Quantum Mechanical Effects on the Static Structure Factor of Pairs of Orthodeuterium Molecules

Neutron diffraction results on low density orthodeuterium gas at four densities along the 36.0 K isotherm are reported. The zero-density limit of the Fourier transform of the pair correlation function of this quantum mechanical system has been derived and computed both classically and quantum mechanically using a recently proposed intermolecular isotropic potential for hydrogen. The pure quantum effects on the static structure factor of the deuterium pair, mainly due to the diffraction of Boltzmann particles, have been thus measured. The comparison between experimental and theoretical results confirms the inadequacy of the classical description, while the quantum mechanical calculation gives a good account of the structural properties.