In situ Raman spectroscopy study on dissociation of methane at high temperatures and at high pressures

We investigate the stability and dissociation of methane, which is the most abundant organic molecule in the universe, using diamond anvil cell (DAC) with in situ Raman spectroscopy up to 903 K and 21 GPa. At the temperatures of 793 and 723 K and the corresponding pressures of 16.15 and 20.30 GPa, methane dissociates to form carbon 'soot' and heavier hydrocarbons involving C=C and C bonds. However, if the pressure is not very high, methane remains stability up to the highest temperature of 903K of the work. The four symmetric C-H bonds of methane split at high temperatures and at high pressures, and there is at least one phase transition of crystalline symmetry from face centred cubic (fcc) to hexagonal close packed (hcp) before dissociation.