Neutron Brillouin Scattering in Dense Nitrogen Gas

Computer simulations and theoretical calculations show that the van Hove scattering function for 0.3 < Q < 3 nm-1 is an important test case for theories of dense fluids. To study this region experimentally we have assembled a new neutron spectrometer system, which operates efficiently over this range. With this system we have measured the scattering from dense nitrogen gas at wave numbers from 0.5 to 1.5 nm-1. These results are compared to the Navier-Stokes and generalized hydrodynamics theories. At our lowest momentum transfers these two theories merge with one another and agree with the data. As the momentum transfer is increased the peaks broaden in frequency, the theories diverge from one another and this divergence can be studied experimentally for the first time.