The potential energy surface for dissociation of N2 on W()

Molecular trapping in the dissociation dynamics of N2 on W(110)

“…This is consistent with the weakly bound c-nitrogen adsorption state [30], although we find that the adsorption energy increases to 0.4 eV if the substrate is allowed to relax (the W atom bonding to the molecule relaxes 0.13 A outwards, the other atoms in the top layer relax 0.06 A inwards). The binding energy in this configuration is considerably smaller than the $1.5 eV found for the equivalent geometry on the W(1 0 0) surface [20]. As we shall show below, the 0.24 eV well is still deep enough to induce steering of the incoming molecules.…”

“…If the molecule is constrained to lie parallel to the surface, the barrier to dissociation is never smaller than 1 eV, even for molecules oriented across a bridge site, which as we shall see below is a critical orientation in dissociation, in that all dissociation occurs there. The dissociation barrier for parallel oriented molecules is higher than the minimum direct activation barrier ($0.5 eV) on the more open and reactive (1 0 0) surface [20].…”

“…Several molecular precursor states have been identified by EELS [19], corresponding to different bonding configurations of the molecules on the surface. These have been confirmed by density functional calculation [20]. In contrast to this, the dissociation of N 2 on the W(1 1 0) surface is far less facile and is believed to occur by a direct activated mechanism, as indicated by a monotonically increasing dissociation probability [11] (the influence of surface temperature has not been studied).…”

“…The RPBE functional has been extensively used for nitrogen adsorption on metals [24,28,29], it corrects for some overbinding produced by the PW91 functional [27], however it may result in an overestimation of dissociation barriers. Computations were performed with either 9 or 13 k-points in the symmetry reduced set, and a cutoff energy of 300 eV, as in previous work [20]. Molecules were adsorbed in a 2 · 2 unit cell on a 5 layer slab with structure optimized by allowing the outer two W layers to relax (the relaxed structure is essentially identical to the bulk truncation).…”

“…As on the W(1 0 0) surface [20], we can see from the curve labelled ''atop-vertical'', that a molecule…”