180784.fig.003
Figure 3: Raman spectra of (a) ionic crystal at 2.8 GPa, (b) a mixture of ionic and molecular crystals at 2 GPa, and (c) molecular crystal at 1.7 GPa, showing the phase transition of molecular compound from ionic to neutral form. The assignment of the internal vibrational modes in (c) corresponds to symmetrical dimer [14].