Attosecond-pump attosecond-probe x-ray spectroscopy of liquid water.

Li, Shuai; Lu, Lixin; Bhattacharyya, Swarnendu; Pearce, Carolyn; Li, Kai; Nienhuis, Emily T; Doumy, Gilles; Schaller, R D et al. · Science · 2024

basic_science · Level V

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Abstract

Attosecond-pump/attosecond-probe experiments have long been sought as the most straightforward method for observing electron dynamics in real time. Although there has been much success with overlapped near-infrared femtosecond and extreme ultraviolet attosecond pulses combined with theory, true attosecond-pump/attosecond-probe experiments have been limited. We used a synchronized attosecond x-ray pulse pair from an x-ray free-electron laser to study the electronic response to valence ionization in liquid water through all x-ray attosecond transient absorption spectroscopy (AX-ATAS). Our analysis showed that the AX-ATAS response is confined to the subfemtosecond timescale, eliminating any hydrogen atom motion and demonstrating experimentally that the 1b<sub>1</sub> splitting in the x-ray emission spectrum is related to dynamics and is not evidence of two structural motifs in ambient liquid water.