The proposing team has a well established experience in the study on samples containingH_2 and D_2. Our recent neutron spectroscopic results on sII and sH H_2-filled clathrate hydrates, obtained on TOSCA, allowed to investigate the quantum dynamics of the guest H_2 molecules inside the host cages. This proposal now aims to study a new compound (named C_0 filled ice) still formed by H_2/D_2 and D_2O, but having a totally different crystal structure, analogous to that of alpha-quartz. This system might have a relevance from the perspective of new materials suitable for H_2 storage applications, since it can contain a large amount of H_2. Thus we propose to perform neutron diffraction on powder samples of C_0 (D_2O + D_2 or H_2 or HD), and to analyze the data through Rietveld refinement, so to accurately determine the positions of the atoms in the unit cell.