Vibrational dynamics, intermolecular interactions, and compound formation in GeH4-H2 under pressure

Optical microscopy, spectroscopic and x-ray diffraction studies at high-pressure are used to investigate intermolecular interactions in binary mixtures of germane (GeH4)+hydrogen (H-2). The measurements reveal the formation of a new molecular compound, with the approximate stoichiometry GeH4(H-2)(2), when the constituents are compressed above 7.5 GPa. Raman and infrared spectroscopic measurements show multiple H-2 vibrons substantially softened from bulk solid hydrogen. With increasing pressure, the frequencies of several Raman and infrared H-2 vibrons decrease, indicating anomalous attractive interaction for closed-shell, nonpolar molecules. Synchrotron powder x-ray diffraction measurements show that the compound has a structure based on face-centered cubic (fcc) with GeH4 molecules occupying fcc sites and H-2 molecules likely distributed between O-h and T-d sites. Above ca. 17 GPa, GeH4 molecules in the compound become unstable with respect to decomposition products (Ge+H-2), however, the compound can be preserved metastably to ca. 27 GPa for time-scales of the order of several hours. (C) 2010 American Institute of Physics. [doi:10.1063/1.3505299]