Wet electrons

Wet electrons in chemistry and physics, which occur on the surface of metal oxides, are a transition state for electrons between the solid and liquid states of matter. Wet electrons are attracted to positively charged hydroxide ions which form on oxide surfaces in the presence of atmospheric moisture. These electrons in turn affect the interaction of other materials with the oxide.

Hydrogen atoms on water or hydroxide (OH) can be involved in hydrogen bonds or be dangling. Wet electrons are primarily stabilized by the dangling atoms on OH, which is more acidic than water, but the dangling atoms on water also contribute to the stabilization. The process is akin to following the lowest elevation path between valleys with a mountain between them. The minimum energy necessary to change an electron from the solid to the liquid state corresponds to going through the wet electron state. Wet electrons are a transition state (saddle point) between electrons in the liquid and solid states.

Formation and Localization
Wet electrons are produced when high-energy radiation, such as gamma rays, X-rays, or energetic particles, ionizes water molecules. This ionization results in the liberation of electrons, which, instead of remaining free, can become transiently localized due to interactions with the surrounding water molecules. This localization occurs as the electron induces a polarization in nearby water molecules, creating a potential well that temporarily stabilizes the electron in a state known as the wet electron.

Physical Properties
Wet electrons are characterized by their intermediate energy state, which is above the ground state energy of water but below the energy level of a free electron. This state is highly reactive due to its excess energy, making wet electrons potent reducing agents capable of engaging in various chemical reactions. The lifetime of a wet electron is typically very short, on the order of picoseconds, depending on the specific environmental conditions and the presence of other reactive species.

Detection and Theoretical Insights
Advanced experimental techniques such as pulse radiolysis and time-resolved spectroscopy have been pivotal in detecting and studying the behavior of wet electrons. These methods allow scientists to observe the transient absorption features of wet electrons and monitor their behavior in real-time.

Theoretical studies, particularly those using hybrid functional molecular dynamics simulations, provide deeper insights into the dynamics and energetics of wet electrons. These studies suggest that wet electrons frequently transition between a quasi-free state in the conduction band and a localized state. This transition is accompanied by significant disruptions in the hydrogen-bond network of the surrounding water molecules, which facilitate the localization and stabilization of the electron.

Energetics and Structural Dynamics
The energy associated with the localized state of wet electrons is typically a few tenths of an eV below the conduction band minimum. This energy state reflects the complex interplay between the electron and the polar environment of water. Theoretical investigations indicate that the localization of a wet electron involves a severe distortion of the local hydrogen-bond network, often resulting in the formation of a transient cavity within the liquid structure. This cavity is formed by the rearrangement and orientation of water molecules around the trapped electron, influenced by their dipolar nature.