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arXiv · 2110.07490

Structure and vibrational properties of methane up to 71 GPa

Maxim Bykov·Elena Bykova·Chris J. Pickard·Miguel Martinez-Canales·Konstantin Glazyrin·Jesse S. Smith·Alexander F. Goncharov
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Abstract

Single-crystal synchrotron X-ray diffraction, Raman spectroscopy, and first principles calculations have been used to identify the structure of the high-pressure (HP) phase of molecular methane above 20 GPa up to 71 GPa. The structure of HP phase is trigonal R3, which can be represented as a distortion of the cubic phase B, previously documented at 7-15 GPa and confirmed here. The positions of hydrogen atoms in HP phase have been 19 obtained from first principles calculations. The molecules occupy four different crystallographic sites in phases B and eleven sites in the HP phase, which result in splitting of molecular stretching modes detected in Raman spectroscopy and assigned here based on 22 a good agreement with the Raman spectra calculated from the first principles.

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Maxim Bykov, Elena Bykova, Chris J. Pickard, Miguel Martinez-Canales, Konstantin Glazyrin, Jesse S. Smith, Alexander F. Goncharov. 2021-10-14. Structure and vibrational properties of methane up to 71 GPa. https://doi.org/10.1103/physrevb.104.184105

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