Observation of the second ordered phase of water on the MgO(100) surface: Low energy electron diffraction and helium atom scattering studies

The interaction of water with MgO (100) single crystal surfaces cleaved in situ has been studied by low energy electron diffraction and helium atom scattering in the temperature range 80 K-230 K. At T-crystal=100-180 K water forms a layer with a c(4X2) symmetry in good agreement with previous spot profile analysis of low energy electron diffraction experiments. Adsorption at T-crystal=185-221 K leads to the formation of a new ordered phase. The results of the low energy electron diffraction and elastic helium atom scattering experiments show that this high-temperature phase has a (3X2) symmetry, and that the unit cell contains a glide plane. The isosteric heat of adsorption at half coverage Q(st)=85.3 kJ/mol has been determined from equilibrium adsorption isotherms measured between 210 and 221 K. (C) 1996 American Institute of Physics.