  High-pressure infrared transmission measurements on \PhC60 were performed up
to 9 GPa over a broad frequency range (200 - 20000 cm$^{-1}$) to monitor the
vibrational and electronic/vibronic excitations under pressure. The four
fundamental T$_{1u}$ modes of \C60a\ are split into doublets already at the
lowest applied pressure and harden with increasing pressure. Several cation
modes and fullerene-related modes split into doublets at around 2 GPa, the most
prominent one being the G$_{1u}$ mode. The splitting of the vibrational modes
can be attributed to the transition from the dynamic to static Jahn-Teller
effect, caused by steric crowding at high pressure. Four absorption bands are
observed in the NIR-VIS frequency range. They are discussed in terms of
transitions between LUMO electronic states in \C60a, which are split because of
the Jahn-Teller distortion and can be coupled with vibrational modes. Various
distortions and the corresponding symmetry lowering are discussed. The observed
redshift of the absorption bands indicates that the splitting of the LUMO
electronic states is reduced upon pressure application.
