Exploring the Unusual Reactivity of the Hydrated Electron with CO<sub>2</sub>

Neupane, Pauf; Bartels, David M.; Thompson, Ward H.

doi:10.1021/acs.jpcb.3c06935

J. Phys. Chem. B

2024

DOI: 10.1021/acs.jpcb.3c06935

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Exploring the Unusual Reactivity of the Hydrated Electron with CO₂

Pauf Neupane,

David M. Bartels,

Ward H. Thompson

Abstract: Many questions remain about the reactions of the hydrated electron despite decades of study. Of particular note is that they do not appear to follow the Marcus theory of electron transfer reactions, a feature that is yet to be explained. To investigate these issues, we used ab initio molecular dynamics (AIMD) simulations to investigate one of the better studied reactions, the hydrated electron reduction of CO 2 . The rate constant for the hydrated electron−CO 2 reaction complex to react to form CO 2 − is for t… Show more

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Cited by 3 publications

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Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor

Borrelli,

Liu,

Schwartz

2024

J. Chem. Theory Comput.

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Modeling the various properties of liquid water, particularly its reactivity, has been a longstanding challenge for simulation methods. Recently, ab initio simulations based on density functional theory (DFT) have come to the fore as tenable methods for calculating the properties and reactivity of water, with varying degrees of success for different exchange-correlation functionals. In particular, hybrid-GGA and meta-GGA functionals have been shown to reproduce many of the structural, dynamical, and energetic properties of water to a high degree of accuracy relative to their computational cost. Here, we show that the dual descriptor (DD) measure of nucleophilicity and electrophilicity, which is sometimes used to elucidate organic chemistry reaction mechanisms, can also be used to characterize the reactivity of DFTsimulated liquid water. The DD is especially apt for understanding the reactivity of excess electrons with water as its calculation explicitly involves adding and removing an excess electron from a reference system. We use the DD to explore the reactivity of water simulated using three different DFT functionals: the LDA functional (LDA), a hybrid-GGA functional (PBE0), and a hybrid meta-GGA functional (SCAN0). Using the DD, we show that the SCAN0 functional with the standard 25% Hartree−Fock exchange produces simulated liquid water with many regions that are far more reactive than either PBE0 or LDA. To understand the implications of these highly reactive regions, we then add a strong nucleophile in the form of an excess electron and find that although PBE0 and LDA predict stable hydrated electrons, the excess electron reacts nearly instantaneously with SCAN0 water via proton abstraction to form a hydrogen atom and hydroxide ion. We show that the DD provides the ability to not only predict whether or not liquid water will react with a hydrated electron but also which particular waters will be involved solely from analyzing pure water configurations generated with each functional. We rationalize this result in terms of the known trap-seeking behavior of injected hydrated electrons, which are able to find the most electronegative region in bulk water. These results highlight the utility of the dual descriptor as a fast and interpretable method for investigating condensed-phase reactivity with excess electrons.

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Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor

Borrelli,

Liu,

Schwartz

2024

J. Chem. Theory Comput.

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Roles of H-Bonding and Hydride Solvation in the Reaction of Hydrated (Di)electrons with Water to Create H₂ and OH^–

Borrelli,

Guardado Sandoval,

Mei

et al. 2024

J. Chem. Theory Comput.

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Even though single hydrated electrons (e hyd –’s) are stable in liquid water, two hydrated electrons can bimolecularly react with water to create H2 and hydroxide: e hyd – + e hyd – + 2H2O → H2 + 2OH–. The rate of this reaction has an unusual temperature and isotope dependence as well as no dependence on ionic strength, which suggests that cosolvation of two electrons as a single hydrated dielectron (e 2,hyd 2–) might be an important intermediate in the mechanism of this reaction. Here, we present an ab initio density functional theory study of this reaction to better understand the potential properties, reactivity, and experimental accessibility of hydrated dielectrons. Our simulations create hydrated dielectrons by first simulating single e hyd –’s and then injecting a second electron, providing a well-defined time zero for e 2,hyd 2– formation and offering insight into a potential experimental route to creating dielectrons and optically inducing the reaction. We find that e 2,hyd 2– immediately forms in every member of our ensemble of trajectories, allowing us to study the molecular mechanism of H2 and OH– formation. The subsequent reaction involves separate proton transfer steps with a generally well-defined hydride subintermediate. The time scales for both proton transfer steps are quite broad, with the first proton transfer step spanning times over a few ps, while the second proton transfer step varies over ∼150 fs. We find that the first proton transfer rate is dictated by whether or not the reacting water is part of an H-bond chain that allows the newly created OH– to rapidly move by Grotthuss-type proton hopping to minimize electrostatic repulsion with H–. The second proton transfer step depends significantly on the degree of solvation of H–, leading to a wide range of reactive geometries where the two waters involved can lie either across the dielectron cavity or more adjacent to each other. This also allows the two proton transfer events to take place either effectively concertedly or sequentially, explaining differing views that have been presented in the literature.

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How to Probe Hydrated Dielectrons Experimentally: Ab Initio Simulations of the Absorption Spectra of Aqueous Dielectrons, Electron Pairs, and Hydride

Mei,

Borrelli,

Guardado Sandoval

et al. 2024

J. Phys. Chem. Lett.

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In the radiation chemistry of water, two hydrated electrons (e hyd −) can react to form H2 and OH–. Experiments and simulations suggest that this reaction occurs through a mechanism involving colocalization of two e hyd −’s into the same solvent cavity, forming a hydrated dielectron false( ( e h y d ) 2 2 − false) intermediate, with aqueous hydride (H–) as a subintermediate. However, there has been no direct experimental observation of either false( e normalh normaly normald false) 2 2 − or H–. Here, we present TD-DFT-based predictions for the absorption spectrum of open-shell-singlet and triplet e hyd ‑ pairs, false( e normalh normaly normald false) 2 2 − , and H–. We find that relative to e hyd −, triplet and open-shell singlet electron pairs show spectral shifts to the blue and red, respectively. Additionally, we find that false( e normalh normaly normald false) 2 2 − absorbs even further to the red, and that H– has a charge-transfer-to-solvent-like transition at wavelengths several eV to the blue, providing a direct experimental handle with which to probe these species. We propose a three-pulse transient absorption experiment that should allow detection of false( e normalh normaly normald false) 2 2 − and H–.

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Exploring the Unusual Reactivity of the Hydrated Electron with CO₂

Cited by 3 publications

References 52 publications

Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor

Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor

Roles of H-Bonding and Hydride Solvation in the Reaction of Hydrated (Di)electrons with Water to Create H₂ and OH^–

How to Probe Hydrated Dielectrons Experimentally: Ab Initio Simulations of the Absorption Spectra of Aqueous Dielectrons, Electron Pairs, and Hydride

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Exploring the Unusual Reactivity of the Hydrated Electron with CO2

Cited by 3 publications

References 52 publications

Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor

Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor

Roles of H-Bonding and Hydride Solvation in the Reaction of Hydrated (Di)electrons with Water to Create H2 and OH–

How to Probe Hydrated Dielectrons Experimentally: Ab Initio Simulations of the Absorption Spectra of Aqueous Dielectrons, Electron Pairs, and Hydride

Contact Info

Product

Resources

About

Exploring the Unusual Reactivity of the Hydrated Electron with CO₂

Roles of H-Bonding and Hydride Solvation in the Reaction of Hydrated (Di)electrons with Water to Create H₂ and OH^–