Raman spectra of hydrocarbons under extreme conditions of pressure and temperature: a first-principles study

TL;DR

This study uses first-principles simulations to calculate Raman spectra of hydrocarbons under extreme pressure and temperature, aiding interpretation of experimental data relevant to Earth's deep carbon cycle and planetary science.

Contribution

It introduces a method combining ab initio molecular dynamics and polarization theory to accurately simulate Raman spectra of hydrocarbons at high P-T conditions, including anharmonic effects.

Findings

Identified characteristic Raman modes for C-C and C-C-C bonds.

Analyzed pressure and temperature effects on Raman bands.

Provided data to interpret in-situ Raman measurements at extreme conditions.

Abstract

Hydrocarbons are of great importance in carbon-bearing fluids in deep Earth and in ice giant planets at extreme pressure (P)-temperature (T) conditions. Raman spectroscopy is a powerful tool to study the chemical speciation of hydrocarbons; however, it is challenging to interpret Raman data at extreme conditions. Here, we performed ab initio molecular dynamics simulations coupled with the modern theory of polarization to calculate Raman spectra of methane, ethane, and propane up to 48 GPa and 2000 K. Our method includes anharmonic temperature effects. We studied the pressure and temperature effects on the Raman bands, and identified the characteristic Raman modes for the C-C and C-C-C bonds. Our result may help to interpret in-situ Raman data of hydrocarbons at extreme P-T conditions, with important implications for understanding the deep carbon cycle inside Earth and the compositions of ice giant planets.