Ultrafast X-ray absorption spectroscopy is applied to study the conversion of longitudinal to transverse phonons in aqueous solution. Permanganate solutes serve as X-ray probe molecules that permit the measurement of the conversion of 13.5 GHz, longitudinal phonons to 27 GHz, transverse phonons that propagate with high-frequency sound speed. The experimental results, combined with QM/MM MD simulations, show that the hydrogen bond network around the charged solutes has a glass-like stiffness that persists for at least tens of picoseconds.
Jiao, Y., Adams, B. W., Dohn, A. O., Møller, K. B., Jonsson, H., & Rose-Petruck, C. (2017). Ultrafast X-ray absorption study of longitudinal-transverse phonon coupling in electrolyte aqueous solution. Physical Chemistry Chemical Physics, 19(40), 27266-27274. https://doi.org/10.1039/c7cp02978k