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

In the radiation chemistry of water, two hydrated electrons () can react to form H and OH. Experiments and simulations suggest that this reaction occurs through a mechanism involving colocalization of two 's into the same solvent cavity, forming a hydrated dielectron intermediate, with aqueous hydride (H) as a subintermediate. However, there has been no direct experimental observation of either or H. Here, we present TD-DFT-based predictions for the absorption spectrum of open-shell-singlet and triplet pairs, , and H. We find that relative to , triplet and open-shell singlet electron pairs show spectral shifts to the blue and red, respectively. Additionally, we find that 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 and H.