HR: 0800h
AN: MR41A-0907    [Abstracts]
TI: Structure of the Hydrated (10-14) Surface of Rhodochrosite (MnCO₃)
AU: * Jun, Y
EM: kokoliko@gmail.com
AF: Department of Earth and Planetary Sciences, University of California-Berkeley, 307 McCone Hall, Berkeley, MA 94720 United States
AU: * Jun, Y
EM: kokoliko@gmail.com
AF: Geochemistry Department Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, MA 94720 United States
AU: Ghose, S K
EM: ghose@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, University of Chicago, 9700 South Cass Ave., Argonne, IL 60439 United States
AU: Trainor, T P
EM: fftpt@uaf.edu
AF: Department of Chemistry and Biochemistry, University of Alaska, PO Box 756160, Fairbanks, AK 99775 United States
AU: Eng, P J
EM: eng@cars.uchicago.edu
AF: Consortium for Advanced Radiation Sources, University of Chicago, 9700 South Cass Ave., Argonne, IL 60439 United States
AU: Eng, P J
EM: eng@cars.uchicago.edu
AF: James Franck Institute, Department of Physics, University of Chicago, 5747 S. Ellis Ave, Chicago, IL 60637 United States
AU: Martin, S T
EM: scot_martin@harvard.edu
AF: Division of Engineering and Applied Sciences, Harvard University, 29 Oxford St, Cambridge, MA 02138 United States
AB: The three-dimensional structure of the hydrated (10-14) surface of MnCO₃ is determined from the results of crystal-truncation rod (CTR) X-ray scattering. Ten specular and nonspecular rods were measured at 90% relative humidity and 298 K to provide both vertical and lateral sensitivity to the interfacial structure. The best-fit model constrained by the scattering data is a surface that has an oxygen overlayer. The distance from the oxygen in the overlayer to top-layer manganese is 2.600 ± 0.003 Å. The O and Mn in these layers have equal occupancies within error of 0.84. The oxygen overlayer has a well-defined lateral registry displaced by 0.16 Å and 0.63 Å in the x- and y-directions, respectively, from Mn atoms in the top layer. The carbonate groups in the top layer tilt by -4.15 ± 2.1 ° in phi_c (toward the surface plane) and 2.6 ± 1.2 ° in chi. The tilt of the second layer carbonate group is nearly zero within error for the best-fit model. The layer spacings for Mn atoms expand between the first and second layer and contract between the second and third layer. The layer spacings for C atoms from the CO₃ groups contract in both the first-second and second-third layers. The results provide a detailed atomic structure for the hydrated surface region on the surface of MnCO₃, and these results should provide a structural baseline for the interpretation of chemical reactivity and adsorption of metal ions and organic ligands on this surface.
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3947 Surfaces and interfaces
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005