Raman scattering spectroscopic study of n-pentane under high pressure

The Raman spectroscopy of n-pentane was investigated in a Moissanite anvil cell from 0.07 GPa to 4.77 GPa at ambient temperature. The result shows that the CH3 symmetric stretching vibration (2877 cm(-1)) and asymmetric stretching vibration (2964 cm(-1)), the CH2 symmetric stretching vibration (2856 cm(-1)) and asymmetric stretching vibration (2935 cm(-1)), and -(CH2)n- in-phase twist mode (1303 cm(-1)) shifted to higher wavenumbers almost linearly with increasing pressure. Around 2.4 GPa an abrupt visible change took place, indicating a sort of phenomenon of freezing due to over-pressurization. In the pressure range of 2.84 to 4.77 GPa a high-pressure phase transition may occur in the crystallized n-pentane. By determining pressure with the method of solid-liquid coexistence, we concluded that the equilibrium freezing pressure of n-pentane is 1.90 +/- 0.05 GPa at 27 degrees C.