  BiTeI is a giant Rashba spin splitting system, in which a non-centro
symmetric topological phase has recently been suggested to appear under high
pressure. We investigated the optical properties of this compound, reflectivity
and transmission, under pressures up to $15$ GPa. The gap feature in the
optical conductivity vanishes above $p \sim 9$ GPa and does not reappear up to
at least $15$ GPa. The plasma edge, associated with intrinsically doped charge
carriers, is smeared out through a phase transition at $9$ GPa. Using high
pressure Raman spectroscopy, we follow the vibrational modes of BiTeI,
providing additional clear evidence that the transition at 9 GPa involves a
change of crystal structure. This change of crystal structure possibly inhibits
the high-pressure topological phase from occurring.
