Speaker
Description
Understanding the elementary steps following ionization in aqueous systems provides a framework for radiation-matter interactions in chemistry and biology. Radiation chemistry has been largely explored on picosecond timescales through pulse radiolysis - a timescale which precludes mechanistic understanding of the birth of reactive species. Synchronized, two-color sub-femtosecond x-ray pulses from x-ray free-electron lasers [1] provide a qualitatively new approach to track the electronic and nuclear dynamics following ionization. We studied radiation-induced processes in pure liquid water via x-ray transient absorption in the water window, first following outer-valence ionization [2] and then following full-valence ionization [3]. The latter represents the first attosecond pump/attosecond probe experiment on a condensed phase sample and introduced the technique of all x-ray attosecond transient absorption (AX-ATAS). In condensed phase AX-ATAS we find a strong influence of electron collisional ionization and weaker effects from electronic coherence . Interestingly, the latter study demonstrates the ability of attosecond pump/probe experiments to reveal information on equilibrium properties and resolves a controversy surrounding the interpretation of x-ray emission spectra as evidence for two structural motifs of liquid water. Beyond pure liquid water, studies of aqueous salt solutions are being studied and initial results will be presented.
[1] Z. Guo et al., Nat. Photonics 18, 691–697 (2024).
[2] Z.-H. Loh et al., Science 367, 179–182 (2020).
[3] S. Li et al., Science 383, 1118-1122 (2024).
