Neutron scattering by heavy water and ice under hydrostatic pressure of argon

The neutron diffraction study of the system argon-heavy water under pressur es of 100 and 300 MPa revealed the formation of clathrate argon hydrate (ty pe II structure, sp.gr. Fd (3) over bar m, a = 17.167 Angstrom at 283 K) an d the corresponding modifications of ice (ice Ih at 100 MPa and ice II at 3 00 MPa). The neutron diffraction patterns and the spectra of inelastic inco herent neutron scattering were obtained at temperatures up to 190 K. Possib le penetration of argon into the cavities of the crystal structure of ice I I is discussed. However, the available experimental data are insufficient f or either the confirmation of this assumption or for the determination of v oid occupancies with argon in this clathrate hydrate.