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 flu ids, is extended here to the case of a molecular fluid. Deuterated met hane has been chosen for its good neutron scattering properties and it s small molecular anisotropy. The centre-of-mass static structure fact or S(Q) has been measured at four densities between 0.55 nm(-3) and 1. 84 nm(-3) and at a temperature just below critical. Density analysis o f the Fourier transform c(Q) of the direct correlation function makes it possible to show that valuable information on the intermolecular in teractions is contained in the neutron data.