Spatial distributions of desorbing products in steady-state NO and N2O reductions on Pd(110).
The angular and velocity distributions of desorbing product N(2) were examined over the crystal azimuth in steady-state NO+CO and N(2)O+CO reactions on Pd(110) by cross-correlation time-of-flight techniques. At surface temperatures below 600 K, N(2) desorption in both reactions splits into two directional lobes collimated along 41 degrees -45 degrees from the surface normal toward the [001] and [001] directions. Above 600 K, the normally directed N(2) desorption is enhanced in the NO reduction. Each product desorption component, as well as CO(2), shows a fairly asymmetric distribution about its collimation axis. Two factors, i.e., the anisotropic site structures and the reactant orientation and movements, are operative to induce such asymmetry, depending on the product emission mechanism.
Kinetics of the N2O-CO reaction on Rh(110)
Abstract Our recent studies of the steady-state kinetics of the N 2 O–CO reaction on Rh(1 1 0) indicate that at CO excess, the reaction rate increases with increasing temperature. At N 2 O excess, the reaction rate is nearly independent of temperature at T T  > 520 K. Our present analysis of the relevant data indicates that the latter feature seems to be related to surface-oxide formation. Following this line, we propose a mean-field kinetic model making it possible to describe and clarify the experiment.
Effective symmetry of a lattice of molecules adsorbed on a substrate lattice
Abstract A procedure for determining the group describing the symmetry of the system adsorbate-plus-substrate, is presented for systems in which both the adsorbate and substrate have two-dimensional lattices. Site group operations for the combined adsorbate-plus-substrate lattice are shown to be those operations which may be simultaneously applied to both adsorbate and substrate lattices. In the low barrier to rotation limit for adsorbed molecules, a new combined lattice is required to describe the system adsorbate-plus-substrate. The symmetry operations of the factor group appropriate for adsorbed molecules experiencing low barriers to rotation can be derived from the point group of the free molecule, the site group in the high barrier to rotation limit, and the factor group of the combined lattice in the high barrier to rotation limit. Examples are given to illustrate the procedures.