High-pressure Raman investigation of mutual solubility and compound formation in Xe-N-2 and Ne-N-2

In this study, the mixed solid phases of the molecular systems Xe-N-2 and N e-N-2 have been investigated up to 13 GPa using Raman spectroscopy and so-c alled v-T and p-T scans. Both systems show a rich variety of solid phases. In Xe-N-2 a van der Waals compound has been found. The solubility of N-2 in solid Xe is about 7.5 mol %, while the solubility of the larger Xe atoms i nto the beta and delta phases of N-2 is higher. In Ne-N-2 two van der Waals compounds have been detected. The Raman spectrum of one of these compounds is very similar to that of He(N-2)(11). N-2 does not dissolve into solid N e, while Ne does dissolve into the beta and delta phases of N-2 even though the atomic diameter of Ne is considerably smaller than the molecular one o f N-2. Analogous to Ar-N-2, the Ne and Xe atoms are mainly located at the a sites in the delta* phase. For Ne-N-2, in contrast to Xe-N-2, the beta*-de lta* transition shifts to higher pressure. The epsilon*-delta* transition i s not shifted for Ne-N-2. The results have been compared with computer simu lations and analytical theories for hard-sphere systems. It is shown that t he ratio of the diameters of the molecules, alpha, is only a very rough ind ication for the phase behavior of mixed molecular systems at high pressure. [S0163-1829(99)08641-5].