CAGE OCCUPANCY AND COMPRESSIBILITY OF DEUTERATED N-2-CLATHRATE HYDRATE BY NEUTRON-DIFFRACTION

This paper reports pressure dependent high resolution neutron diffract ion work on N-2-clathrates, which for the first time provides numbers on the compressibility as well as the location and degree of filling o f the guest molecules in the small and large cages. N-2-clathrates cry stallize, at least at lower pressures and temperatures near 0 degrees C, in the Stackelberg type II structure. However, during the diffracti on experiments we have observed the transient and partial formation of the von Stackelberg type I N-2-clathrate at pressures exceeding sever al hundred bar. The filling of the small cages in the type II clathrat e roughly follows a Langmuir isotherm, In contrast to most previous as sumptions there is strong evidence that the large cages are doubly occ upied in both type I and type II N-2-clathrates. The observed filling can be fitted reasonably well by a two-constant Langmuir model.