rise at blue wavelengths (Figure 1b, blue circles) indicate a dynamic spectral blue-shift that reflects the equilibration of the ejected hydrated electron (the equilibrated e H 2 O -spectrum is plotted as the red dashed curve in Figure 1a 54,55 ). A significant fraction of the ejected electrons, which reside in I/e solv -contact pairs, subsequently recombine with their I atom parents on an approximately tens-of-picoseconds time scale.…”

Section: Introductionmentioning

confidence: 99%

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The Ultrafast Charge-Transfer-to-Solvent Dynamics of Iodide in Tetrahydrofuran. 1. Exploring the Roles of Solvent and Solute Electronic Structure in Condensed-Phase Charge-Transfer Reactions

Bragg

Schwartz

2007

J. Phys. Chem. B

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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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“…Despite the seeming simplicity of this reaction the mechanism has been long debated [3][4][5]. It is now well established that the reaction is not diffusion limited, but about an order of magnitude slower [1,8,9]. This is due to the large rearrangements of the solvation shells of both H + and e − when forming a neutral H atom [5,10].…”

Section: Introductionmentioning

confidence: 99%

Embedded Cluster Models for Reactivity of the Hydrated Electron

Uhlig

Jungwirth

2013

Zeitschrift Für Physikalische Chemie

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Hydrated Electron / Reactivity / Clusters / Hydronium / Nitrous OxideOur computational study presents embedded cluster models of the hydrated electron focusing on its reactivity with the hydrated proton and the nitrous oxide molecule leading to formation of a hydrogen atom in the former case and a nitrogen molecule plus hydroxyl radical and hydroxide anion in the latter case. We show using ab initio calculations combined with the nudged elastic band method for determining minimum energy paths that carefully chosen cluster models with no more than six water molecules embedded in a polarizable continuum are able to capture the essential features of the reactive processes of the hydrated electron.

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Time-resolved scavenging and recombination dynamics from I:e− caged pairs

Cited by 71 publications

References 42 publications

The role of electronic symmetry in charge-transfer-to-solvent reactions: Quantum nonadiabatic computer simulation of photoexcited sodium anions

The role of electronic symmetry in charge-transfer-to-solvent reactions: Quantum nonadiabatic computer simulation of photoexcited sodium anions

The Ultrafast Charge-Transfer-to-Solvent Dynamics of Iodide in Tetrahydrofuran. 1. Exploring the Roles of Solvent and Solute Electronic Structure in Condensed-Phase Charge-Transfer Reactions

Embedded Cluster Models for Reactivity of the Hydrated Electron

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