ISOTOPIC ORDERING IN ADSORBED HYDROGEN SINGLE LAYERS

The isotopic ordering of H-2-D-2 mixtures adsorbed at low temperature on graphite in the monolayer range is measured by small angle neutron scattering (SANS). We show that below 8 K, solid mixtures exhibit isot opic clustering at large density (monolayer completion) and a tendency towards the formation of ordered compounds for smaller density (near the commensurate structure).