Negative vibrational shift of nitrogen diluted in xenon at the fluid–solid transition

It is known from experimental evidence that the Raman shift of nitrogen and nitrogen in argon, measured as a function of the pressure at ambient temperature, reveals a positive jump at the transition from the liquid to the solid phase. Intuitively, this increase is sometimes attributed to the increase of density, but recently it has been shown that the change in order at the transition also plays a role. The present study deals with the behavior of nitrogen diluted in xenon. In this system, even a negative jump is found experimentally. Computer simulations on a model system for the $N2–Xe$ mixture make clear that in this case the effect of the change in order is opposite.