Deciphering the reaction between a hydrated electron and a hydronium ion at elevated temperatures

Understanding how electrons interact with water molecules at high temperatures is a complex challenge in chemical physics. While the behavior of hydrated electrons in water is well-studied at ambient conditions, less is known about their reactivity under extreme conditions. Prior research has shown that hydrated electrons can form transient species with hydronium ions, but the effects of temperature and ionic strength remain unclear. This uncertainty drives the need for experiments that can track these reactions in real time. The role of deuterium in modifying reaction pathways is also not fully understood. Existing models often fail to account for temperature-dependent changes in ionic interactions. The formation of transient electron-hydronium pairs has been observed, but their stability at high temperatures is unexplored. The influence of D3O(+) concentration on electron absorption spectra is a recent discovery. This gap motivates the use of advanced pulse radiolysis techniques to explore these phenomena.

This study aims to investigate the reaction between hydrated electrons and hydronium ions in acidic water at elevated temperatures. The primary goal is to determine how temperature and ionic strength affect the formation and decay of transient species. The researchers focus on D2O solutions to better understand deuterium's role in electron-hydronium interactions. By measuring absorption spectra, they seek to identify the conditions under which transient electron-hydronium pairs form. The study also tests whether the presolvated electron remains stable at high temperatures. The temperature range of 200–350 °C is chosen to observe both low- and high-temperature effects. The researchers aim to clarify how D3O(+) concentration influences electron absorption. The ultimate goal is to refine kinetic models to better predict reaction rates under these conditions.

The researchers used picosecond pulse radiolysis to study electron-hydronium interactions in acidic D2O solutions. The experiments were conducted at temperatures up to 350 °C using perchloric acid solutions. Absorption spectra were recorded to track the formation of transient species. The study focused on D3O(+) concentrations up to 0.1 mol L(-1). The temperature dependence of the solvated electron absorption band was analyzed. The researchers applied a kinetic model to fit the observed decay rates. The model included parameters for ionic strength and temperature dependence. The experiments were repeated under varying conditions to assess reproducibility.

The study found that D3O(+) significantly affects the red shift of the solvated electron absorption band in D2O. Transient electron-hydronium pairs formed at 200–250 °C when D3O(+) concentration exceeded 0.05 mol L(-1). These pairs were no longer detectable at 300 and 350 °C, where reaction rates became diffusion-controlled. The presolvated electron remained stable in D2O up to 250 °C in 0.1 mol L(-1) D3O(+) solutions. The decay rates of the electron species were strongly temperature-dependent. Ionic strength also played a key role in determining reaction rates. The proposed model successfully fit the data by accounting for both temperature and ionic strength. The model's parameter A showed a clear temperature dependence.

The authors conclude that D3O(+) concentration and temperature strongly influence the behavior of solvated electrons in acidic D2O. Transient electron-hydronium pairs form at intermediate temperatures but not at higher ones. The model incorporating ionic strength and temperature dependence provides a good fit to the data. The study suggests that electron-hydronium interactions are sensitive to both thermal and ionic conditions. The results support the idea that D3O(+) modifies electron absorption spectra in a temperature-dependent manner. The absence of transient pairs at 300–350 °C indicates a shift to diffusion-controlled kinetics. The model's success implies that temperature and ionic strength are key factors in electron-hydronium reactions. These findings may help refine kinetic models for high-temperature aqueous systems.