Intense Reactivity in Sulfur-Hydrogen Mixtures at High Pressure under X-ray Irradiation

Superconductivity near room-temperature in the sulfur-hydrogen system arises from a sequence of reactions at high pressures, with x-ray diffraction experiments playing a central role in understanding these chemical-structural transformations and the corresponding S:H stoichiometry. Here we document x-ray irradiation acting as both a probe and as a driver of chemical reaction in this dense hydride system. We observe reaction between molecular hydrogen
(H2) and elemental sulfur (S8) under high pressure, induced directly by x-ray illumination, at photon energies of 12 keV using a free electron laser. The rapid synthesis of hydrogen sulphide (H2S) at 0.3 GPa was confirmed by optical observations, spectroscopic measurements, and micro-structural changes detected by x-ray diffraction. These results document x-ray induced chemical synthesis of superconductor-forming dense hydrides, revealing an alternative production strategy and confirming the disruptive nature of x-ray exposure in studies on high-pressure hydrogen chalcogenides, from water to high-temperature superconductors.