The vibrons nu ₁ and nu ₂ of N₂ 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 N₂-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 -N₂ at high pressures.