Abstract
Molecular nitrogen exhibits one of the strongest known interatomic bonds, while xenon possesses a closed-shell electronic structure: a direct consequence of which renders both chemically unreactive. Through a series of optical spectroscopy and x-ray diffraction experiments, we demonstrate the formation of a novel van der Waals compound formed from binary Xe-N2 mixtures at pressures as low as 5 GPa. At 300 K and 5 GPa Xe(N2)2-I is synthesised, and if further compressed, undergoes a transition to a tetragonal Xe(N2)2-II phase at 14 GPa; this phase appears to be unexpectedly stable at least up to 180 GPa even after heating to above 2000 K. Raman spectroscopy measurements indicate a distinct weakening of the intramolecular bond of the nitrogen molecule above 60 GPa, while transmission measurements in the visible and mid-infrared regime suggest the metallisation of the compound at ~100 GPa.
Highlights
Molecular nitrogen exhibits one of the strongest known interatomic bonds, while xenon possesses a closed-shell electronic structure: a direct consequence of which renders both chemically unreactive
The application of high pressure can provide new synthesis routes, initiating chemical processes that would not happen otherwise, such as N2 becoming reactive with the noble metals, as in the formation of platinum or iridium nitrides[9,10]
The reactivity can be fundamentally altered with the application of high pressure, the process which has produced van der Waals compounds composed of Xe-H213 and Xe-O214, as well as a Xe-H2O clathrate[15]
Summary
We have studied the formation conditions and stability of xenon and nitrogen compounds up to pressures of 180 GPa in a diamond anvil cell (DAC). Solid Xe (99.9% purity) was initially cryogenically loaded into a DAC under a N2 atmosphere. Loading was confirmed initially through comparisons of white light transmission spectra due to the change in refractive index between the empty sample chamber and loaded sample. Thorough mapping of the sample with Raman spectroscopy was carried out to ensure no impurities were present in the sample and further confirmation was obtained through x-ray diffraction analysis. Equation of state data were determined using EosFIT 737. Fitted equation of state parameters for Xe(N2)2-I: V0 = 873(90) Å3, K0 = 47(56) GPa, K′= 1(5). Equation-of-state parameters for Xe(N2)2-II: V0 = 526(158) Å3, K0 = 9(14) GPa, K′= 4.5(11), K′′=−0.51131 GPa−1
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