Invited Paper SS1-WeA2
Nano-Structural Information Carried by Desorbing Products; Surface-Nitrogen Removal and Angular Distributions

Wednesday, October 17, 2007, 2:00 pm, Room 608

Angle-resolved (AR) product desorption analysis assigns active surface species directly emitting products. Its application is limited to products with hyper-thermal energy. This paper delivers the analysis of surface-nitrogen removal processes in both the thermal decomposition of adsorbed N2O and steady-state NO reduction on Rh(100), Rh(110) and Pd(110), in which desorbing nitrogen holds high kinetic energy. In the thermal decomposition of N2O(a) on Rh(100), N2 desorption shows two peaks at around 85 K and 110 K. At low N2O coverage, the desorption at 85 K collimates at about 66 degrees off normal toward the [001] direction, whereas at high coverage, it sharply collimates along the surface normal. In the steady-state NO+D2 reaction on Rh(100), the N2 desorption preferentially collimates at around 71 degrees off normal toward the [001] direction at 550-700 K, whereas it collimates predominantly along the surface normal at higher temperatures. At lower temperatures, the surface nitrogen removal in the NO reduction is due to NO(a)+N(a) to N2O(a) to N2(g)+O(a), whereas, at higher temperatures, the associative desorption of nitrogen adatoms is predominant. This NO reduction mechanism is also operative on Rh(110) and Pd(110) with different contributions from the two pathways. The emission angle of nascent N2 is controlled by the orientation of adsorbed N2O and the collimation angle of desorbing N2 is also affected by co-adsorbed species. In the steady-state N2O+D2 reaction on Rh(110), the N2 desorption collimates closely along the [001] direction (close to the surface parallel) below 340 K and shifts to ca. 65 degrees off normal at higher temperatures. In the reduction with CO, the N2 desorption collimates along around 65 degrees off normal toward the [001] direction above 520 K, and shifts to 45 degrees at 445 K with decreasing surface temperature. In this temperature range, adsorbed CO increases and scatters the product N2.