Novel van der Waals Compounds in the Nitrogen-Methane Binary System at Room Temperature and High Pressure

Abstract

Beginning in the early 1990's, the study of binary mixtures containing simple molecules under high pressure led to the discovery of a solid van der Waals compound: a weakly bound molecular solid whose cohesion is primarily due to van der Waals forces. The formation of this type of compound, such as He(N2)11 discovered in 1992 in the helium-nitrogen system by Vos et al. [Vos, 1992], is predicted in systems such as those containing nitrogen and methane. The nitrogen-methane binary system is studied at room temperature under high pressure in order to construct the pressure-concentration phase diagram up to 16 GPa. Over 20 mixtures of varying concentration have been studied within a diamond anvil cell through Raman spectroscopy and powder X-ray diffraction using synchrotron radiation. Within the phase diagram, phases exist that resemble the pure species at similar thermodynamic conditions, and additionally, two novel van der Waals compounds are observed.