Origin of Two Distinct Peaks of Ice in the THz Region and Its Application for Natural Gas Hydrate Dissociation

For liquid water in the far-infrared spectrum, phonons of molecular vibrations constitute two bands with a narrow gap at around 30 meV. Interestingly, there are two distinct peaks for ice in this gap. We demonstrated that the two peaks come from two kinds of translational modes. Considering different O–O–O bending constants, we yielded two frequencies based on the ideal model of ice Ic. These two kinds of vibrational modes do not exist in liquid water due to the collapse of the rigid tetrahedral structure. Thus, a window remains for ice resonance absorption with minimum energy loss in liquid water. A new method to decompose gas hydrates was proposed by supplying two terahertz radiation energies at ∼6.8 and 9.1 THz. This is also applicable to flow assurance in gas pipelines, aircraft deicers, and so on. Experimental measurements are expected to verify this finding along with the rapid development of a THz laser.