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The angular and velocity distributions of desorbing products N2 and CO2 were studied in a steady-state NO + CO reaction on Pd(110) and Rh(110) by cross-correlation time-of-flight techniques. The CO2 desorption sharply collimated along the surface normal on both surfaces. On the other hand, N2 desorption on Pd(110) sharply collimated along about 40° off the surface normal in the plane along the [001] direction below around 650 K, yielding a translational temperature of about 3600 K. At higher temperatures, the normally directed desorption was relatively enhanced. On Rh(110), desorbing N2 sharply collimated along the surface normal, yielding a translational temperature of about 2500 K. The inclined desorption was assigned to the decomposition of the intermediate, N2O(a) → N2(g) + O(a), and the normally directed component was proposed to be due to the associative desorption of adsorbed nitrogen atoms, 2N(a) → N2(g). The branching of these pathways was analyzed on Pd(110).

The adsorption of nitrous oxide N 2 O on the Pd(110) surface has been studied and characterized using densityfunctional theory. We found that N 2 O binds weakly to the surface in two alternative forms, either tilted with the terminal N atom attached to the surface or lying horizontally on the surface in the [001] direction. The adsorption on the on-top site is more stable than that on the bridge one. The horizontal form of N 2 O(a) is appropriate as the precursor of the inclined desorption of the product N 2 observed in the thermal decomposition of N 2 O(a).

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O and NO showed a cosine angular distribution and a Maxwellian velocity distribution at the surface temperature. On the other hand, the N 2 desorption collimated sharply at Ϯ41°-43°off the surface normal in a plane along the ͓001͔ direction. Then the velocity distributions of N 2 involved two hyperthermal components with the mean translational energy of 0.47 and 0.22 eV, respectively. A mechanism for the inclined N 2 desorption was proposed to be due to a highly exothermic reaction of N 2 O͑ad͒→N 2 (g)ϩO͑ad͒ and the strong repulsive force operative on the product N 2 from the surface.

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