The dissociation of methane hydrate at high pressure is studied by in situ Raman spectroscopy in a diamond-anvil cell. As for the Raman spectrum of sI methane hydrate, the v1 band of CH4 is split into two peaks v′1 and v″1, indicating the partitioning of CH4 between the large (51262) and small (512) cavities, respectively. With increasing temperature, the intensity ratio of Iv′1/Iv″1 decreases obviously, and the d(Iv′1/Iv″1)/dT is −0.079 K−1. Additionally, the v1 band of the dissolved CH4 is close to v″1 of the CH4 molecule engaged in the small 512 cavity. This implies that, in the initial stage of hydrate formation, the abundance of small 512 cavities is greater than that of large 51262 cavities.
Q. Sun and H. F. Zheng, "In Situ Raman Spectroscopic Study of the Dissociation of Methane Hydrate at High Pressure," Appl. Spectrosc. 60, 985-988 (2006)