  We performed Raman and infrared (IR) spectroscopy measurements of hydrogen at
295 K up to 280 GPa at an IR synchrotron facility of SSRF. To reach the highest
pressure, hydrogen was loaded into toroidal diamond anvils with 40 micrometers
central culet. The intermolecular coupling has been determined by concomitant
measurements of the IR and Raman vibron modes. In phase IV, we find that the
intermolecular coupling is much stronger in the graphene (G) like layer of
elongated molecules compared to the Br2 like layer of shortened molecules and
it increases with pressure much faster in the G layer compared to the Br2
layer. These heterogeneous lattice dynamical properties are unique features of
highly fluxional hydrogen phase IV.
