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We have used synchrotron x-ray and Raman spectroscopic studies combined with molecular dynamics to investigate the I2 - H2 system at high pressure. By laser heating the mixture above 25 GPa we synthesized the molecular compound HI ( H2 )13 , with the A B 13 structure type and unusually high volumetric hydrogen content. The isolation of HI molecules by ( H2 )13 supramolecular clusters stabilizes the compound over a remarkable pressure range from 9 to at least 130 GPa. At lower pressures and 300 K another compound, hydrogen diiodane H2 ( HI)2 , spontaneously forms, being stable up to 12.5 GPa. [ABSTRACT FROM AUTHOR]

Through high-pressure Raman spectroscopy and x-ray diffraction experiments, we have investigated the formation, stability field, and structure of hydrogen iodide (HI). Hydrogen iodide is synthesized by the reaction of molecular hydrogen and iodine at room temperature and at a pressure of 0.2 GPa. Upon compression, HI solidifies into cubic phase I, and we present evidence for the emergence of a phase I' above 3.8 GPa. Across the wide temperature regime presented here, HI is unstable under compression (11 GPa at 300 K, 18 GPa at 77 K), decomposing into its constituent elements, after which no further reaction between hydrogen and iodine was observed up to pressures of 60 GPa. This study provides both the constraints on the phase diagram of HI and its kinetic stability. [ABSTRACT FROM AUTHOR]