23:T416,

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 °C.

24:T470,

The Raman spectroscopy of n-heptane was investigated in a moissanite anvil cell at ambient temperatures and a diamond anvil cell under pressures of up to ∼2000 MPa and at temperature range from 298 to 588 K. The results show that at room temperature the vibration modes, assigned to the symmetric and antisymmetric stretching of CH₃ and CH₂ stretching, shifted to higher frequency according to quasi-linearity with increasing pressure, and a liquid–solid phase transition occurred at near 1150 MPa. The high-temperature solidus line of n-heptane follows a quadratic function of P = 0.00737 T² + 5.27977T – 1195.76556. Upon phase change, fitting the experimental data obtained in the temperature range of 183∼412 K to the Clausius–Clapeyron equation allows one to define the thermodynamic parameters of n-heptane of dP/dT = 0.01474T + 5.27977.

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Raman Scattering Spectroscopic Study of n -Pentane under High Pressure

In Situ High-Pressure and High-Temperature Experiments on n -Heptane