  The vibrational and structural properties of a hydrogen-rich Group IVa
hydride, Ge(CH$_3$)$_4$, are studied by combining Raman spectroscopy and
synchrotron X-ray diffraction measurements at room temperature and at pressures
up to 30.2 GPa. Both techniques allow the obtaining of complementary
information on the high-pressure behaviors and yield consistent phase
transitions at 1.4 GPa for the liquid to solid and 3.0, 5.4, and 20.3 GPa for
the solid to solid. The four high-pressure solid phases are identified to have
the cubic, orthorhombic, monoclinic and monoclinic crystal structures with
space groups of Pa-3 for phase I, Pnma for phase II, P2$_1$/c for phase III,
and P2$_1$ for phase IV, respectively. These transitions are suggested to
result from the changes in the inter- and intra-molecular bonding of this
compound. The softening of some Raman modes on CH$_3$ groups and their sudden
disappearance indicate that Ge(CH$_3$)$_4$ might be an ideal compound to
realize metallization and even high-temperature superconductivity at modest
static pressure for laboratory capability.
