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

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 T ² + 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.