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

The effect of adding Na⁺ and Mg²⁺ metal ions on soft X-ray induced photochemistry (SXIP) is investigated. To that aim, the soft X-ray beam of the METROLOGIE beamline at the SOLEIL synchrotron was extracted through air to irradiate solutions circulating in a microfluidic cell. Benzoate was used as a sensitive profluorescent probe for hydroxyl radicals. Hydroxyl radical production yields are relatively constant in the 1.0-1.4 keV energy range, but they are significantly higher in pure benzoate solutions than in solutions supplemented with 1 M sodium or magnesium salts, both below as well as above the ion K-edges. This salt effect is not observed for cesium γ-ray irradiation. Photoelectron spectroscopy, molecular dynamics, and Kinetic Monte Carlo simulations are used to understand the origin of this effect. We conclude that it proceeds by modifying the chemistry occurring within the Auger and photoelectron tracks.