title: Structure of interfacial water on fluorapatite (100) surface.
abstract: The structure relaxation mechanism of the fluorapatite (100) surface under completely hydrated ambient conditions has been investigated with the grazing incidence X-ray diffraction (GIXRD) technique. Detailed information on lateral as well as perpendicular ordering corresponding to the water molecules and atomic relaxations of the (100) surface of fluorapatite (FAp) crystal was obtained from the experimental analysis of the CTR intensities. Two laterally ordered water layers are present at the water/mineral interface. The first layer consists of four water molecules located at 1.6(1) A above the relaxed fluorapatite (100) surface while the second shows the presence of only two water molecules at a distance of 3.18(10) A from the mineral surface. Thus, the first layer water molecules complete the truncated coordination sites of the topmost surface Ca atoms, while the second water layer molecules remain bonded by means of H-bonding to the first layer molecules and the surface phosphate groups. Molecular mechanics simulations using force field techniques are in good agreement with this general structural behavior determined from the experiment.
authors.affiliation: Faculty of Geosciences, Department of Geology, Mineralogy and Geophysics, Ruhr-Universitaet Bochum, Universitaetsstrasse 150, 44780 Bochum, Germany. aparna.pareek@ruhr-uni-bochum.de
authors.forename: Aparna
authors.initials: A
authors.lastname: Pareek
authors.forename: Xavier
authors.initials: X
authors.lastname: Torrelles
authors.forename: Klaus
authors.initials: K
authors.lastname: Angermund
authors.forename: Jordi
authors.initials: J
authors.lastname: Rius
authors.forename: Uta
authors.initials: U
authors.lastname: Magdans
authors.forename: Hermann
authors.initials: H
authors.lastname: Gies
mesh_terms: D001031:Apatites / Q000737:chemistry*; D003198:Computer Simulation; D013499:Surface Properties; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D001031:Apatites; D014867:Water; C025105:fluorapatite