Pressure-Driven Reactivity in Dense Methane-Nitrogen Mixtures

Carbon, nitrogen, and hydrogen are among the most abundant elements in the solar system, and our understanding of their interactions is fundamental to prebiotic chemistry. CH4 and N2 are the simplest archetypical molecules formed by these elements and are both markedly stable under extremes of pressure. Through a series of diamond anvil cell experiments supported by density functional theory calculations, we observe diverse compound formation and unexpected reactivity in the dense CH4-N2 system. Above 7GPa two concentration-dependent molecular compounds emerge, (CH4)5N2 and (CH4)7(N2)8, held together by weak van der Waals interactions. Strikingly, further compression at room temperature irreversibly breaks the N2 triple bond, inducing the dissociation of CH4 above 140GPa, with the nearquenched samples revealing distinct spectroscopic signatures of strong covalently bonded C-N-H networks. High temperatures vastly reduce the required pressure to promote the reactivity between CH4 and N2, with NH3 forming together with longer-chain hydrocarbons at 14GPa and 670K, further decomposing into powdered diamond when temperatures exceed 1200K. These results exemplify how pressuredriven chemistry can cause unexpected complexity in the most simple molecular precursors.