Ice-fourteen crystal structure

Ice XIV (Ice-fourteen)

Ice-fourteen (ice XIV) is the proton-ordered form of ice-twelve, formed by doping with 10 mM HCl (about one molecule to every 5000 molecules of water; as DCl with D₂O) below 118 K and at 1.2 GPa to facilitate the phase transition [1002]. The transformation is reversible with temperature change, but less proton-ordering of ice-fourteen is found at lower pressure [1081 ]. The crystals were orthorhombic P2₁2₁2₁ with cell dimensions a 8.350 Å, b 8.139 Å and c 4.083 Å (90°, 90°, 90°, 12 molecules; at atmospheric pressure and 80 K) and a unit cell contains 12 water molecules [1002]. 8 out of the 24 proton positions in the unit cell (as some labeled * opposite forming chains; the shown ordering of these is predominant) mostly remained disordered. Dielectric spectroscopy studies have shown that the transition from disordered ice-twelve to fully ordered ice-fourteen is composed of a fast component, yielding ≈ 20% of the expected entropy loss followed by a slow component achieving 60%, in the presence of HCl catalysis [2353 ]. Using a first-principles density functional theory method, the ice XIV theoretical Raman scattering, the infrared absorption spectrum, and the inelastic neutron scattering spectrum have been calculated [3490 ].

It is possible that two further metastable proton-ordered forms of ice XIV may form under kinetically controlled conditions, as shown by simulations [1105 ].

Interactive Jmol structures are given.

Ice-fourteen crystal structure Ice XIV (Ice-fourteen)

Ice-fourteen crystal structure

Ice XIV (Ice-fourteen)