High pressure chemistry of CO-doped N2 crystals

Nitrogen rich materials and in particular poly-nitrogen systems are extremely appealing for their property of combining high energetic content with low environmental impact related to the release of N2. Nevertheless, despite a wealth of exotic fascinating molecules containing only N atoms has been predicted by calculations[1], up to now only systems with no more than 5 consecutive N atoms have been synthesized[2], with the only remarkable exception of cubic gauche nitrogen (110 GPa and 2000 K in a laser heated DAC), which could be recovered in a metastable form only down to 42 GPa at ambient T[3]. Here we report an experimental study in mDAC on the high pressure photochemistry of mixtures of CO and N2 (5% and 10% of CO) at 6.9, 10.0 and 26.0 GPa. Taking advantage of the substitutional doping of the N2 crystal, CO was used both as a photochemical activator, for triggering reactivity at low P and ambient T, and as a stabilizing molecular moiety, for high nitrogen content reaction products. FTIR and Raman spectra indicate that the reaction is triggered by the pressure induced formation of poly-CO clusters[4], whose photo-excitation is responsible for the involvement of the N2 molecules in the reactive process and for the incorporation of N atoms in the reaction product along different reaction mechanisms according to the reaction pressure. The reaction product exhibited photo-induced decomposition properties with the release of CO2 and N2 and could be retained down to 1-2 GPa at ambient pressure, suggesting potential applications as energetic material. The details of the reaction mechanism are supported by DFT calculations.