The Hydrated Electron

Abstract

Existence of a hydrated electron as a byproduct of water radiolysis was established more than 50 years ago, yet this species continues to attract significant attention due to its role in radiation chemistry, including DNA damage, and because questions persist regarding its detailed structure. This work provides an overview of what is known in regards to the structure and spectroscopy of the hydrated electron, both in liquid water and in clusters [Formula: see text], the latter of which provide model systems for how water networks accommodate an excess electron. In clusters, the existence of both surface-bound and internally bound states of the excess electron has elicited much debate, whereas in bulk water there are questions regarding how best to understand the structure of the excess electron's spin density. The energetics of the equilibrium species e(aq) and its excited states, in bulk water and at the air/water interface, are also addressed.

Dynamics of the Bulk Hydrated Electron from Many‐Body Wave‐Function Theory

“…Importantly, we observe the regions of negative spin density, giving rise to a negative isotropic hyperfine coupling and essential for explaining EPR spectra . Negative spin density regions have not been reported in the bulk DFT‐based QM/MM studies, although they are predicted by most simulations . As it can be seen in Figure , our study based on MP2 correlated wave function MD confirms negative spin density regions in the condensed phase.…”

Genuine binding energy of the hydrated electron

“…Substantial progress has been made in recent years regarding its structural and electronic properties ( 5 – 21 ) and the excited-state relaxation dynamics over a broad time window, ranging from femtoseconds to beyond picoseconds ( 9 , 10 , 13 , 22 – 32 ). The most controversial issues concern the ground-state structure (cavity-forming versus non–cavity-forming), the relaxation mechanisms from electronically excited states (adiabatic versus nonadiabatic), the existence of a long-lived surface electron, accurate values for electron binding energies (eBE), and the influence of electron scattering.…”

Picture of the wet electron: a localized transient state in liquid water

“…Besides the fundamental interest in understanding the response of liquid water to an excess charge, this species is relevant to numerous applications, including its role, e.g., as a reducing agent in synthetic chemistry or in inducing mutagenic lesions in DNA. 17,18 It is now well-established that, under thermodynamic equilibrium conditions, the hydrated electron is accommodated in a quasi-spherical electrophilic cavity with a radius of $1.8Å formed upon the re-arrangement of about ve water molecules. 8,[19][20][21] It occupies a s-like ground state within the band gap of the solvent, 17,22 from which it can be excited to p-like states through optical transitions of $1.7 eV.…”