Structural and spectroscopic studies of nitrogen-carbon monoxide mixtures: Photochemical response and observation of a novel phase

摘要

Mixtures of nitrogen and carbon monoxide in two molar compositions (90-10 and 95-5 N-2-CO) have been studied with Raman spectroscopy, X-ray diffraction, and first-principles density functional theory. Near 16 GPa, there is a discontinuous change in the X-ray diffraction patterns indicating a transition to phase I, which is distinct from any known phase of nitrogen. With the help of theory, the Xray diffraction pattern was indexed to a triclinic unit cell. The evolutionary crystal structure search also identified several metastable stoichiometries of C-O-N phases, which produce distinct signatures in the experimental Raman spectra, thus explaining anomalous Raman behavior. Decompression studies showed that phase I did not persist below the melt line of nitrogen and, as such, it can be concluded that all observations are reversible.