Solution Properties Can Strongly Affect X-ray Induced Photochemistry/Radiation Damages through Photoelectron Tracks

Area of Science:

• Physical Chemistry
• Radiation Chemistry
• Materials Science

Background:

• Soft X-ray induced photochemistry (SXIP) is a developing field with applications in materials science and radiation biology.
• Understanding the influence of solution composition on SXIP is crucial for controlling photochemical reactions.
• Hydroxyl radicals are key reactive species produced in water radiolysis and photochemistry.

Purpose of the Study:

• To investigate the impact of sodium (Na+) and magnesium (Mg2+) ions on hydroxyl radical production during SXIP.
• To elucidate the mechanism behind the observed salt effect in SXIP.
• To compare SXIP salt effects with those observed in gamma-ray irradiation.

Main Methods:

• Irradiation of benzoate solutions with soft X-rays (1.0-1.4 keV) from the METROLOGIE beamline at SOLEIL.
• Utilized benzoate as a profluorescent probe to quantify hydroxyl radical yields.
• Employed photoelectron spectroscopy, molecular dynamics, and Kinetic Monte Carlo simulations for mechanistic studies.

Main Results:

• Hydroxyl radical production yields were found to be significantly lower in 1 M sodium or magnesium salt solutions compared to pure benzoate solutions.
• This salt effect was observed both below and above the K-edges of the added ions.
• The observed salt effect in SXIP was not replicated when using cesium gamma-ray irradiation.

Conclusions:

• The presence of Na+ and Mg2+ ions modifies the chemistry within the Auger and photoelectron tracks generated during SXIP.
• This modification leads to a suppression of hydroxyl radical formation.
• The findings highlight the distinct nature of SXIP compared to gamma-ray radiolysis concerning ionic effects.