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This study employs ab initio molecular dynamics simulations to explore how alkali metal cations, specifically Li$^+$ and Cs$^+$, influence the structure and reactivity of hydrated dielectrons. The findings reveal that while the overall solvation structure remains consistent, the presence of cations increases the dielectron gyration radius by approximately 10% and leads to unique cation-dielectron arrangements. Additionally, the research identifies significant elongation of first-shell O-H bonds towards the dielectron, providing insights into the vibrational red-shifts observed in resonance Raman measurements and suggesting that metal cations may inhibit dielectron reactivity over short timescales.
The presence of alkali metal cations not only alters the structural dynamics of hydrated dielectrons but also suppresses their reactivity, challenging previous assumptions about their behavior in solution.
Hydrated electrons of opposite spins pair to form dielectrons at sufficiently high concentrations that can be achieved by dissolution of alkali metals in water. While experimental investigations of these systems are challenging due to their vigorous, even explosive, reactivity, simulations open the possibility to characterize the structure and reactivity of hydrated dielectrons and the effects of alkali cations thereon. Here, we present ab initio molecular dynamics simulations of a hydrated dielectron without or with explicit Li$^+$ or Cs$^+$ counterions. While the overall solvation structure is preserved in all these systems, the presence of cations has a distinct effect of increasing the dielectron gyration radius by about 10% and forming cation-specific cation-dielectron arrangements. Moreover, analysis of water bond lengths reveals in all studied systems a substantial elongation of first-shell O-H bonds oriented toward the dielectron, providing a structural explanation for vibrational red-shifts observed in resonance Raman measurements. Finally, at the 10 ps simulation timescale, rare reactive events were observed, albeit only for the system without metal cations, where hydride intermediates stable on picosecond timescales were identified. These observations also suggest that on the investigated timescales, metal cations may suppress hydrated dielectron reactivity.
