Figure 8: Raman spectra of crystalline PQ as a function of pressure: normal pressure, 1 atm (a); 2 × 103 atm (b); 22 × 103 atm (c); 35 × 103 atm (d); 1 atm (e), at the end of pressure cycle. The low and high frequency regions are normalized separately to their highest bands. A region between 1300–1370 cm−1, exhibiting a strong Raman peak from diamond culets, was removed.