Molecular Dynamics Characterization of Dielectron Hydration in Liquid Water with Unique Double Proton Transfers.

Abstract

Radiation chemistry of water and aqueous solutions has always been an interesting scientific issue owing to involving electronic excitations, ionization of solvated species, and formation of radiolytic species and many elementary reactions, but the underlying mechanisms are still poorly understood. Here, we for the first time molecular dynamics characterize the hydration dynamics of two correlated electrons and their triggered unique phenomena in liquid water associated with radiolysis of water using the combined hybrid functional and nonlocal dispersion functional. Hydration of two electrons may experience two distinctly different mechanisms, one forming a spin-paired closed-shell unicaged dielectron hydrate (e22-aq) and the other forming a spin-paired metastable open-shell bicaged hydrated electron pair (e-aq···e-aq) which exhibits intriguing antiferromagnetic spin coupling dynamics (in a range of -40 cm-1 to -500 cm-1). e-aq···e-aq can recombine to e22-aq through a unique solvent fluctuation-controlled gradual-flowing mechanism, and enlarging fluctuation can promote the conversion. Interestingly, we directly observe that e22-aq as the precursor can trigger hydrogen evolution via unique continuous spontaneous double proton transfer to the dielectron with a short-lived H-aq intermediate, but e-aq···e-aq does not directly. This is the first direct observation for the connection between e22-aq and spontaneous hydrogen evolution including participation of H-aq in aqueous solution, bridging relevant experimental phenomena. This work also evidences an unnoticed process, the double proton transfer mediated charge separation, and presents the first detailed analysis regarding the evolution dynamics of e22-aq for the understanding of the radiolysis reactions in aqueous solutions.