WATER MOLECULE POSITIONS, ORIENTATIONS, AND MOTIONS IN THE DIHYDRATES OF MG AND NA VERMICULITES

Using a simple ionic bonding model, the stable hydrogen positions for the water molecules have been determined for two-layer hydrates of vermiculite saturated with Na or Mg. The energies required to rotate the water molecules about (1) a vertical OH, (2) the C2 axis, as well as (3) the whole hydration shell about the vertical C3 axis have been calculated. A combination of motions involving the C3 and C2 is likely while the rotation about an OH is unlikely. Because of the different environments about the hydrated cations (Mg or Na), the type of motion which is most probable (requires the least energy) is very different. © 1979.