Two-Component Dynamics and the Liquidlike to Gaslike Crossover in Supercritical Water

PH Sun and JB Hastings and D Ishikawa and AQR Baron and G Monaco, PHYSICAL REVIEW LETTERS, 125, 256001 (2020).

DOI: 10.1103/PhysRevLett.125.256001

Molecular-scale dynamics in sub- to supercritical water is studied with inelastic x-ray scattering and molecular dynamics simulations. The obtained longitudinal current correlation spectra can be decomposed into two main components: a low-frequency (LF), gaslike component and a high- frequency (HF) component arising from the O-O stretching mode between hydrogen-bonded molecules, reminiscent of the longitudinal acoustic mode in ambient water. With increasing temperature, the hydrogen-bond network diminishes and the spectral weight shifts from HF to LF, leading to a transition from liquid- to gaslike dynamics with rapid changes around the Widom line.

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