Temperature Dependent Properties of the Aqueous Electron**

Abstract

The temperature‐dependent properties of the aqueous electron have been extensively studied using mixed quantum‐classical simulations in a wide range of thermodynamic conditions based on one‐electron pseudopotentials. While the cavity model appears to explain most of the physical properties of the aqueous electron, only a non‐cavity model has so far been successful in accounting for the temperature dependence of the absorption spectrum. Here, we present an accurate and efficient description of the aqueous electron under various thermodynamic conditions by combining hybrid functional‐based molecular dynamics, machine learning techniques, and multiple time‐step methods. Our advanced simulations accurately describe the temperature dependence of the absorption maximum in the presence of cavity formation. Specifically, our work reveals that the red shift of the absorption maximum results from an increasing gyration radius with temperature, rather than from global density variations as previously suggested.

Investigation of the Failure of Marcus Theory for Hydrated Electron Reactions

“…Regardless, we find that, starting from the most strongly bound configuration (the largest VDE ), R g initially increases linearly with decreasing VDE . A decrease in R g with increasing VDE has been observed in several previous studies. ,, However, near the equilibrium VDE value (where Δ A is a minimum), the rate of change of R g with the VDE increases dramatically. As VDE decreases below 5 eV, the hydrated electron grows more rapidly in size.…”

“…A decrease in R g with increasing VDE has been observed in several previous studies. 18,20,55 However, near the equilibrium VDE value (where ΔA is a minimum), the rate of change of R g with the VDE increases dramatically. As VDE decreases below 5 eV, the hydrated electron grows more rapidly in size.…”

“…Specifically, Larsen et al proposed an unusual noncavity model, in contrast to the traditional viewpoint of the hydrated electron as occupying a cavity within liquid water. However, the cavity picture has emerged from this decade-long kerfuffle as the proper description, − as has been observed in electronic structure-based descriptions. − Thus, in the present work we study the hydrated electron behavior using the Turi–Borgis (TB) pseudopotential, which produces a cavity-residing electron. The extensive statistical sampling presented in this work would be challenging within a density functional theory description of the solvated electron.…”

“…This model is not consistent with experiment, but it is an important check on the generality of our conclusions because it represents a qualitatively different description, and the most fluxional model available, for the hydrated electron. In particular, electronic structure-based simulations indicate behavior of the hydrated electron that is intermediate between the TB and the LGS models. − For example, quantum mechanics/molecular mechanics simulations by Jungwirth and co-workers found that the hydrated electron is more delocalized over the first and second solvation shells than predicted by the TB model but still exhibits a distinct cavity structure unlike that given by the LGS description. , …”

“…As noted above, this provides an important comparison as its description of the electron differs most strongly from that of the TB model. In particular, electronic structure-based descriptions reported in the literature give hydrated electron properties and behavior intermediate between the TB and LGS pseudopotentials. − The LGS model results are shown in Figure . Interestingly, the free energy profile as a function of VDE is not harmonic, in contrast to the TB pseudopotential results.…”