Observation of the fastest chemical processes in the radiolysis of water
Elementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. While numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, has remained elusive. We use tunable femtosecond soft x-ray pulses from an x-ray free electron laser to directly reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The strong, isolated resonance associated with the valence hole (H2O+/OH) enables straightforward detection. QM/MM calculations reveal that the x-ray spectra are sensitive to structural dynamics at the ionization site. We find signatures of hydrated-electron dynamics in the x-ray spectrum.