Abstract
In the radiation chemistry of water, two hydrated electrons (e(hyd)(-)) can react to form H(2) 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 ((ehyd)22-) intermediate, with aqueous hydride (H(-)) as a subintermediate. However, there has been no direct experimental observation of either (ehyd)22- or H(-). Here, we present TD-DFT-based predictions for the absorption spectrum of open-shell-singlet and triplet e(hyd)(-) pairs, (ehyd)22-, 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 (ehyd)22- 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 (ehyd)22- and H(-).