CRYSTAL-FACE DEPENDENCE OF PHYSISORPTION POTENTIALS

We have measured a crystal face dependence of the physisorption energies for H-2 and D2 interacting with the Cu(111), Cu(100), and Cu(110) surfaces. The trend of potential-well depths, D111 < D100 < D110, is the opposite of that predicted by existing theory. We argue that a larger binding energy for an open crystal face is a consequence of the face-dependent electron-density profiles and their dynamical response, in particular, the influence on the attractive van der Waals interaction.