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

• Published in: The journal of physical chemistry letters Vol. 15; no. 38; pp. 9557 - 9565
• Main Authors: Mei, Kenneth J., Borrelli, William R., Guardado Sandoval, José L., Schwartz, Benjamin J.
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 12.09.2024
• Subjects: Absorption spectroscopy; Anions; Cavities; Chemical calculations; Letter; Physical Insights into Light Interacting with Matter; Quantum mechanics
• ISSN: 1948-7185; 1948-7185
• DOI: 10.1021/acs.jpclett.4c02404

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 ( ( e h y d ) 2 2 − ) intermediate, with aqueous hydride (H–) as a subintermediate. However, there has been no direct experimental observation of either ( e h y d ) 2 2 − or H–. Here, we present TD-DFT-based predictions for the absorption spectrum of open-shell-singlet and triplet e hyd ‑ pairs, ( e h y d ) 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 ( e h y d ) 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 ( e h y d ) 2 2 − and H–.