Neutron diffraction investigation of water on MgO(001) surfaces, from monolayer to bulk condensation

The structure of D2O molecules adsorbed on MgO(001) surfaces has been studi ed by neutron diffraction within the 200-273 K temperature range and at cov erages (theta) of 0.93, 1.5, 4 and 20 monolayers (ML). At low coverage (the ta less than or equal to 1.5 ML) and whatever the temperature, the two-dime nsional (2D) analysis of the monolayer structure is compatible with the pre viously observed p(3 x 2) commensurate phase, but presenting a short cohere nce length of 35 +/- 5 Angstrom. At higher coverages, we show that this 2D ordered phase coexists with the bulk phase. These results confirm the outst anding stability of the water monolayer adsorbed on MgO(001) found by recen t molecular dynamics calculations. (C) 2000 Elsevier Science B.V. All right s reserved.