Diffraction of molecular hydrogen from metal surfaces

► Diffraction of H2 is a sensitive tool to characterize the 6D PES for H2 dissociation at metal surfaces. ► Elastic and rotationally inelastic direction peaks are observed at incident energies between 20 and 200 meV. ► H2 diffraction samples the PES in a region around 2 Å away from the surface atom nuclei. ► Experimental and theoretical state-of-the-art studies at metal surfaces are reviewed.