A theoretical study of adsorbate-adsorbate interactions on Ru(0001)

A theoretical study of adsorbate-adsorbate interactions on Ru(0001)
===================================================================

by J. J. Mortensen, B. Hammer, and J. K. Nørskov.

Surface Science, **414**, 315 (1998).

Abstract
--------

Using density functional theory we study the effect of pre-adsorbed
atoms on the dissociation of N2 and the adsorption of N, N2, and CO on
Ru(0001). We have done calculations for pre-adsorbed Na, Cs, and S, and
find that alkali atoms adsorbed close to a dissociating N2 molecule will
lower the barrier for dissociation, whereas S will increase it. The
interaction with alkali atoms is mainly of an electrostatic nature. The
poisoning by S is due to two kinds of repulsive interactions: a Pauli
repulsion and a reduced covalent bond strength between the adsorbate and
the surface d-ele ctrons. In order to investigate these different
interactions in more detail, we look at three different species (N
atoms, and terminally bonded N2 and CO) and use them as probes to study
their interaction with two modifier atoms (Na and S). The two modifier
atoms have very different properties, which allows us to decouple the
different types of interactions. Adsorbed Na induces large electrostatic
fields, which S does not, and S interacts strongly with Ru(4d) states
and broadens and shifts the d band, which Na does not do.