Cesium oxalate under extreme conditions: Theory and experiment*

We have investigated structural changes of cesium oxalate and cesium oxalate monohydrate under extreme conditions. Absorption of sufficiently energetic X-ray photons by a molecular system results in a cascade of ultrafast electronic relaxation processes which leads to a distortion and dissociation of its molecular structure. It is found that there is a distinct difference between cesium oxalate and cesium oxalate monohydrate when exposed to x-ray and high pressure conditions. X-ray induced degradation of powdered cesium oxalate monohydrate occurred under high pressure, leading to the formation of a new compound while no dramatic change was observed in case of cesium oxalate when subjected to the same extreme conditions. Our combined theory and experimental study suggests that the presence of water molecules in initially solid-state systems is important for such X-ray induced photochemistry when combined with applied high pressure.