title: Structure of the hydrated (1014) surface of rhodochrosite (MnCO3).
abstract: The three-dimensional structure of the hydrated (1014) surface of MnCO3 at 90% relative humidity and 295 K is determined from measurements of X-ray scattering along ten crystal-truncation rods (CTRs). The scattering data provide both vertical and lateral information about the interfacial structure. The model that best fits the scattering data is a surface having a first layer of manganese carbonate and an overlayer of oxygen (as water). Within the measurement uncertainty, the overlayer of oxygen (O(w)) and the first-layer of manganese (Mn1) have equal occupancies of 0.84. The Mn1-O(w) distance between these layers is 2.59 +/- 0.04 angstroms. The overlayer O atoms are displaced laterally by 0.157 angstroms in the x- and 0.626 angstroms in the y-direction relative to the first-layer Mn atoms. The first-layer carbonate groups tilt by -4.2 +/- 2.1 degrees in phi (toward the surface plane) and -2.6 +/- 1.2 degrees in chi (an axis perpendicular to phi). The second-layer carbonate groups do not tilt, at least within measurement uncertainty. The spacing between Mn atom layers remains unchanged within measurement error whereas the spacing between layers of C atoms in carbonate contracts for the top three layers. Knowledge of the detailed atomic structure of the hydrated (1014) surface of MnCO3 provides a structural baseline for the interpretation of chemical reactivity.
authors.affiliation: School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Young-Shin
authors.initials: YS
authors.lastname: Jun
authors.forename: Sanjit K
authors.initials: SK
authors.lastname: Ghose
authors.forename: Thomas P
authors.initials: TP
authors.lastname: Trainor
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Eng
authors.forename: Scot T
authors.initials: ST
authors.lastname: Martin
mesh_terms: D002254:Carbonates / Q000737:chemistry*; D006813:Humidity; D008345:Manganese / Q000737:chemistry*; D015394:Molecular Structure; D010100:Oxygen / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry
chemical_list: D002254:Carbonates; D014867:Water; D008345:Manganese; C045327:manganese carbonate; D010100:Oxygen