Molecular-scale density oscillations in water adjacent to a mica surface -art. no. 156103

High-resolution specular x-ray reflectivity of the mica(001)-water interfac e under ambient conditions reveals oscillations in water oxygen density in the surface-normal direction, giving evidence of interfacial water ordering . The spacings between neighboring water layers in the near-surface, strong ly oscillatory region are 2.5(2)-2.7(2) Angstrom, approximately the size of the water molecule. The density oscillations extend to about 10 Angstrom a bove the surface and do not strictly maintain a solvent-size periodicity as that in interfacial liquid metal and hard-sphere molecular liquids. We int erpret this oscillatory density profile of the interfacial water as due to the "hard-wall" effect of the molecularly smooth mica surface.