Quantum mechanical effects on the static structure factor of pairs of orthodeuterium molecules

Neutron diffraction results on low density orthodeuterium gas at four densi ties along the 36.0 K isotherm are reported. The zero-density limit of the Fourier transform of the pair correlation function of this quantum mechanic al system has been derived and computed both classically and quantum mechan ically using a recently proposed intermolecular isotropic potential for hyd rogen. The pure quantum effects on the static structure factor of the deute rium 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 mec hanical calculation gives a good account of the structural properties.