Stability of Ar(H<sub>2</sub>)<sub>2</sub> to 358 GPa.
basic_science · Level V
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- Record sourced from PubMed, PMID 28289218.
- Also identified by DOI 10.1073/pnas.1700049114 and PMC identifier 5389335.
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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(H<sub>2</sub>)<sub>2</sub>, a hydrogen-rich compound with molecular hydrogen, to explore the effect of "doping" on the intermolecular interaction of H<sub>2</sub> molecules and metallization at ultrahigh pressure. Ar(H<sub>2</sub>)<sub>2</sub> was 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(H<sub>2</sub>)<sub>2</sub> retains 2-eV bandgap and H<sub>2</sub> molecular units up to 358 GPa. This is attributed to reduced intermolecular interactions between H<sub>2</sub> molecules in Ar(H<sub>2</sub>)<sub>2</sub> compared with that in solid H<sub>2</sub> A 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(H<sub>2</sub>)<sub>2</sub> provide direct insight into the structure and bonding of this hydrogen-rich system, suggesting a negative chemical pressure on H<sub>2</sub> molecules brought about by doping of Ar.