Microscopic collective dynamics in liquid neon-deuterium mixtures: Inelastic neutron scattering and quantum simulations

In this paper a combined neutron scattering and quantum simulation study of the collective dynamics in liquid Ne-D2 mixtures, at a temperature of T = 30 K and in the wave-vector transfer range 4 nm^-1 < q < 51 nm^-1, is presented. Two D2 concentrations are investigated, one close to 25% molar and the other close to 50% molar, together with pure Ne. The dynamic structure factor for the centers of mass of the two molecular species is extracted from the neutron scattering data and subsequently compared with that obtained from three different quantum simulation methods, such as ring polymer molecular dynamics and two slightly different versions of the Feynman-Kleinert approach. A general agreement is found, even though some discrepancies both among simulations, and between simulations and experimental data, can be observed. In order to clarify the physical meaning of the present spectroscopic results, an analysis of the longitudinal current spectral maxima is carried out showing the peculiarities of the D_2 center-of-mass dynamics in these mixtures. A comparison with the centroid molecular dynamics results obtained for the D_2 center-of-mass self-dynamics in the same liquid mixtures is finally proposed.