QUANTUM CHEMICAL STUDY OF CHEMISORPTION OF NITRIC OXIDE ON ALUMINUM (111) SURFACE

Abstract

The interaction of Nitric Oxide (NO) with Al (111) surfaces including clusters has been studied
by means of semi-empirical AM1 method. Metal cluster models (up to 51 atoms) with different
sizes and geometries have been used to describe the atop, bridge and three-fold sites. The
binding energies of NO in different geometries are calculated and compared with the results
from the experimental data available and the previous study. GAMESS and OpenMX quantum
chemical programs were used to compute the binding energies of the system and the
geometrical properties of the initial and optimized clusters obtained from MOLDEN and
RasMol packages respectively. The NO tilted upright with respect to the surface normal axis
when adsorbed on top, bridge and three-fold sites and nitrogen atom is pointing towards the
surface. The cluster model approach is discussed in terms of its reliability to determine the
adsorption energies and the favored site of adsorption. Based on the results, the more negative
value of binding energy obtained for small clusters (Al19 and Al21) in all on top, bridge and
three- fold site adsorptions. The most negative value of binding energy was obtained for
binding in bridge form in some cases and three-fold sites adsorption in all the other clusters.
Therefore it is concluded that the NO adsorbs preferentially on bridge and also three-fold sites
in all the cluster models. Since the geometry optimization of on top converged to bridge, close
to bridge and the three-fold site geometry after geometry optimization, it can be concluded that
on top adsorptions are comparatively unstable.