NO Adsorption and Thermal Behavior on Pd(112): The Effect of Surface Modification by O and Ge

The effect of O(a) and Ge(a) on the adsorption of NO on the stepped Pd(112) surface has been studied by temperature programmed desorption (TPD), Auger electron spectroscopy (AES), secondary electron emission crystal current (SEECC), low energy electron diffraction (LEED), and electron stimulated desorption ion angular distribution (ESDIAD) methods. The presence of either O or Ge at the Pd(112) surface alters the kinetics of NO thermal desorption, destablizing the NO which subsequently desorbs at lower temperatures. The dissociative NO channels, which produce N[sub 2] and N[sub 2]O as products, are simultaneously suppressed by the preadsorption of O or Ge. The similarities between the NO/O/Pd(112) and NO/Ge/Pd(112) results lead to the conclusion that steric blocking is more important than electronic poisoning effects in these systems. O[sup +] ESDIAD patterns from NO/Pd(112) are essentially identical to those from NO/O/Pd(112) and NO/Ge/Pd(112), implying that the surface modifiers do not preferentially block the step sites toward NO adsorption. The ESDIAD data are interpreted in terms of the random adsorption of O and Ge on the surface. 24 refs., 12 figs.