Search

Abstract: To examine the nature of thermal motions of the CH4 molecules in the methane deuterohydrate (8CH4·46D2O), the scattering length density distribution was observed by the maximum entropy method (MEM) using neutron powder diffraction data measured in the temperature range of 7–185K. We drew the scattering-length density distribution as three dimensional graphic images and used the same isosurface level for all temperatures. The negative scattering length density, corresponding to the H atoms of CH4, was observed only in the large cage. The positive scattering length density attributed to the C atom of CH4 was observed at the center of each cage. With an increase in temperature, the negative and positive scattering length densities in the large cage disappear. The positive scattering length density remains at the center of the small cage regardless of temperature. These results strongly indicate that the motions of CH4 depend on the cage size and geometry. [Copyright &y& Elsevier]

Abstract: Crystal structures of carbon dioxide deuterohydrate were studied by neutron powder diffraction at temperatures from 10 to 200K. Maps of scattering length density distribution were obtained using a maximum entropy method (MEM), which clarified the motion of CO2 molecules in the hydrate. In small cages, the carbon atom of the CO2 molecule is at the center of the cage, and the oxygen atoms of CO2 revolve freely around the carbon atom. In large cages, the carbon atom also is at the center of the cage, but the oxygen atoms tend to revolve around the carbon atom along the plane parallel to the hexagonal facets of the cage. [Copyright &y& Elsevier]