The Fate of Secondary Electrons in Water upon High-Energy Electron Impact: Changes in the Presence of Nanobubbles

Electrons localized by water molecules are known as hydrated electrons. The composition of the aqueous environment determines their state and behavior. In this experimental and theoretical work, hydrated electrons were formed in aqueous solutions upon high-energy electron impact, and the dependence of their characteristics on the presence of nanobubbles generated during vibrational treatment was investigated. To explain the results, quantum chemical simulations were carried out, and diverse possible kinetic schemes were considered. Absorbance of deionized water and NaCl aqueous solution was measured at a wavelength of 600 nm, which falls in the range typical of hydrated electrons. The principal differences in the spectral responses of the samples were discovered depending on whether they were preliminarily subjected to repeated vigorous shaking or not. Vigorous shaking caused a noticeable increase in both the integral and maximum absorbance, and the absorbance decay was significantly slower. The effects observed in the vibrationally treated aqueous samples were found to be explained only in the framework of a kinetic scheme that assumes the repeated solvation of electrons, which are transferred from a localized to a delocalized (free) state upon the energy absorption. This repeated solvation is possible only when the secondary electrons are localized on the inner surfaces of the boundary hydration shells of nanobubbles, which are formed in the process of shaking. Thus, nanobubbles substantially change the apparent gross lifetime and properties of hydrated electrons, and these changes, in turn, can indicate the presence of nanobubbles in water and aqueous solutions.