title: Stability of Ar(H2)2to 358 GPa.
abstract: "Chemical precompression" through introducing impurity atoms into hydrogen has been proposed as a method to facilitate metallization of hydrogen under external pressure. Here we selected Ar(H2)2, a hydrogen-rich compound with molecular hydrogen, to explore the effect of "doping" on the intermolecular interaction of H2molecules and metallization at ultrahigh pressure. Ar(H2)2was studied experimentally by synchrotron X-ray diffraction to 265 GPa, by Raman and optical absorption spectroscopy to 358 GPa, and theoretically using the density-functional theory. Our measurements of the optical bandgap and the vibron frequency show that Ar(H2)2retains 2-eV bandgap and H2molecular units up to 358 GPa. This is attributed to reduced intermolecular interactions between H2molecules in Ar(H2)2compared with that in solid H2A splitting of the molecular vibron mode above 216 GPa suggests an orientational ordering transition, which is not accompanied by a change in lattice symmetry. The experimental and theoretical equations of state of Ar(H2)2provide direct insight into the structure and bonding of this hydrogen-rich system, suggesting a negative chemical pressure on H2molecules brought about by doping of Ar.
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China.|High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439.
authors.forename: Cheng
authors.initials: C
authors.lastname: Ji
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015.|Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China.
authors.forename: Alexander F
authors.initials: AF
authors.lastname: Goncharov
authors.affiliation: Condensed Matter Theory, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, S-75120 Uppsala, Sweden.
authors.forename: Vivekanand
authors.initials: V
authors.lastname: Shukla
authors.affiliation: Condensed Matter Theory, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, S-75120 Uppsala, Sweden.
authors.forename: Naresh K
authors.initials: NK
authors.lastname: Jena
authors.affiliation: High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Popov
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China.|Center for the Study of Matter at Extreme Conditions, Department of Mechanical and Materials Engineering, Florida International University, Miami, FL 33199.|High Pressure Synergetic Consortium, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439.
authors.forename: Bing
authors.initials: B
authors.lastname: Li
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China.|Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015.
authors.forename: Junyue
authors.initials: J
authors.lastname: Wang
authors.affiliation: High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439.
authors.forename: Yue
authors.initials: Y
authors.lastname: Meng
authors.affiliation: Center for Advanced Radiation Sources, University of Chicago, Argonne, IL 60439.
authors.forename: Vitali B
authors.initials: VB
authors.lastname: Prakapenka
authors.affiliation: High Pressure Collaborative Access Team, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439.
authors.forename: Jesse S
authors.initials: JS
authors.lastname: Smith
authors.affiliation: Condensed Matter Theory, Materials Theory Division, Department of Physics and Astronomy, Uppsala University, S-75120 Uppsala, Sweden.
authors.forename: Rajeev
authors.initials: R
authors.lastname: Ahuja
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China.|High Pressure Synergetic Consortium, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439.
authors.forename: Wenge
authors.initials: W
authors.lastname: Yang
authors.affiliation: Center for High Pressure Science and Technology Advanced Research, Shanghai 201203, China; hmao@ciw.edu.|Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015.
authors.forename: Ho-Kwang
authors.initials: HK
authors.lastname: Mao
keywords: hydrogen-rich compound; intermolecular interaction; metallization; ultrahigh pressure