Ne- and O₂-filled ice XVII: a neutron diffraction study

Deuterated ice XVII, a metastable solid water polymorph, was filled with Ne and O2 at p ≈ 100 kPa and studied by in situ neutron diffraction (ILL, France). Powder patterns were collected in the ranges of 20-50 K (Ne) and 4.6-90 K (O2). Rietveld refinement and difference Fourier techniques showed that the gas molecules were located inside the hexagonal channels of the host ice. Both Ne atoms and O2 molecules are arranged in a spiral-like configuration off the channel axis, preserving the P6122 symmetry of the host in the case of Ne, but reducing it to P61 in O2. A larger Ne absorption compared to Ne-filled ice II is observed, which is consistent with longer host-guest contacts producing smaller hydrophobic repulsion. In O2-filled ice XVII, instead, short O-D distances (2.37 Å) have attractive character and stabilize the structure.