PNNL

Abstract

Attosecond-pump/attosecond-probe experiments have long been sought as the most straightforward method to observe electron dynamics in real time. While numerous attosecond science successes have been achieved with overlapped near infrared femtosecond and extreme ultraviolet attosecond pulses combined with sophisticated theory, true attosecond-pump/attosecond-probe experiments have been limited due to the low intensity of commonly available attosecond pulses. We use a tunable, synchronized attosecond x-ray pulse pair from an x-ray free electron laser to study the initial electronic response to valence ionization in liquid water via all x-ray attosecond transient absorption spectroscopy (AX-ATAS). Our analysis shows that the AX-ATAS response is confined to the subfemtosecond timescale, thus eliminating any hydrogen atom motion and allowing us to demonstrate experimentally that the 1b1 splitting in the x-ray emission spectrum is not evidence for the existence of two structural motifs of liquid water at room temperature.