CO2 and CO monolayers on MgO(100) : LEED experiments and potential energy calculations

Abstract

The structure of CO 2 and CO monolayers adsorbed on MgO(100) single crystal surfaces has been determined by both LEED and semi-empirical potential calculations. The CO 2 overlayer forms a commensurate (2√2×2√2)R45 o solid phase at T≤93±1 K. The CO monolayer forms a (4×2) commensurate phase at T≤40 K which is transformed into a (3×2) phase when 41 K≤T≤49 K. Above 50 K, the CO monolayer expands uniaxially toward a (n×2) phase with a progressive loss of long-range order when temperature increases. Potential calculations interpret very well the stable geometry for CO 2 and the sequential stability of the various commensurate phases for CO