HIGH-PRESSURE RAMAN STUDIES OF A NITROGEN-HELIUM MIXTURE UP TO 40 GPA

A He-N-2 mixture of 0.8 mole fraction He was investigated by high-pres sure Raman spectroscopy. The N-2 vibron in fluid He-N-2 is observed up to approximate to 9 GPa. Spectra of external and internal modes of th e van der Waals compound He(N-2)(11), which is formed above 9 GPa, wer e obtained up to 40 GPa. The similarities of the spectral features to those of epsilon-N-2 imply a close relationship between the structures of He(N-2)(11) and epsilon-N-2. The enhanced nu(2)/nu(1)-intensity ra tio suggests that He may substitute or displace N-2 molecules from the alpha site in the epsilon-phase. The observed splitting of the main v ibron of isotopic species N-14-N-15 indicates that in addition to fact or-group interactions site effects are responsible for the observed sp littings of the N-14(2) main vibron of He(N-2)(11).