THE ORIENTATIONAL AND STRUCTURAL PROPERTIES OFN2andN2–AR SOLIDS AT HIGH PRESSURE

The high pressure phases ofN2andN2–Ar mixed solids at 7 GPa have been investigated using Monte Carlo simulations. Orientational order parameters and displacements of the molecules with respect to the positions of the space group were calculated. These tools provide an appropriate way to study these solids. In theε*phase, the displacementΔof theesites was found to be 0.05 Å. In the$\delta^*_{\rm loc}$phase, the orientational confinement to a disk of theN2molecules at thecsites increases with Ar concentration. Within this disk, the distribution is nonuniform, even at high temperatures. The orientationally ordered disk molecules show a displacement along the line of closest intermolecular contact. For the tetragonal modification of the$\delta^*_{\rm loc}$phase, thecaxis is perpendicular to these ordered and displaced disks. At high Ar concentrations, the$\delta^*_{\rm oo}$phase shows a large degree of alignment of the disk molecules. In this phase, the equilibrium positions show a complicated structure. Therefore, there are small but significant structural changes between the$\delta^*_{\rm loc}$,$\delta^*_{\rm rot}$and$\delta^*_{\rm oo}$phases.