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arXiv · 2311.07774

Speed of sound in methane under conditions of planetary interiors

Thomas G. White·Hannah Poole·Emma E. McBride·Matthew Oliver·Adrien Descamps·Luke B. Fletcher·W. Alex Angermeier·Cameron H. Allen·Karen Appel·Florian P. Condamine·Chandra B. Curry·Francesco Dallari·Stefan Funk·Eric Galtier·Eliseo J. Gamboa·Maxence Gauthier·Peter Graham·Sebastian Goede·Daniel Haden·Jongjin B. Kim·Hae Ja Lee·Benjamin K. Ofori-Okai·Scott Richardson·Alex Rigby·Christopher Schoenwaelder·Peihao Sun·Bastian L. Witte·Thomas Tschentscher·Ulf Zastrau·Bob Nagler·J. B. Hastings·Giulio Monaco·Dirk O. Gericke·Siegfried H. Glenzer·Gianluca Gregori
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Abstract

We present direct observations of acoustic waves in warm dense matter. We analyze wave-number- and energy-resolved x-ray spectra taken from warm dense methane created by laser heating a cryogenic liquid jet. X-ray diffraction and inelastic free-electron scattering yield sample conditions of 0.3$\pm$0.1 eV and 0.8$\pm$0.1 g/cm$^3$, corresponding to a pressure of $\sim$13 GPa. Inelastic x-ray scattering was used to observe the collective oscillations of the ions. With a highly improved energy resolution of $\sim$50 meV, we could clearly distinguish the Brillouin peaks from the quasielastic Rayleigh feature. Data at different wave numbers were utilized to derive a sound speed of 5.9$\pm$0.5 km/s, marking a high-temperature data point for methane and demonstrating consistency with Birch's law in this parameter regime.

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Thomas G. White, Hannah Poole, Emma E. McBride, Matthew Oliver, Adrien Descamps, Luke B. Fletcher, W. Alex Angermeier, Cameron H. Allen, Karen Appel, Florian P. Condamine, Chandra B. Curry, Francesco Dallari, Stefan Funk, Eric Galtier, Eliseo J. Gamboa, Maxence Gauthier, Peter Graham, Sebastian Goede, Daniel Haden, Jongjin B. Kim, Hae Ja Lee, Benjamin K. Ofori-Okai, Scott Richardson, Alex Rigby, Christopher Schoenwaelder, Peihao Sun, Bastian L. Witte, Thomas Tschentscher, Ulf Zastrau, Bob Nagler, J. B. Hastings, Giulio Monaco, Dirk O. Gericke, Siegfried H. Glenzer, Gianluca Gregori. 2024-05-03. Speed of sound in methane under conditions of planetary interiors. https://doi.org/10.1103/physrevresearch.6.l022029

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