DYNAMICS OF COMMENSURATE (NX2, N = 3, 4) AND INCOMMENSURATE PHASES OF AN ARGON MONOLAYER ADSORBED ON MGO(100)

Calculations of the dynamics of three different geometries of an Ar monolayer adsorbed on the MgO(100) substrate are developed within the harmonic approximation in order to determine the dispersion relations, the vibrational spectrum and the inelastic neutron scattering cross section. Several energy loss peaks are obtained for the (3 x 2), (4 x 2) commensurate and hexagonal incommensurate geometries. Their shapes and energies strongly depend on the geometry of the adsorbed phase and they can be interpreted as the result of unequivalent adsorption sites for the monolayer atoms. The comparison with the first available inelastic scattering spectra for the (3 x 2) structure shows that it is possible, at high resolution, to exhibit the various peaks and to interpret them with the present calculations.