Elucidating the guest disorder in structure II argon hydrate – A neutron diffraction isotopic substitution study

摘要: Abstract Clathrate hydrates with the cubic structure II (CS-II) form typically large guest molecules, such as tetrahydrofuran, trimethylamine oxide, or propane. However, CS-II is also realized for argon hydrate despite comparatively small van der Waals diameter of (around 3.8 ​A). Here, deuterated was studied at ambient pressure in temperature range 20–95 ​K using neutron diffraction and comparing natural Ar 36Ar, which scatters neutrons more than 13 times efficiently. The procedure allowed to unambiguously establish positional disorder within cages CS-II, while simultaneously refining host structures. These are singly occupied off-centered atoms distribute on two tetrahedron-shaped split positions a ratio 3:1. Molecular dynamics (MD) simulations revealed that crystallographic due mobile even 20 ​K. MD potential energy distribution confirmed model. It noted unit cell volumes investigated virtually identical N2 hydrate, has similar composition pressure, indicating very (slightly attractive) host-guest interaction.