Potential energy hypersurfaces for the interaction of NO with the Ag(111) surface

Abstract

We present a new potential energy surface for the interaction of the NO molecule with a close-packed Ag(111) surface obtained using the recently developed corrected effective medium (CEM) method. The dual NO–Ag(111) interaction potentials, which reflect the electronic orbital degeneracy of the NO molecule in its ground(X 2Π) electronic state, were determined at a large variety of distances and orientations of the NO molecule above the surface, and for approach of the molecule over three different sites on the surface unit cell, described by a cluster of greater than 10 Ag atoms. The more than 600 calculated interaction energies were then fit to a compact analytic form, which allows the determination of the interaction potential at any position above the surface. The strongest binding corresponds to a nearly flat orientation of the NO molecule, with approach of the N end slightly preferred, and with the single antibonding π orbital of NO pointing toward the surface. In this geometry, the binding energy above, respectively, the atop, two-fold bridge, and three-fold center sites site is 2200, 1773, and 1574 cm−1. By contrast when the antibonding π electron is oriented in a plane parallel to the surface, the binding energy diminishes dramatically, and the dependence of the interaction energy on the orientation of the NO molecule is also diminished. Here, the three-fold center site is preferred, but with a well depth of only 885 cm−1 (0.110 eV).