Detection of the epsilon - delta phase transition in N2and a N2-He mixture by Raman spectroscopy: new evidence for the solubility of fluid He in solid N2

The vibrons nu 1 and nu 2 of N 2 have been measured around the epsilon - delta phase transition by Raman spectroscopy. Thus, for the first time the epsilon - delta transition could be detected in this way. The Raman shift of the nu 1 -peak has been observed to be larger in the epsilon -phase than in the delta -phase and the Raman shift of the nu 2 -peak smaller. More importantly, this feature has also been observed in the mixture N 2 -He with 9.2 mol.% He around the phase transition at p=60 kbar and T=245 K, which is new evidence for a considerable temperature and pressure shift of the epsilon - delta phase transition line in the mixture and also for the solubility of fluid He in solid epsilon -N 2 at high pressures.