Abstract
The ultrafast structural dynamics of water following inner-shell ionization is a crucial issue in high-energy radiation chemistry. We have exposed isolated water molecules to a short x-ray pulse from a free-electron laser and detected momenta of all produced ions in coincidence. By combining experimental results and theoretical modeling, we can image dissociation dynamics of individual molecules in unprecedented detail. We reveal significant molecular structural dynamics in H2O2+, such as asymmetric deformation and bond-angle opening, leading to two-body or three-body fragmentation on a timescale of a few femtoseconds. We thus reconstruct several snapshots of structural dynamics at different time intervals, which highlight dynamical patterns that are relevant as initiating steps of subsequent radiation-damage processes.10 MoreReceived 25 March 2021Revised 20 July 2021Accepted 16 September 2021DOI:https://doi.org/10.1103/PhysRevX.11.041044Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasAutoionization & Auger processesElectronic excitation & ionizationPhotodissociationPhotoemissionSingle- and few-photon ionization & excitationPhysical SystemsMoleculesTechniquesAb initio calculationsHartree-Fock methodsPhotoionizationX-ray photoelectron spectroscopyAtomic, Molecular & Optical
Highlights
The response of water to ionizing radiation and the accompanying formation of ions and/or radicals is a key question for many research areas, such as radiation damage in biological tissue [1], radio-oncology [2], and corrosion in nuclear reactors [3]
The dynamics of core ionization and core excitation in liquid water have been studied via fluorescence [11,12] and Auger spectroscopy [13]
The full characterization of its fragmentation dynamics, including both structural and timing information, and involving the whole ensemble of dicationic states reached after core ionization and Auger decay, is of immediate relevance for the understanding of subsequent radiation chemistry processes
Summary
The response of water to ionizing radiation and the accompanying formation of ions and/or radicals is a key question for many research areas, such as radiation damage in biological tissue [1], radio-oncology [2], and corrosion in nuclear reactors [3]. The abundance of ion fragments and their asymptotic momenta produced by core exciting and/or core ionizing an isolated H2O molecule have been studied by ion-mass spectroscopy [14] or ion/ion-electron coincidence measurements [7,14]. While these techniques allow identification of the produced fragments, they do not shed full light on the temporal evolution of the dissociation events. The full characterization of its fragmentation dynamics, including both structural and timing information, and involving the whole ensemble of dicationic states reached after core ionization and Auger decay, is of immediate relevance for the understanding of subsequent radiation chemistry processes. That evolution is traced at different time intervals thanks to a combination of experimental advances and theoretical modeling
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