NEUTRON DIFFRACTION FROM LOW-DENSITY CD4 GAS

The study of the density dependence of neutron diffraction spectra in dilute gases, already applied in recent papers to the determination of two- and three-body interaction properties in monatomic insulating fluids, is extended here to the case of a molecular fluid. Deuterated methane has been chosen for its good neutron scattering properties and its small molecular anisotropy. The centre-of-mass static structure factor S(Q) has been measured at four densities between 0.55nm-3 and 1.84nm-3 and at a temperature just below critical. Density analysis of the Fourier transform c(Q) of the direct correlation function makes it possible to show that valuable information on the intermolecular interactions is contained in the neutron data.