The HighEneCh ANR project aims to initiate and organize collaborative work between specialists of electron spectroscopy and instrumentation at large-scale facilities (SOLEIL, UPMC – LCP-MR), radiation chemistry (CEA - NIMBE), microfluidic systems (CEA – NIMBE) and ab initio molecular dynamics simulations (UPMC - IMPMC), with the goal of extending the boundaries of fundamental knowledge of the different mechanisms involved in the chemistry in aqueous environments triggered by high-energy photons. Using complementary approaches, the HighEneCh project consortium wants, over the 48 months’ duration of the project, to achieve a global view of the radiolysis of pure water and of water/biomolecule mixtures irradiated with soft X-ray and hard X-ray synchrotron light, with a special focus on the chemical effects of core ionizations. Irradiation with high-energy photons (x-ray) produces charged and neutral species which can both influence the production of the damage caused by the radiation via direct and indirect processes, respectively. The original approach of our consortium is to combine state-of-the-art quantification methods for the detection of radical species with photo/Auger electron spectroscopy on liquids, supported by ab initio molecular dynamics simulations to elucidate the fundamental mechanisms of the interaction of high energy photons with biological material surrounded by a liquid. Detection of radicals will be based on chemical scavenging methods that will be used to quantify the production of OH and HO2 radicals, under different irradiation conditions. In the first experiments, irradiation studies will be carried out in part with an up-graded version of an existing movable experimental set-up (IRAD set-up), which be upgraded with a microfluidic cell, and used under anaerobic conditions. Photo/Auger electron spectroscopy studies of liquids will utilize a new portable apparatus (MultiSpec Set-up), where a recycling liquid microjet will be used in vacuum. Recovering the irradiated sample is crucial for our project to be able to perform off-line analytical measurements (fluorescence yield, mass spectrometry) on the same sample measured by electron spectroscopy. We also plan to recycle sample in a closed loop system in order to progressively increase the average dose and follow its chemical evolution. Electron coincidence techniques will be used on the liquids to associate the photoelectron and Auger spectra, and thus have a better understanding of the effects of the environment during the decay processes of the initial core hole. Our studies will extend from pure water to solutions of sugar phosphates such as 5 ribose phosphate and 2-deoxyribose 5-monophosphate, a biomimetic molecule of the DNA backbone. A close collaboration with theoreticians will be a valuable component of the consortium. We will investigate the early stages of the dissociation of core ionized water or sugar-phosphate molecules, embedded in liquid water, at the femto to picosecond time scale, using ab initio Molecular Dynamics (MD) simulation. To support the experimental findings for the production of superoxide radicals in pure water, we will first model the dynamics induced by an oxygen-K ionization, starting from configurations in which one water molecule is doubly ionized and another one, localized within one nanometer, is singly ionized. Such an event is highly probable since, after Auger decay, the core-ionized water molecule will carry a double vacancy. Moreover, the photo and Auger electrons are ejected with a few hundred electronvolts kinetic energy and can ionize a neighbouring water molecule with a high probability since their mean free path is only a few nanometers in water. The results will be used as input data for the Kinetic Monte-Carlo simulation to extend to the chemistry occurring on a time scale of microseconds.