Bound Nuclear Spin States of H-2 in an Anisotropic Potential Induced by a Stepped Metal Surface

The authors report an investigation of the nuclear spin bound states of H2 molecularly chemisorbed on a Pd(210) surface. They found that the adiabatic potential energy surface obtained from total energy density functional theory-based calculations is strongly anisotropic originating from the symmetry of surface-molecule bonding. Such a potential anisotropy causes a significant splitting of the J, states resulting in a relatively larger desorption energy difference between ortho and para isomers than on flat metal surfaces. Rotational–vibrational calculations show that two lowest bound state levels belong to para and ortho species, respectively. The corresponding wave functions show a highly localized adsorption character on top of the step-edge Pd and molecular orientation θ = π/2.