College Park, Maryland      June 6 - 10 , 2004

TP14: Neutron and Thermodynamic Investigation of Alkane Adsorption on MgO(100) Surfaces

R. E. Cook, S. Chanaa, M. J. Farinelli, P. N. Yaron (The University of Tennessee - Department of Chemistry), T. Arnold (Oak Ridge National Laboratory - Chemical Sciences Division), L. L. Daemen (Los Alamos Neutron Science Center, Los Alamos National Laboratory), T. Ramirez-Cuesta (ISIS, Rutherford Appleton Laboratory), S. Clarke (University of Cambridge - Department of Chemistry), J. Z. Larese (The University of Tennessee - Department of Chemistry; Oak Ridge National Laboratory - Chemical Sciences Division)

The adsorption properties of the first four members of the normal alkanes (methane, ethane, propane, butane) and films on the MgO (100) surface were investigated using neutron scattering and volumetric isotherm techniques. A series of high-resolution, adsorption isotherm measurements were performed using an automated adsorption apparatus. These data were used to determine both the two-dimensional isothermal compressibility and the isosteric heat of adsorption and to identify regions where phase transitions might occur. In all cases we find evidence for the presence of at least three layering transitions. We present our results to date of our investigations of the monolayer and multilayer solid phases using neutron diffraction and inelastic neutron spectroscopy (rotational and vibrational). Some preliminary indications of the nature of the dynamical properties of these solid phases will be presented by making comparisons of the neutron spectra with calculations of the molecular-vibrational modes. We will compare our results to other related experimental investigations where appropriate.

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