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 (H₂). The measurements reveal the formation of a new molecular compound, with the approximate stoichiometry GeH₄ (H₂)₂, when the constituents are compressed above 7.5 GPa. Raman and infrared spectroscopic measurements show multiple H₂ vibrons substantially softened from bulk solid hydrogen. With increasing pressure, the frequencies of several Raman and infrared H₂ 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 H₂ molecules likely distributed between Oh and _Td sites. Above ca. 17 GPa, GeH₄ molecules in the compound become unstable with respect to decomposition products (Ge+ H₂), however, the compound can be preserved metastably to ca. 27 GPa for time-scales of the order of several hours.